Webb peers into the Extreme Outer Galaxy and the Digel Clouds
Within the Milky Way’s outskirts is a firecracker show of star formation. The NASA/ESA/CSA James Webb Space Telescope has examined the fringes of our Milky Way galaxy and Webb’s near- and mid-infrared imaging capabilities have enabled scientists to examine a star-forming area reminiscent of our galaxy during its early stages of formation.
The NASA/ESA/CSA James Webb Space Telescope has observed the very outskirts of our Milky Way galaxy. Known as the Extreme Outer Galaxy, this region is located more than 58 000 light-years from the Galactic centre. To learn more about how a local environment affects the star formation process within it, a team of scientists directed the telescope’s NIRCam (Near-InfraRed Camera) and MIRI (Mid-InfraRed Instrument) towards a total of four star-forming areas within Digel Clouds 1 and 2: 1A, 1B, 2N, and 2S. In the case of Cloud 2S, shown here, Webb revealed a luminous main cluster that contains newly formed stars. Several of these young stars are emitting extended jets of material from their poles. To the main cluster’s top right is a sub-cluster of stars, a feature that scientists previously suspected to exist but has now been confirmed with Webb. Additionally, the telescope revealed a deep sea of background galaxies and red nebulous structures that are being carved away by winds and radiation from nearby stars. Credit: NASA, ESA, CSA, STScI, M. Ressler (NASA-JPL)
Astronomers have directed the NASA/ESA/CSA James Webb Space Telescope to examine the outskirts of our Milky Way galaxy, a region scientists call the Extreme Outer Galaxy owing to its location more than 58 000 light-years away from the Galactic centre. For comparison, Earth is approximately 26 000 light-years from the centre.
A team of scientists used Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) to image selected regions within two molecular clouds known as Digel Clouds 1 and 2. Thanks to its high sensitivity and sharp resolution, Webb was able to resolve these areas, which are hosts to star clusters undergoing bursts of star formation, in unprecedented detail. Some of the details revealed by these data include components of the clusters such as very young (Class 0) protostars, outflows and jets, and distinctive nebular structures.
These Webb observations are enabling scientists to study star formation in the outer Milky Way at the same level of detail as observations of star formation in our own solar neighbourhood.
Stars in the making
Although the Digel Clouds are within our galaxy, they are relatively poor in elements heavier than hydrogen and helium. This composition makes them similar to dwarf galaxies and our own Milky Way in its early history. The team therefore took the opportunity to use Webb to capture the activity in four clusters of young stars within Digel Clouds 1 and 2: 1A, 1B, 2N, and 2S.
In Cloud 2S, Webb captured the main cluster containing young, newly formed stars. This dense area is quite active and several stars are emitting extended jets of material along their poles. Additionally, while scientists previously suspected a sub-cluster might be present within the cloud, Webb’s imaging capabilities confirmed its existence for the first time. Webb’s data reveal that there are multiple jets shooting out in different directions from this cluster of stars.
The saga of stars
This Webb imagery of the Extreme Outer Galaxy and the Digel Clouds is just a starting point for the team. They intend to revisit this Milky Way outpost to find answers to a variety of current questions, including the relative abundance of stars of various masses within Extreme Outer Galaxy star clusters, a measurement that would help astronomers understand how a particular environment can influence different types of stars during their formation.
Though the story of star formation is complex and some chapters are still shrouded in mystery, Webb is gathering clues and helping astronomers unravel this intricate tale.
The observations were taken as part of Guaranteed Time Observation program 1237.
Annotated image of Digel Cloud 2S captured by Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument), with compass arrows, a scale bar, colour key, and graphic overlays for reference. The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above). The scale bar is labelled in light-years and arcseconds. One light-year is equal to about 9.46 trillion kilometres. One arcsecond is equal to 1/3600 of one degree of arc (the full Moon has an angular diameter of about 0.5 degrees). The actual size of an object that covers one arcsecond on the sky depends on its distance from the telescope. This image shows invisible near- and mid-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which NIRCam and MIRI filters were used when collecting the light. The colour of each filter name is the visible light colour used to represent the infrared light that passes through that filter. In the main cluster are five white arrows, which highlight the paths of five protostar jets. Credit: NASA, ESA, CSA, STScI, M. Ressler (NASA-JPL)
Webb images of Epsilon Indi Ab, a cold exoplanet 12 light-years away
An international team of astronomers using the NASA/ESA/CSA James Webb Space Telescope have directly imaged an exoplanet roughly 12 light-years from Earth. While there were hints that the planet existed, it had not been confirmed until Webb imaged it. The planet is one of the coldest exoplanets observed to date.
The planet, known Epsilon Indi Ab, is several times the mass of Jupiter and orbits the K-type star Epsilon Indi A (Eps Ind A), which is around the age of our Sun, but slightly cooler. The team observed Epsilon Indi Ab using the coronagraph on Webb’s MIRI (Mid-Infrared Instrument). Only a few tens of exoplanets have been directly imaged previously by space- and ground-based observatories.
“Our prior observations of this system have been more indirect measurements of the star, which actually allowed us to see ahead of time that there was likely a giant planet in this system tugging on the star,” said team member Caroline Morley of the University of Texas at Austin. “That’s why our team chose this system to observe first with Webb.”
“This discovery is exciting because the planet is quite similar to Jupiter — it is a little warmer and is more massive, but is more similar to Jupiter than any other planet that has been imaged so far,” added lead author Elisabeth Matthews of the Max Planck Institute for Astronomy in Germany.
A Solar System analog
Previously imaged exoplanets tend to be the youngest, hottest exoplanets that are still radiating much of the energy from when they first formed. As planets cool and contract over their lifetime, they become significantly fainter and therefore harder to image.
“Cold planets are very faint, and most of their emission is in the mid-infrared,” explained Matthews. “Webb is ideally suited to conduct mid-infrared imaging, which is extremely hard to do from the ground. We also needed good spatial resolution to separate the planet and the star in our images, and the large Webb mirror is extremely helpful in this aspect.”
Epsilon Indi Ab is one of the coldest exoplanets to be directly detected, with an estimated temperature of 2 degrees Celsius — colder than any other imaged planet beyond our Solar System, and colder than all but one free-floating brown dwarf [1]. The planet is only around 100 degrees Celsius warmer than gas giants in our Solar System. This provides a rare opportunity for astronomers to study the atmospheric composition of true solar system analogs.
“Astronomers have been imagining planets in this system for decades; fictional planets orbiting Epsilon Indi have been the sites of Star Trek episodes, novels, and video games like Halo,” added Morley. “It’s exciting to actually see a planet there ourselves, and begin to measure its properties.”
Not quite as predicted
Epsilon Indi Ab is the twelfth closest exoplanet to Earth known to date and the closest planet more massive than Jupiter. The science team chose to study Eps Ind A because the system showed hints of a possible planetary body using a technique called radial velocity, which measures the back-and-forth wobbles of the host star along our line of sight.
“While we expected to image a planet in this system, because there were radial velocity indications of its presence, the planet we found isn’t what we had predicted,” shared Matthews. “It’s about twice as massive, a little farther from its star, and has a different orbit than we expected. The cause of this discrepancy remains an open question. The atmosphere of the planet also appears to be a little different than the model predictions. So far we only have a few photometric measurements of the atmosphere, meaning that it is hard to draw conclusions, but the planet is fainter than expected at shorter wavelengths.”
The team believes this may mean there is significant methane, carbon monoxide, and carbon dioxide in the planet’s atmosphere that are absorbing the shorter wavelengths of light. It might also suggest a very cloudy atmosphere.
The direct imaging of exoplanets is particularly valuable for characterization. Scientists can directly collect light from the observed planet and compare its brightness at different wavelengths. So far, the science team has only detected Epsilon Indi Ab at a few wavelengths, but they hope to revisit the planet with Webb to conduct both photometric and spectroscopic observations in the future. They also hope to detect other similar planets with Webb to find possible trends about their atmospheres and how these objects form.
These results were taken with Webb’s Cycle 1 GO programme #2243 and have been published today in Nature.
This image of the gas-giant exoplanet Epsilon Indi Ab was taken with the coronagraph on the NASA/ESA/CSA James Webb Space Telescope’s MIRI (Mid-Infrared Instrument). A star symbol marks the location of the host star Epsilon Indi A, whose light has been blocked by the coronagraph, resulting in the dark circle marked with a dashed white line. Epsilon Indi Ab is one of the coldest exoplanets ever directly imaged. Light at 10.6 microns was assigned the color blue, while light at 15.5 microns was assigned the color orange. MIRI did not resolve the planet, which is a point source. Credit: ESA/Webb, NASA, CSA, STScI, E. Matthews (Max Planck Institute for Astronomy)
Vivid portrait of interacting galaxies, Penguin and Egg, marks Webb’s second anniversary
The distorted spiral galaxy, the Penguin, and the compact elliptical galaxy, the Egg, are locked in an active embrace. A new near- and mid-infrared image from the James Webb Space Telescope, taken to mark its second year of science, shows that their interaction is marked by a faint upside-down U-shaped blue glow. The pair, known jointly as Arp 142, made their first pass between 25 and 75 million years ago — causing ‘fireworks’, or new star formation, in the Penguin. In the most extreme cases, mergers can cause galaxies to form thousands of new stars per year for a few million years. For the Penguin, research has shown that about 100 to 200 stars have formed per year. By comparison, our Milky Way galaxy (which is not interacting with a galaxy of the same size) forms roughly six to seven new stars per year. This gravitational shimmy also remade the Penguin’s appearance. Its coiled spiral arms unwound, and gas and dust were pulled in an array of directions, like it was releasing confetti. It is rare for individual stars to collide when galaxies interact (space is vast), but the galaxies’ mingling disrupts their stars’ orbits. Today, the Penguin’s galactic centre looks like an eye set within a head, and the galaxy has prominent star trails that take the shape of a beak, backbone, and fanned-out tail. A faint, but prominent dust lane extends from its beak down to its tail. Despite the Penguin appearing far larger than the Egg, these galaxies have approximately the same mass. This is one reason why the smaller-looking Egg hasn’t yet merged with the Penguin. (If one was less massive, it may have merged earlier.) The oval Egg is filled with old stars, and little gas and dust, which is why it isn’t sending out ‘streamers’ or tidal tails of its own and instead has maintained a compact oval shape. If you look closely, the Egg has four prominent diffraction spikes — the galaxy’s stars are so concentrated that it gleams. The background of this image is overflowing with far more distant galaxies. This is a testament to the sensitivity and resolution of Webb’s infrared cameras. Arp 142 lies 326 million light-years from Earth in the constellation Hydra. Credit: NASA, ESA, CSA, STScI
A duo of interacting galaxies known as Arp 142 commemorates the second science anniversary of the NASA/ESA/CSA James Webb Space Telescope. Their ongoing interaction was set in motion between 25 and 75 million years ago, when the Penguin (individually catalogued as NGC 2936) and the Egg (NGC 2937) completed their first pass. They will go on to shimmy and sway, completing several additional loops before merging into a single galaxy hundreds of millions of years from now.
The James Webb Space Telescope takes constant observations, including images and highly detailed data known as spectra. Its operations have led to a ‘parade’ of discoveries by astronomers around the world. It has never felt more possible to explore every facet of the Universe.
The telescope’s specialisation in capturing infrared light – which is beyond what our own eyes can detect – shows these galaxies, collectively known as Arp 142, locked in a slow cosmic dance. Webb’s observations (which combine near- and mid-infrared light from Webb’s NIRCam [Near-InfraRed Camera] and MIRI [Mid-Infrared Instrument], respectively) clearly show that they are joined by a blue haze that is a mix of stars and gas, a result of their mingling.
The distorted spiral galaxy at the centre, the Penguin, and the compact elliptical galaxy at the left, the Egg, are locked in an active embrace. A new near- and mid-infrared image from the James Webb Space Telescope, taken to mark its second year of science, shows that their interaction is marked by a faint upside-down U-shaped blue glow. The pair, known jointly as Arp 142, made their first pass between 25 and 75 million years ago — causing ‘fireworks’, or new star formation, in the Penguin. In the most extreme cases, mergers can cause galaxies to form thousands of new stars per year for a few million years. For the Penguin, research has shown that about 100 to 200 stars have formed per year. By comparison, our Milky Way galaxy (which is not interacting with a galaxy of the same size) forms roughly six to seven new stars per year. This gravitational shimmy also remade the Penguin’s appearance. Its coiled spiral arms unwound, and gas and dust were pulled in an array of directions, like it was releasing confetti. It is rare for individual stars to collide when galaxies interact (space is vast), but the galaxies’ mingling disrupts their stars’ orbits. Today, the Penguin’s galactic centre looks like an eye set within a head, and the galaxy has prominent star trails that take the shape of a beak, backbone, and fanned-out tail. A faint, but prominent dust lane extends from its beak down to its tail. Despite the Penguin appearing far larger than the Egg, these galaxies have approximately the same mass. This is one reason why the smaller-looking Egg hasn’t yet merged with the Penguin. (If one was less massive, it may have merged earlier.) The oval Egg is filled with old stars, and little gas and dust, which is why it isn’t sending out ‘streamers’ or tidal tails of its own and instead has maintained a compact oval shape. If you look closely, the Egg has four prominent diffraction spikes — the galaxy’s stars are so concentrated that it gleams. Now, find the bright, edge-on galaxy at top right. It may look like a party crasher, but it’s not nearby. Cataloged PGC 1237172, it lies 100 million light-years closer to Earth. It is relatively young and isn’t overflowing with dust, which is why it practically disappears in Webb’s mid-infrared view. The background of this image is overflowing with far more distant galaxies. This is a testament to the sensitivity and resolution of Webb’s infrared cameras. Arp 142 lies 326 million light-years from Earth in the constellation Hydra. Credit: NASA, ESA, CSA, STScI
Let’s dance
Before their first approach, the Penguin held the shape of a spiral. Today, its galactic centre gleams like an eye, its unwound arms now shaping a beak, head, backbone, and fanned-out tail.
Like all spiral galaxies, the Penguin is still very rich in gas and dust. The galaxies’ ‘dance’ pulled gravitationally on the Penguin’s thinner areas of gas and dust, causing them to crash in waves and form stars. Look for those areas in two places: what looks like a fish in its ‘beak’ and the ‘feathers’ in its “‘tail’.
Surrounding these newer stars is smoke-like material that includes carbon-containing molecules, known as polycyclic aromatic hydrocarbons, which Webb is exceptional at detecting. Dust, seen as fainter, deeper orange arcs also swoops from its beak to tail feathers.
Webb’s mid-infrared view of interacting galaxies Arp 142 seems to sing in primary colours. The background of space is like a yawning darkness speckled with bright, multi-coloured beads. This image was taken by MIRI, the telescope’s Mid-InfraRed Instrument, which astronomers use to study cooler and older objects, dust, and extremely distant galaxies. Here, the Egg appears as an exceptionally small teal oval with gauzy layers. Mid-infrared light predominantly shows the oldest stars in the elliptical galaxy, which has lost or used up most of its gas and dust. This is why the view is so different from the combined image, which includes near-infrared light. At right, the Penguin’s shape is relatively unchanged. The MIRI image shows all the gas and dust that has been distorted and stretched, as well as the smoke-like material, in blue, that includes carbon-containing molecules, known as polycyclic aromatic hydrocarbons. Next, look for the edge-on galaxy catalogued PGC 1237172 at the top right — a dim, hazy line. Find it by looking for the bright blue star with small diffraction spikes positioned over the top of its left edge. This galaxy nearly disappears in mid-infrared light because its stars are very young and the galaxy isn’t overflowing with dust. Now, scan the full image left to right to spot distant galaxies in the background. The red objects are encased in thick layers of dust. Some are spiral galaxies and others are more distant galaxies that can only be detected as dots or smudges. Green galaxies are laden with dust and are farther away. Bluer galaxies are closer. Zoom in carefully to see if a blue dot has minuscule diffraction spikes — those are stars, not galaxies. Credit: NASA, ESA, CSA, STScI
In contrast, the Egg’s compact shape remains largely unchanged. As an elliptical galaxy, it is filled with ageing stars, and has a lot less gas and dust that can be pulled away to form new stars. If both were spiral galaxies, each would end the first ‘twist’ with new star formation and twirling curls, known as tidal tails.
Another reason for the Egg’s undisturbed appearance is that these galaxies have approximately the same mass, which is why the smaller-looking elliptical wasn’t consumed or distorted by the Penguin.
It is estimated that the Penguin and the Egg are about 100 000 light-years apart — quite close in astronomical terms. For context, the Milky Way galaxy and our nearest neighbour, the Andromeda Galaxy, are about 2.5 million light-years apart, about 30 times the distance. They too will interact, but not for about 4 billion years.
The distorted spiral galaxy at the centre, the Penguin, and the compact elliptical galaxy at the left, the Egg, are locked in an active embrace. A new near- and mid-infrared image from the James Webb Space Telescope, taken to mark its second year of science, shows that their interaction is marked by a faint upside-down U-shaped blue glow. The pair, known jointly as Arp 142, made their first pass between 25 and 75 million years ago — causing ‘fireworks’, or new star formation, in the Penguin. In the most extreme cases, mergers can cause galaxies to form thousands of new stars per year for a few million years. For the Penguin, research has shown that about 100 to 200 stars have formed per year. By comparison, our Milky Way galaxy (which is not interacting with a galaxy of the same size) forms roughly six to seven new stars per year. This gravitational shimmy also remade the Penguin’s appearance. Its coiled spiral arms unwound, and gas and dust were pulled in an array of directions, like it was releasing confetti. It is rare for individual stars to collide when galaxies interact (space is vast), but the galaxies’ mingling disrupts their stars’ orbits. Today, the Penguin’s galactic centre looks like an eye set within a head, and the galaxy has prominent star trails that take the shape of a beak, backbone, and fanned-out tail. A faint, but prominent dust lane extends from its beak down to its tail. Despite the Penguin appearing far larger than the Egg, these galaxies have approximately the same mass. This is one reason why the smaller-looking Egg hasn’t yet merged with the Penguin. (If one was less massive, it may have merged earlier.) The oval Egg is filled with old stars, and little gas and dust, which is why it isn’t sending out ‘streamers’ or tidal tails of its own and instead has maintained a compact oval shape. If you look closely, the Egg has four prominent diffraction spikes — the galaxy’s stars are so concentrated that it gleams. Now, find the bright, edge-on galaxy at top right. It may look like a party crasher, but it’s not nearby. Cataloged PGC 1237172, it lies 100 million light-years closer to Earth. It is relatively young and isn’t overflowing with dust, which is why it practically disappears in Webb’s mid-infrared view. The background of this image is overflowing with far more distant galaxies. This is a testament to the sensitivity and resolution of Webb’s infrared cameras. Arp 142 lies 326 million light-years from Earth in the constellation Hydra. Credit: NASA, ESA, CSA, STScI
In the top right of the image is an edge-on galaxy, catalogued PGC 1237172, which resides 100 million light-years closer to Earth. It’s also quite young, teeming with new, blue stars. In Webb’s mid-infrared-only image, PGC 1237172 practically disappears. Mid-infrared light largely captures cooler, older stars and an incredible amount of dust. Since the galaxy’s stellar population is so young, it ‘vanishes’ in mid-infrared light.
This image shows two views of Arp 142 (nicknamed the Penguin and the Egg). The image on the left from the NASA/ESA Hubble Space Telescope shows the target in 2013. On the right is the NASA/ESA/CSA James Webb Space Telescope’s view of the same region in near-infrared light with the NIRCam instrument. Both images are made up of several filters. The process of applying colour to Webb’s images is remarkably similar to the approach used for Hubble: the shortest wavelengths are assigned blue and the longest wavelengths are assigned red. For Webb, image processors translate near-infrared light images, in order, to visible colours. Both telescopes take high-resolution images, so there are many features to explore. In Hubble’s visible light image, a dark brown dust lane begins across the Penguin’s ‘beak’ and extends through its body and along its back. In Webb’s near-infrared view, this dust lane is significantly fainter. Linger on Webb’s image. A faint upside-down U shape joins the pair of galaxies. This is a combination of stars, gas, and dust that continues to mix as the galaxies mingle. In Hubble’s view, notice there is a clearer gap between the Penguin’s ‘beak’ and the top of the Egg. Toward the bottom of the Penguin’s tail are several prominent spiral galaxies, though there are a few more in Webb’s image. The Egg itself looks similar in both images, but in Webb’s view, the galaxy shines so brightly that it causes diffraction spikes to slightly extend its gleam. The galaxy at top right appears about the same size, but many more pinpricks of stars appear in Webb’s view. Now compare the backgrounds. Hubble shows many distant galaxies in visible light, though areas in the corners that are completely black were outside the telescope’s field of view. Many more distant galaxies gleam in Webb’s infrared image. This is a testament to the sensitivity and resolution of Webb’s near-infrared camera, and the advantages of infrared light. Light from distant galaxies is stretched as it travels across the Universe, so a significant portion of their light can only be detected at longer wavelengths. Explore Webb’s near- and mid-infrared light image and its mid-infrared light-only image. Credit: NASA, ESA, CSA, STScI
Webb’s image is also overflowing with distant galaxies. Some have spiral and oval shapes, like those threaded throughout the Penguin’s ‘tail feathers’, while others scattered throughout are shapeless dots. This is a testament to the sensitivity and resolution of the telescope’s infrared instruments. (Compare Webb’s view to the 2013 image from the NASA/ESA Hubble Space Telescope here.) Even though these observations only took a few hours, Webb revealed far more distant, redder, and dustier galaxies than previous telescopes — one more reason to expect Webb to continue to expand our understanding of everything in the Universe.
Arp 142 lies 326 million light-years from Earth in the constellation Hydra.
This image of interacting galaxies Arp 142, captured by the James Webb Space Telescope’s NIRCam (Near-InfraRed Camera) and MIRI (Mid-InfraRed Instrument), shows compass arrows, a scale bar, and a colour key for reference. The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above). The scale bar is labelled in light-years, which is the distance that light travels in one Earth-year. (It takes three years for light to travel a distance equal to the length of the scale bar.) One light-year is equal to about 9.46 trillion kilometres. The scale bar is also labelled in arcseconds, which is a measure of angular distance on the sky. One arcsecond is equal to an angular measurement of 1/3600 of one degree. There are 60 arcminutes in a degree and 60 arcseconds in an arcminute. (The full Moon has an angular diameter of about 30 arcminutes.) The actual size of an object that covers one arcsecond on the sky depends on its distance from the telescope. This image shows invisible near- and mid-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which NIRCam and MIRI filters were used when collecting the light. The name of each filter is the visible light colour used to represent the infrared light that passes through that filter. Credit: NASA, ESA, CSA, STScI
Webb has continued to produce incredible images of the cosmos, from the detailed beauty of the Ring Nebula, to supernova remnant Cassiopeia A, to a team effort with the the NASA/ESA Hubble Space Telescope and ESA’s Euclid telescope looking at the iconic Horsehead Nebula. Webb imagery was also combined with visible light observations from Hubble to create one of the most comprehensive views of the Universe ever, an image of galaxy cluster MACS 0416.
This image of interacting galaxies Arp 142, captured by the James Webb Space Telescope’s MIRI (Mid-Infrared Instrument), shows compass arrows, scale bar, and colour key for reference. The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above). The scale bar is labelled in light-years, which is the distance that light travels in one Earth-year. (It takes three years for light to travel a distance equal to the length of the scale bar.) One light-year is equal to about 9.46 trillion kilometres. The scale bar is also labelled in arcminutes, which is a measure of angular distance on the sky. One arcsecond is equal to an angular measurement of 1/3600 of one degree. There are 60 arcminutes in a degree and 60 arcseconds in an arcminute. (The full Moon has an angular diameter of about 30 arcminutes.) The actual size of an object that covers one arcsecond on the sky depends on its distance from the telescope. This image shows invisible near- and mid-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which NIRCam and MIRI filters were used when collecting the light. The name of each filter is the visible light colour used to represent the infrared light that passes through that filter. Credit: NASA, ESA, CSA, STScI
Hubble finds strong evidence for intermediate-mass black hole in Omega Centauri
An international team of astronomers has used more than 500 images from the NASA/ESA Hubble Space Telescope spanning two decades to detect seven fast-moving stars in the innermost region of Omega Centauri, the largest and brightest globular cluster in the sky. These stars provide compelling new evidence for the presence of an intermediate-mass black hole.
Intermediate-mass black holes (IMBHs) are a long-sought ‘missing link’ in black hole evolution. Only a few other IMBH candidates have been found to date. Most known black holes are either extremely massive, like the supermassive black holes that lie at the cores of large galaxies, or relatively lightweight, with a mass less than 100 times that of the Sun. Black holes are one of the most extreme environments humans are aware of, and so they are a testing ground for the laws of physics and our understanding of how the Universe works. If IMBHs exist, how common are they? Does a supermassive black hole grow from an IMBH? How do IMBHs themselves form? Are dense star clusters their favoured home?
Omega Centauri is visible from Earth with the naked eye and is one of the favourite celestial objects for stargazers in the southern hemisphere. Although the cluster is 17 700 light-years away, lying just above the plane of the Milky Way, it appears almost as large as the full Moon when seen from a dark rural area. The exact classification of Omega Centauri has evolved through time, as our ability to study it has improved. It was first listed in Ptolemy’s catalogue nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677, and in the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster.
Globular clusters typically consist of up to one million old stars tightly bound together by gravity and are found both in the outskirts and central regions of many galaxies, including our own. Omega Centauri has several characteristics that distinguish it from other globular clusters: it rotates faster than a run-of-the-mill globular cluster, and its shape is highly flattened. Moreover, Omega Centauri is about 10 times as massive as other big globular clusters, almost as massive as a small galaxy.
An international team of astronomers has used more than 500 images from the NASA/ESA Hubble Space Telescope spanning two decades to detect seven fast-moving stars in the innermost region of Omega Centauri, the largest and brightest globular cluster in the sky. These stars provide compelling new evidence for the presence of an intermediate-mass black hole; Omega Centauri is visible from Earth with the naked eye and is one of the favourite celestial objects for stargazers in the southern hemisphere. Although the cluster is 17 700 light-years away, lying just above the plane of the Milky Way, it appears almost as large as the full Moon when seen from a dark rural area. The exact classification of Omega Centauri has evolved through time, as our ability to study it has improved. It was first listed in Ptolemy’s catalogue nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677, and in the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster. Omega Centauri consists of roughly 10 million stars that are gravitationally bound. Credit: ESA/Hubble & NASA, M. Häberle (MPIA)
Omega Centauri consists of roughly 10 million stars that are gravitationally bound. An international team has now created an enormous catalogue of the motions of these stars, measuring the velocities for 1.4 million stars by studying over 500 Hubble images of the cluster. Most of these observations were intended to calibrate Hubble’s instruments rather than for scientific use, but they turned out to be an ideal database for the team’s research efforts. The extensive catalogue, which is the largest catalogue of motions for any star cluster to date, will be made openly available (more information is available here).
“We discovered seven stars that should not be there,” explained Maximilian Häberle of the Max Planck Institute for Astronomy in Germany, who led this investigation. “They are moving so fast that they should escape the cluster and never come back. The most likely explanation is that a very massive object is gravitationally pulling on these stars and keeping them close to the centre. The only object that can be so massive is a black hole, with a mass at least 8200 times that of our Sun.”
An international team of astronomers has used more than 500 images from the NASA/ESA Hubble Space Telescope spanning two decades to detect seven fast-moving stars in the innermost region of Omega Centauri, the largest and brightest globular cluster in the sky. These stars provide compelling new evidence for the presence of an intermediate-mass black hole (IMBH): this image shows the location of the IMBH in Omega Centauri. If confirmed, at its distance of 17 700 light-years the candidate black hole resides closer to Earth than the 4.3 million solar mass black hole in the centre of the Milky Way, which is 26 000 light-years away. Besides the Galactic centre, it would also be the only known case of a number of stars closely bound to a massive black hole. Credit: ESA/Hubble & NASA, M. Häberle (MPIA)
Several studies have suggested the presence of an IMBH in Omega Centauri [1]. However, other studies proposed that the mass could be contributed by a central cluster of stellar-mass black holes, and had suggested the lack of fast-moving stars above the necessary escape velocity made an IMBH less likely in comparison.
“This discovery is the most direct evidence so far of an IMBH in Omega Centauri,” added team lead Nadine Neumayer, also of the Max Planck Institute for Astronomy, who initiated the study with Anil Seth of the University of Utah in the United States. “This is exciting because there are only very few other black holes known with a similar mass. The black hole in Omega Centauri may be the best example of an IMBH in our cosmic neighbourhood.”
If confirmed, at its distance of 17 700 light-years the candidate black hole resides closer to Earth than the 4.3 million solar mass black hole in the centre of the Milky Way, which is 26 000 light-years away. Besides the Galactic centre, it would also be the only known case of a number of stars closely bound to a massive black hole.
The science team now hopes to characterise the black hole. While it is believed to measure at least 8200 solar masses, its exact mass and its precise position are not fully known. The team also intends to study the orbits of the fast-moving stars, which requires additional measurements of the respective line-of-sight velocities. The team has been granted time with the NASA/ESA/CSA James Webb Space Telescope to do just that, and also has other pending proposals to use other observatories.
Omega Centauri was also a recent feature of a new data release from ESA’s Gaia mission, which contained over 500 000 stars.
“Even after 30 years, the Hubble Space Telescope with its imaging instruments is still one of the best tools for high-precision astrometry in crowded stellar fields, regions where Hubble can provide added sensitivity from ESA’s Gaia mission observations,” shared team member Mattia Libralato of the National Institute for Astrophysics in Italy (INAF), and previously of AURA for the European Space Agency during the time of this study. “Our results showcase Hubble’s high resolution and sensitivity that are giving us exciting new scientific insights and will give a new boost to the topic of IMBHs in globular clusters.”
The results have been published online today in the journal Nature.
An international team of astronomers has used more than 500 images from the NASA/ESA Hubble Space Telescope spanning two decades to detect seven fast-moving stars in the innermost region of Omega Centauri, the largest and brightest globular cluster in the sky. These stars provide compelling new evidence for the presence of an intermediate-mass black hole; Omega Centauri is visible from Earth with the naked eye and is one of the favourite celestial objects for stargazers in the southern hemisphere. Although the cluster is 17 700 light-years away, lying just above the plane of the Milky Way, it appears almost as large as the full Moon when seen from a dark rural area. The exact classification of Omega Centauri has evolved through time, as our ability to study it has improved. It was first listed in Ptolemy’s catalogue nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677, and in the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster. Omega Centauri consists of roughly 10 million stars that are gravitationally bound. This image shows the central region of the Omega Centauri globular cluster, where the IMBH candidate was found. Credit: ESA/Hubble & NASA, M. Häberle (MPIA)
Notes
[1] In 2008, the Hubble Space Telescope and the Gemini Observatory found that the explanation behind Omega Centauri’s peculiarities may be a black hole hidden in its centre.
Astronomers find surprising shapes in Jupiter’s upper atmosphere, above the Great Red Spot
Using the NASA/ESA/CSA James Webb Space Telescope, scientists observed the region above Jupiter’s iconic Great Red Spot to discover a variety of previously unseen features. The region, previously believed to be unremarkable in nature, hosts a variety of intricate structures and activity.
New observations of the Great Red Spot on Jupiter have revealed that the planet’s atmosphere above and around the infamous storm is surprisingly interesting and active. This image shows the region observed by Webb’s Near-InfraRed Spectrograph (NIRSpec). It is stitched together from six NIRSpec Integral Field Unit images taken in July 2022, each around 300 square kilometres. The NIRSpec observations show infrared light emitted by hydrogen molecules in Jupiter’s ionosphere. These molecules lie over 300 kilometres above the clouds of the storm, where light from the Sun ionises the hydrogen and stimulates this infrared emission. In this image, redder colours display the hydrogen emission from these high altitudes in the planet’s ionosphere. Bluer colours show infrared light from lower altitudes, including cloud-tops in the atmosphere and the very prominent Great Red Spot. Jupiter is distant from the Sun and therefore receives a uniform, low level of daylight, meaning that most of the planet’s surface is relatively dim at these infrared wavelengths — especially compared to the emission from molecules near the poles, where Jupiter’s magnetic field is especially strong. Contrary to the researchers’ expectations that this area would therefore look homogeneous in nature, it hosts a variety of intricate structures, including dark arcs and bright spots, across the entire field of view. Credit: Credit: ESA/Webb, NASA & CSA, H. Melin, M. Zamani (ESA/Webb)
Jupiter is one of the brightest objects in the night sky, and it is easily seen on a clear night. Aside from the bright northern and southern lights at the planet’s polar regions, the glow from Jupiter’s upper atmosphere is weak and is therefore challenging for ground-based telescopes to discern details in this region. However, Webb’s infrared sensitivity allows scientists to study Jupiter’s upper atmosphere above the infamous Great Red Spot with unprecedented detail.
The upper atmosphere of Jupiter is the interface between the planet’s magnetic field and the underlying atmosphere. Here, the bright and vibrant displays of northern and southern lights can be seen, which are fuelled by the volcanic material ejected from Jupiter’s moon Io. However, closer to the equator, the structure of the planet’s upper atmosphere is influenced by incoming sunlight. Because Jupiter receives only 4% of the sunlight that is received on Earth, astronomers predicted this region to be homogeneous in nature.
New observations of the Great Red Spot on Jupiter have revealed that the planet’s atmosphere above and around the infamous storm is surprisingly interesting and active. This graphic shows the region observed by Webb — first its location on a NIRCam image of the whole planet (left), and the region itself (right), imaged by Webb’s Near-InfraRed Spectrograph (NIRSpec). The NIRSpec image is stitched together from six NIRSpec Integral Field Unit images taken in July 2022, each around 300 square kilometres, and shows infrared light emitted by hydrogen molecules in Jupiter’s ionosphere. These molecules lie over 300 kilometres above the clouds of the storm, where light from the Sun ionises the hydrogen and stimulates this infrared emission. In this image, redder colours display the hydrogen emission from these high altitudes in the planet’s ionosphere. Bluer colours show infrared light from lower altitudes, including cloud-tops in the atmosphere and the very prominent Great Red Spot. Jupiter is distant from the Sun and therefore receives a uniform, low level of daylight, meaning that most of the planet’s surface is relatively dim at these infrared wavelengths — especially compared to the emission from molecules near the poles, where Jupiter’s magnetic field is especially strong. Contrary to the researchers’ expectations that this area would therefore look homogeneous in nature, it hosts a variety of intricate structures, including dark arcs and bright spots, across the entire field of view. Credit: ESA/Webb, NASA & CSA, Jupiter ERS Team, J. Schmidt, H. Melin, M. Zamani (ESA/Webb)
The Great Red Spot of Jupiter was observed by Webb’s Near-InfraRed Spectrograph (NIRSpec) in July 2022, using the instrument’s Integral Field Unit capabilities. The team’s Early Release Science observations sought to investigate if this region was in fact dull, and the region above the iconic Great Red Spot was targeted for Webb’s observations. The team was surprised to discover that the upper atmosphere hosts a variety of intricate structures, including dark arcs and bright spots, across the entire field of view.
“We thought this region, perhaps naively, would be really boring,” shared team leader Henrik Melin of the University of Leicester in the United Kingdom. “It is in fact just as interesting as the northern lights, if not more so. Jupiter never ceases to surprise.”
Although the light emitted from this region is driven by sunlight, the team suggests there must be another mechanism altering the shape and structure of the upper atmosphere.
“One way in which you can change this structure is by gravity waves – similar to waves crashing on a beach, creating ripples in the sand,” explained Melin. “These waves are generated deep in the turbulent lower atmosphere, all around the Great Red Spot, and they can travel up in altitude, changing the structure and emissions of the upper atmosphere.”
The team explains that these atmospheric waves can be observed on Earth on occasion, however they are much weaker than those observed on Jupiter by Webb. They also hope to conduct follow-up Webb observations of these intricate wave patterns in the future to investigate how the patterns move within the planet’s upper atmosphere and to develop our understanding of the energy budget of this region and how the features change over time.
These findings may also support ESA’s Jupiter Icy Moons Explorer, Juice, which was launched on 14 April 2023. Juice will make detailed observations of Jupiter and its three large ocean-bearing moons — Ganymede, Callisto and Europa — with a suite of remote sensing, geophysical and in situ instruments. The mission will characterise these moons as both planetary objects and possible habitats, explore Jupiter’s complex environment in depth, and study the wider Jupiter system as an archetype for gas giants across the Universe.
These observations were taken as part of the Early Release Science programme #1373: ERS Observations of the Jovian System as a Demonstration of JWST’s Capabilities for Solar System Science (Co-PIs: I. de Pater, T. Fouchet).
“This ERS proposal was written back in 2017,” shared team member Imke de Pater of the University of California, Berkeley. “One of our objectives had been to investigate why the temperature above the Great Red Spot appeared to be high, as at the time recent observations with the NASA Infrared Telescope Facility had revealed. However, our new data showed very different results.”
These results have been published in Nature Astronomy.
An international team of astronomers have used the NASA/ESA/CSA James Webb Space Telescope to discover gravitationally bound star clusters when the Universe was 460 million years old. This is the first discovery of star clusters in an infant galaxy less than 500 million years after the Big bang.
An international team of astronomers have used the NASA/ESA/CSA James Webb Space Telescope to discover gravitationally bound star clusters when the Universe was 460 million years old. This is the first discovery of star clusters in an infant galaxy less than 500 million years after the Big bang. Young galaxies in the early Universe underwent significant burst phases of star formation, generating substantial amounts of ionising radiation. However, because of their cosmological distances, direct studies of their stellar content have proven challenging. Using Webb, an international team of astronomers have now detected five young massive star clusters in the Cosmic Gems arc (SPT0615-JD1), a strongly-lensed galaxy emitting light when the Universe was roughly 460 million years old, looking back across 97% of cosmic time. The Cosmic Gems arc was initially discovered in NASA/ESA Hubble Space Telescope images obtained by the RELICS (Reionization Lensing Cluster Survey) programme of the lensing galaxy cluster SPT-CL J0615−5746. With Webb, the science team can now see where stars formed and how they are distributed, in a similar way to how the Hubble Space Telescope is used to study local galaxies. Webb’s view provides a unique opportunity to study star formation and the inner workings of infant galaxies at such an unprecedented distance. Credit: ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration
Young galaxies in the early Universe underwent significant burst phases of star formation, generating substantial amounts of ionising radiation. However, because of their cosmological distances, direct studies of their stellar content have proven challenging. Using Webb, an international team of astronomers have now detected five young massive star clusters in the Cosmic Gems arc (SPT0615-JD1), a strongly-lensed galaxy emitting light when the Universe was roughly 460 million years old, looking back across 97% of cosmic time.
The Cosmic Gems arc was initially discovered in NASA/ESA Hubble Space Telescope images obtained by the RELICS (Reionization Lensing Cluster Survey) programme of the lensing galaxy cluster SPT-CL J0615−5746.
“These galaxies are thought to be a prime source of the intense radiation that reionised the early Universe,” shared lead author Angela Adamo of Stockholm University and the Oskar Klein Centre in Sweden. “What is special about the Cosmic Gems arc is that thanks togravitational lensingwe can actually resolve the galaxy down to parsec scales!”
An international team of astronomers have used the NASA/ESA/CSA James Webb Space Telescope to discover gravitationally bound star clusters when the Universe was 460 million years old. This is the first discovery of star clusters in an infant galaxy less than 500 million years after the Big bang. Young galaxies in the early Universe underwent significant burst phases of star formation, generating substantial amounts of ionising radiation. However, because of their cosmological distances, direct studies of their stellar content have proven challenging. Using Webb, an international team of astronomers have now detected five young massive star clusters in the Cosmic Gems arc (SPT0615-JD1), a strongly-lensed galaxy emitting light when the Universe was roughly 460 million years old, looking back across 97% of cosmic time. The Cosmic Gems arc was initially discovered in NASA/ESA Hubble Space Telescope images obtained by the RELICS (Reionization Lensing Cluster Survey) programme of the lensing galaxy cluster SPT-CL J0615−5746. With Webb, the science team can now see where stars formed and how they are distributed, in a similar way to how the Hubble Space Telescope is used to study local galaxies. Webb’s view provides a unique opportunity to study star formation and the inner workings of infant galaxies at such an unprecedented distance. Credit: ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration
With Webb, the science team can now see where stars formed and how they are distributed, in a similar way to how the Hubble Space Telescope is used to study local galaxies. Webb’s view provides a unique opportunity to study star formation and the inner workings of infant galaxies at such an unprecedented distance.
“Webb’s incredible sensitivity and angular resolution at near-infrared wavelengths, combined with gravitational lensing provided by the massive foreground galaxy cluster, enabled this discovery,” explained Larry Bradley of the Space Telescope Science Institute and PI of the Webb observing programme that captured these data.”No other telescope could have made this discovery.”
“The surprise and astonishment was incredible when we opened the Webb images for the first time,” added Adamo. “We saw a little chain of bright dots, mirrored from one side to the other — these cosmic gems are star clusters! Without Webb we would not have known we were looking at star clusters in such a young galaxy!”
In our Milky Way we see ancient globular clusters of stars, which are bound by gravity and have survived for billions of years. These are old relics of intense star formation in the early Universe, but it is not well understood where and when these clusters formed. The detection of massive young star clusters in the Cosmic Gems arc provides us with an excellent view of the early stages of a process that may go on to form globular clusters. The newly detected clusters in the arc are massive, dense and located in a very small region of their galaxy, but they also contribute the majority of the ultraviolet light coming from their host galaxy. The clusters are significantly denser than nearby star clusters. This discovery will help scientists to better understand how infant galaxies formed their stars and where globular clusters formed.
An international team of astronomers have used the NASA/ESA/CSA James Webb Space Telescope to discover gravitationally bound star clusters when the Universe was 460 million years old. This is the first discovery of star clusters in an infant galaxy less than 500 million years after the Big bang. Young galaxies in the early Universe underwent significant burst phases of star formation, generating substantial amounts of ionising radiation. However, because of their cosmological distances, direct studies of their stellar content have proven challenging. Using Webb, an international team of astronomers have now detected five young massive star clusters in the Cosmic Gems arc (SPT0615-JD1), a strongly-lensed galaxy emitting light when the Universe was roughly 460 million years old, looking back across 97% of cosmic time. The Cosmic Gems arc was initially discovered in NASA/ESA Hubble Space Telescope images obtained by the RELICS (Reionization Lensing Cluster Survey) programme of the lensing galaxy cluster SPT-CL J0615−5746. With Webb, the science team can now see where stars formed and how they are distributed, in a similar way to how the Hubble Space Telescope is used to study local galaxies. Webb’s view provides a unique opportunity to study star formation and the inner workings of infant galaxies at such an unprecedented distance. Credit: ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration
The team notes that this discovery connects a variety of scientific fields.
“These results provide direct evidence that indicates proto-globular clusters formed in faint galaxies during the reionisation era, which contributes to our understanding of how these galaxies have succeeded in reionising the Universe,” explained Adamo. “This discovery also places important constraints on the formation of globular clusters and their initial properties. For instance, the high stellar densities found in the clusters provide us with the first indication of the processes taking place in their interiors, giving new insights into the possible formation of very massive stars and black hole seeds, which are both important for galaxy evolution.”
In the future, the team hopes to build a sample of galaxies for which similar resolutions can be achieved.
“I am confident there are other systems like this waiting to be uncovered in the early Universe, enabling us to further our understanding of early galaxies,”
said Eros Vanzella from the INAF – Astrophysics and Space Science Observatory of Bologna (OAS), Italy, one of the main contributors to the work.
An international team of astronomers have used the NASA/ESA/CSA James Webb Space Telescope to discover gravitationally bound star clusters when the Universe was 460 million years old. This is the first discovery of star clusters in an infant galaxy less than 500 million years after the Big bang. Young galaxies in the early Universe underwent significant burst phases of star formation, generating substantial amounts of ionising radiation. However, because of their cosmological distances, direct studies of their stellar content have proven challenging. Using Webb, an international team of astronomers have now detected five young massive star clusters in the Cosmic Gems arc (SPT0615-JD1), a strongly-lensed galaxy emitting light when the Universe was roughly 460 million years old, looking back across 97% of cosmic time. The Cosmic Gems arc was initially discovered in NASA/ESA Hubble Space Telescope images obtained by the RELICS (Reionization Lensing Cluster Survey) programme of the lensing galaxy cluster SPT-CL J0615−5746. With Webb, the science team can now see where stars formed and how they are distributed, in a similar way to how the Hubble Space Telescope is used to study local galaxies. Webb’s view provides a unique opportunity to study star formation and the inner workings of infant galaxies at such an unprecedented distance. Credit: ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration
In the meantime, the team is preparing for further observations and spectroscopy with Webb.
“We plan to study this galaxy with Webb’s NIRSpec and MIRI instruments in Cycle 3,” added Bradley. “The NIRSpec observations will allow us to confirm the redshift of the galaxy and to study the ultraviolet emission of the star clusters, which will be used to study their physical properties in more detail. The MIRI observations will allow us to study the properties of ionised gas. The spectroscopic observations will also allow us to spatially map the star formation rate.”
These results have been published today in Nature. The data for this result were captured under Webb observing programme #4212 (PI: L. Bradley).
An international team of astronomers have used the NASA/ESA/CSA James Webb Space Telescope to discover gravitationally bound star clusters when the Universe was 460 million years old. This is the first discovery of star clusters in an infant galaxy less than 500 million years after the Big bang. Young galaxies in the early Universe underwent significant burst phases of star formation, generating substantial amounts of ionising radiation. However, because of their cosmological distances, direct studies of their stellar content have proven challenging. Using Webb, an international team of astronomers have now detected five young massive star clusters in the Cosmic Gems arc (SPT0615-JD1), a strongly-lensed galaxy emitting light when the Universe was roughly 460 million years old, looking back across 97% of cosmic time. The Cosmic Gems arc was initially discovered in NASA/ESA Hubble Space Telescope images obtained by the RELICS (Reionization Lensing Cluster Survey) programme of the lensing galaxy cluster SPT-CL J0615−5746. With Webb, the science team can now see where stars formed and how they are distributed, in a similar way to how the Hubble Space Telescope is used to study local galaxies. Webb’s view provides a unique opportunity to study star formation and the inner workings of infant galaxies at such an unprecedented distance. Credit: ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration
Bibliographic information:
Angela Adamo, Larry D. Bradley, Eros Vanzella, Adélaïde Claeyssens, Brian Welch4, Jose M Diego, Guillaume Mahler, Masamune Oguri, Keren Sharon, Abdurro’uf, Tiger Yu-Yang Hsiao, Xinfeng Xu, Matteo Messa, Augusto E. Lassen, Erik Zackrisson, Gabriel Brammer, Dan Coe, Vasily Kokorev, Massimo Ricotti, Adi Zitrin, Seiji Fujimoto, Akio K. Inoue, Tom Resseguier, Jane R. Rigby, Yolanda Jiménez-Teja, Rogier A. Windhorst, Takuya Hashimoto and Yoichi Tamura, Bound star clusters observed in a lensed galaxy 460 Myr after the Big Bang, Nature.
First of its kind detection made in striking new Webb image: alignment of bipolar jets confirms star formation theories in Serpens Nebula
For the first time, a phenomenon astronomers have long hoped to image directly has been captured by the NASA/ESA/CSA James Webb Space Telescope’s Near-InfraRed Camera (NIRCam). In this stunning image of the Serpens Nebula, the discovery lies in the northern area of this young, nearby star-forming region.
In this image of the Serpens Nebula from the Near-InfraRed Camera (NIRCam) on the NASA/ESA/CSA James Webb Space Telescope, astronomers found a grouping of aligned protostellar outflows within one small region (the top left corner). In the Webb image, these jets are identified by bright red clumpy streaks, which are shockwaves caused when the jet hits the surrounding gas and dust. The Serpens Nebula, located 1 300 light-years from Earth, is home to a particularly dense cluster of newly forming stars (around 100 000 years old), some of which will eventually grow to the mass of our Sun. This region has been home to other coincidental discoveries, including the flapping ‘Bat Shadow’, which earned its name when 2020 data from the NASA/ESA Hubble Space Telescope revealed it to flap, or shift. This feature is visible at the centre of the Webb image. To the right of the ‘Bat Shadow’ lies another intriguing feature—an eye-shaped crevice, which appears as if a star is bursting through. However, astronomers say looks may be deceiving here. This could just be where gases of different densities are layered on top of one another, similar to what is seen in the famous Pillars of Creation. And to the right of that, an extremely dark patch could be a similar occurrence. The gas and dust here are so dense in comparison to the rest of the region that no near-infrared light is getting through. Credit: NASA, ESA, CSA, STScI, K. Pontoppidan (NASA’s Jet Propulsion Laboratory), J. Green (Space Telescope Science Institute)
The astronomers found an intriguing group of protostellar outflows, formed when jets of gas spewing from newborn stars collide with nearby gas and dust at high speeds. Typically these objects have a variety of orientations within one region. Here, however, they are all slanted in the same direction, to the same degree, like sleet pouring down during a storm.
The discovery of these aligned objects, made possible only by Webb’s exquisite spatial resolution and sensitivity at near-infrared wavelengths, is providing information about the fundamentals of how stars are born.
So just how does the alignment of the stellar jets relate to the rotation of the star? As an interstellar gas cloud collapses in on itself to form a star, it spins more rapidly. The only way for the gas to continue moving inward is for some of the spin (known as angular momentum) to be removed. A disc of material forms around the young star to transport material down, like a whirlpool around a drain. The swirling magnetic fields in the inner disc launch some of the material into twin jets that shoot outward in opposite directions, perpendicular to the disc of material.
In the Webb image, these jets are identified by bright red clumpy streaks, which are shockwaves caused when the jet hits the surrounding gas and dust. Here, the red colour indicates the presence of molecular hydrogen and carbon monoxide. Webb can image these extremely young stars and their outflows, which were previously obstructed at optical wavelengths.
Astronomers say there are a few forces that potentially can shift the direction of the outflows during this period of a young star’s life. One way is when binary stars spin around each other and wobble in orientation, twisting the direction of the outflows over time.
Stars of the Serpens Nebula
This image shows the centre of the Serpens Nebula as seen by the NASA/ESA/CSA James Webb Space Telescope’s Near-InfraRed Camera (NIRCam). The Serpens Nebula, located 1300 light-years from Earth, is home to a particularly dense cluster of newly forming stars (about 100 000 years old), some of which will eventually grow to the mass of our Sun. Webb’s image of this nebula revealed a grouping of aligned protostellar outflows (seen in the top left). These jets are identified by bright clumpy streaks that appear red, which are shock waves caused when the jet hits the surrounding gas and dust. Throughout this image filaments and wisps of different hues represent reflected starlight from still-forming protostars within the cloud. In some areas, there is dust in front of that reflection, which appears here in an orange, diffuse shade. Credit: NASA, ESA, CSA, STScI, K. Pontoppidan (NASA’s Jet Propulsion Laboratory), J. Green (Space Telescope Science Institute)
The Serpens Nebula is only one or two million years old, which is very young in cosmic terms. It’s also home to a particularly dense cluster of newly forming stars (around 100 000 years old) at the centre of this image, some of which will eventually grow to the mass of our Sun.
Serpens is a reflection nebula, which means it’s a cloud of gas and dust that does not create its own light but instead shines by reflecting the light from stars close to or within the nebula.
So, throughout the region in this image, filaments and wisps of different hues represent reflected starlight from still-forming protostars within the cloud. In some areas there is dust in front of that reflection, which appears here in an orange, diffuse shade.
This image from the NASA/ESA/CSA James Webb Space Telescope shows a portion of the Serpens Nebula, where astronomers have discovered a grouping of aligned protostellar outflows. These jets are signified by bright clumpy streaks that appear red, which are shock waves from the jet hitting surrounding gas and dust. Here, the red colour represents the presence of molecular hydrogen and carbon monoxide. Typically these objects have a variety of orientations within one region. Here, however, they are all slanted in the same direction, to the same degree, like sleet pouring down during a storm. Researchers say the discovery of these aligned objects, made possible only by Webb’s exquisite spatial resolution and sensitivity at near-infrared wavelengths, is providing information about the fundamentals of how stars are born. Credit: NASA, ESA, CSA, STScI, K. Pontoppidan (NASA’s Jet Propulsion Laboratory), J. Green (Space Telescope Science Institute)
This region has been home to other coincidental discoveries, including the flapping ‘Bat Shadow’, which earned its name when 2020 data from the NASA/ESAHubble Space Space Telescope revealed it to flap, or shift. This feature is visible at the centre of the Webb image.
Future studies
The stunning image and the serendipitous discovery of the aligned objects are actually just the first step in this scientific programme. The team will now use Webb’s NIRSpec (Near-InfraRed Spectrograph) to investigate the chemical make-up of the cloud.
Astronomers are interested in determining how volatile chemicals survive star and planet formation. Volatiles are compounds that sublimate, or transition from a solid directly to a gas, at a relatively low temperature — including water and carbon monoxide. They’ll then compare their findings to the amounts found in protoplanetary discs of similar-type stars.
These observations were made as part of the Webb General Observer programme 1611 (PI: K. Pontoppidan). The team’s initial results have been published in the Astrophysical Journal.
This image of the Serpens Nebula, captured by Webb’s Near-InfraRed Camera (NIRCam), shows compass arrows, a scale bar and a colour key for reference. The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to the direction of arrows on a map of the ground (as seen from above). The scale bar is labelled in light-years, which is the distance that light travels in one Earth-year. One light-year is equal to about 9.46 trillion kilometres, or 5.88 trillion miles. This image shows invisible near-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which NIRCam filters were used when collecting the light. The colour of each filter name is the visible light colour used to represent the infrared light that passes through that filter. Credit: NASA, ESA, CSA, STScI, K. Pontoppidan (NASA’s Jet Propulsion Laboratory), J. Green (Space Telescope Science Institute)
Investigating the origins of the Crab Nebula with Webb
New data revise our view of this unusual supernova explosion.
The Crab Nebula is a nearby example of the debris left behind when a star undergoes a violent death in a supernova explosion. However, despite decades of study, this supernova remnant continues to maintain a degree of mystery: what type of star was responsible for the creation of the Crab Nebula, and what was the nature of the explosion? The NASA/ESA/CSA James Webb Space Telescope has provided a new view of the Crab, including the highest-quality infrared data yet available to aid scientists as they explore the detailed structure and chemical composition of the remnant. These clues are helping to unravel the unusual way that the star exploded about 1000 years ago.
Image of the Crab Nebula captured by Webb’s NIRCam and MIRI, with compass arrows, scale bar, and colour key for reference. The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above). The scale bar is labelled in light-years, which is the distance that light travels in one Earth-year. (It takes two years for light to travel a distance equal to the length of the bar.) One light-year is equal to about 9.46 trillion kilometres or 5.88 trillion miles. The field of view shown in this image is approximately 10 light-years across. This image shows invisible near-infrared and mid-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which components were observed by NIRCam and MIRI, and which visible-light colour is assigned to each feature. Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University)
A team of scientists used the NASA/ESA/CSA James Webb Space Telescope to parse the composition of the Crab Nebula, a supernova remnant located 6500 light-years away in the constellation Taurus. With the telescope’s MIRI (Mid-Infared Instrument) and NIRCam (Near-Infrared Camera), the team gathered data that are helping to clarify the Crab Nebula’s history.
The Crab Nebula is the result of a core-collapse supernova that was the death of a massive star. The supernova explosion itself was seen on Earth in 1054 CE and was bright enough to view during the daytime. The much fainter remnant observed today is an expanding shell of gas and dust, and an outflowing wind powered by a pulsar, a rapidly spinning and highly magnetised neutron star.
The Crab Nebula is also highly unusual. Its atypical composition and very low explosion energy have previously led astronomers to think it was an electron-capture supernova — a rare type of explosion that arises from a star with a less-evolved core made of oxygen, neon, and magnesium, rather than a more typical iron core.
Past research efforts have calculated the total kinetic energy of the explosion based on the quantity and velocities of the present-day ejecta. Astronomers deduced that the nature of the explosion was one of relatively low energy (less than one-tenth that of a normal supernova), and the progenitor star’s mass was in the range of eight to 10 solar masses — teetering on the thin line between stars that experience a violent supernova death and those that do not.
However, inconsistencies exist between the electron-capture supernova theory and observations of the Crab, particularly the observed rapid motion of the pulsar. In recent years, astronomers have also improved their understanding of iron-core-collapse supernovae and now think that this type can also produce low-energy explosions, providing the stellar mass is adequately low.
To lower the level of uncertainty about the Crab’s progenitor star and the nature of the explosion, the science team used Webb’s spectroscopic capabilities to home in on two areas located within the Crab’s inner filaments.
Theories predict that because of the different chemical composition of the core in an electron-capture supernova, the nickel to iron (Ni/Fe) abundance ratio should be much higher than the ratio measured in our Sun (which contains these elements from previous generations of stars). Studies in the late 1980s and early 1990s measured the Ni/Fe ratio within the Crab using optical and near-infrared data and noted a high Ni/Fe abundance ratio that seemed to favour the electron-capture supernova scenario.
The Webb telescope, with its sensitive infrared capabilities, is now advancing Crab Nebula research. The team used MIRI’s spectroscopic abilities to measure the nickel and iron emission lines, resulting in a more reliable estimate of the Ni/Fe abundance ratio. They found that the ratio was still elevated compared to the Sun, but only modestly so and much lower in comparison to earlier estimates.
The revised values are consistent with electron-capture, but do not rule out an iron-core-collapse explosion from a similarly low-mass star. (Higher-energy explosions from higher-mass stars are expected to produce Ni/Fe ratios closer to solar abundances.) Further observational and theoretical work will be needed to distinguish between these two possibilities.
Besides pulling spectral data from two small regions of the Crab Nebula’s interior to measure the abundance ratio, the telescope also observed the remnant’s broader environment to understand details of the synchrotron emission and the dust distribution.
The images and data collected by MIRI enabled the team to isolate the dust emission within the Crab and map it in high resolution for the first time. By mapping the warm dust emission with Webb, and even combining it with the Herschel Space Observatory’s data on cooler dust grains, the team created a well-rounded picture of the dust distribution: the outermost filaments contain relatively warmer dust, while cooler grains are prevalent near the centre.
The observations were taken as part of the Webb General Observer programme 1714.
The NASA/ESA/CSA James Webb Space Telescope dissected the Crab Nebula’s structure, aiding astronomers as they continue to evaluate leading theories about the supernova remnant’s origins. With the data collected by Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument), a team of scientists were able to closely inspect some of the Crab Nebula’s major components. For the first time ever, astronomers mapped the warm dust emission throughout this supernova remnant. Represented here as fluffy magenta material, the dust grains form a cage-like structure that is most apparent toward the lower left and upper right portions of the remnant. Filaments of dust are also threaded throughout the Crab’s interior and sometimes coincide with regions of doubly ionised sulphur (sulphur III), coloured in green. Yellow-white mottled filaments, which form large loop-like structures around the supernova remnant’s centre, represent areas where dust and doubly ionised sulphur overlap. The dust’s cage-like structure helps constrain some, but not all of the ghostly synchrotron emission represented in blue. The emission resembles wisps of smoke, most notable toward the Crab’s centre. The thin blue ribbons follow the magnetic field lines created by the Crab’s pulsar heart — a rapidly rotating neutron star. Credit: NASA, ESA, CSA, STScI, T. Temim (Princeton University)
Webb finds plethora of carbon molecules around ISO-ChaI 147, a young star
An international team of astronomers have used the NASA/ESA/Webb James Webb Space Telescope to study the disc around a young and very low-mass star. The results reveal the richest hydrocarbon chemistry seen to date in a protoplanetary disc (including the first extrasolar detection of ethane) and contribute to our evolving understanding of the diversity of planetary systems.
This is an artist’s impression of a young star surrounded by a protoplanetary disc. An international team of astronomers have used the NASA/ESA/Webb James Webb Space Telescope to study the disc around a young and very low-mass star. The results reveal the richest hydrocarbon chemistry seen to date in a protoplanetary disc (including the first extrasolar detection of ethane) and contribute to our evolving understanding of the diversity of planetary systems. The science team explored the region around a very low-mass star of 0.11 solar masses (known as ISO-ChaI 147). These observations provide insights into the environment as well as basic ingredients for such planets to form. The team found that the gas in the planet-forming region of the star is rich in carbon. This could potentially be because carbon is removed from the solid material from which rocky planets can form, and could explain why Earth is relatively carbon-poor. Credit: NASA/JPL-Caltech
Planets form in discs of gas and dust orbiting young stars. Observations indicate that terrestrial planets are expected to form more efficiently than gas giants in the discs around very low-mass stars. While very low-mass stars have the highest rate of occurrence of orbiting rocky planets, their planetary compositions are largely unknown. For example, the Trappist-1 system (which Webb has studied) consists of seven rocky planets within 0.1 au [1] and their composition is generally assumed to be Earth-like. However, new data from Webb suggests that discs around very low-mass stars may evolve differently from those around more massive stars.
The MIRI Mid-INfrared Disk Survey (MINDS) aims to build a bridge between the chemical inventory of discs and the properties of exoplanets. In a new study, this team explored the region around a very low-mass star of 0.11 solar masses (known as ISO-ChaI 147). These observations provide insights into the environment as well as basic ingredients for such planets to form. The team found that the gas in the planet-forming region of the star is rich in carbon. This could potentially be because carbon is removed from the solid material from which rocky planets can form, and could explain why Earth is relatively carbon-poor.
“Webb has a better sensitivity and spectral resolution than previous infrared space telescopes,” explained lead author Aditya Arabhavi of the University of Groningen in the Netherlands. “These observations are not possible from Earth, because the emissions are blocked by the atmosphere. Previously we could only identify acetylene (C2H2) emission from this object. However, Webb’s higher sensitivity and spectral resolution allowed us to detect weak emission from less abundant molecules. Webb also allowed us to understand that these hydrocarbon molecules are not just diverse but also abundant.”
This graphic presents some of the results from the MIRI Mid-INfrared Disk Survey (MINDS), which aims to build a bridge between the chemical inventory of discs and the properties of exoplanets. In a new study, the science team explored the region around a very low-mass star of 0.11 solar masses (known as ISO-ChaI 147). These observations provide insights into the environment as well as basic ingredients for such planets to form. The team found that the gas in the planet-forming region of the star is rich in carbon. This could potentially be because carbon is removed from the solid material from which rocky planets can form, and could explain why Earth is relatively carbon-poor. The spectrum revealed by Webb’s Mid-InfraRed Instrument (MIRI) shows the richest hydrocarbon chemistry seen to date in a protoplanetary disc, consisting of 13 carbon-bearing molecules up to benzene. This includes the first extrasolar detection of ethane (C2H6), the largest fully-saturated hydrocarbon detected outside our Solar System. Since fully-saturated hydrocarbons are expected to form from more basic molecules, detecting them here gives researchers clues about the chemical environment. The team also successfully detected ethylene (C2H4), propyne (C3H4), and the methyl radical CH3, for the first time in a protoplanetary disc. This graphic highlights the detections of ethane (C2H6), methane (CH4), propyne (C3H4), cyanoacetylene (HC3N), and the methyl radical CH3. Credit: NASA, ESA, CSA, R. Crawford (STScI)
The spectrum revealed by Webb’s Mid-InfraRed Instrument (MIRI) shows the richest hydrocarbon chemistry seen to date in a protoplanetary disc, consisting of 13 carbon-bearing molecules up to benzene. This includes the first extrasolar detection of ethane (C2H6), the largest fully-saturated hydrocarbon [2] detected outside our Solar System. Since fully-saturated hydrocarbons are expected to form from more basic molecules, detecting them here gives researchers clues about the chemical environment. The team also successfully detected ethylene (C2H4), propyne (C3H4), and the methyl radical CH3, for the first time in a protoplanetary disc.
“These molecules have already been detected in our Solar System, for example in comets such as 67P/Churyumov–Gerasimenko and C/2014 Q2 (Lovejoy),” adds Arabhavi. “It is amazing that we can now see the dance of these molecules in the planetary cradles. It is a very different planet-forming environment from what we usually think of.”
The team indicates that these results have large implications for astrochemistry in the inner 0.1 au and the planets forming there. “This is profoundly different from the composition we see in discs around solar-type stars, where oxygen bearing molecules dominate (like carbon dioxide and water),” added team member Inga Kamp, also of the University of Groningen. “This object establishes that these are a unique class of objects.”
“It’s incredible that we can detect and quantify the amount of molecules that we know well on Earth, such as benzene, in an object that is more than 600 light-years away,” added team member Agnés Perrin of Centre National de la Recherche Scientifique in France.
Next, the science team intend to expand their study to a larger sample of such discs around very low-mass stars to develop their understanding of how common such exotic carbon-rich terrestrial planet forming regions are. “The expansion of our study will also allow us to better understand how these molecules can form,” explained team member and PI of the MINDS programme, Thomas Henning, of the Max Planck Institute for Astronomy in Germany. “Several features in the Webb data are also still unidentified, so more spectroscopy is required to fully interpret our observations.”
This work also highlights the crucial need for scientists to collaborate across disciplines. The team notes that these results and the accompanying data can contribute towards other fields including theoretical physics, chemistry and astrochemistry, to interpret the spectra and to investigate new features in this wavelength range.
These results have been published in the journal Science.
Notes
[1] An astronomical unit (AU, or au) is a unit of length effectively equal to the average, or mean, distance between Earth and the Sun, which is defined as roughly 150 million kilometres.
[2] Saturated hydrocarbons are molecules that are made entirely of single carbon-carbon bonds. They cannot incorporate additional atoms into their structure, and are therefore said to be saturated.
Webb detects most distant black hole merger to date in the ZS7 galaxy system
An international team of astronomers have used the NASA/ESA/CSA James Webb Space Telescope to find evidence for an ongoing merger of two galaxies and their massive black holes when the Universe was only 740 million years old. This marks the most distant detection of a black hole merger ever obtained and the first time that this phenomenon has been detected so early in the Universe.
This image shows the location of the galaxy system ZS7 from the JWST PRIMER programme (PI: J. Dunlop). New research using the NIRSpec instrument on the NASA/ESA/CSA James Webb Space Telescope have determined the system to be evidence of an ongoing merger of two galaxies and their massive black holes when the Universe was only 740 million years old. This marks the most distant detection of a black hole merger ever obtained and the first time that this phenomenon has been detected so early in the Universe. The team has found evidence for very dense gas with fast motions in the vicinity of the black hole, as well as hot and highly ionised gas illuminated by the energetic radiation typically produced by black holes in their accretion episodes. Webb also allowed the team to spatially separate the two black holes and determined that one of the two black holes has a mass that is 50 million times the mass of the Sun. The mass of the other black hole is likely similar, although it is harder to measure because this second black hole is buried in dense gas. In this Webb NIRCam image, the ionised hydrogen (Hβ) emission in the ZS7 system is identified by the orange region and the doubly ionised oxygen (OIII) emission is visible in dark red (right image). Credit: ESA/Webb, NASA, CSA, J. Dunlop, D. Magee, P. G. Pérez-González, H. Übler, R. Maiolino, et al.
Astronomers have found supermassive black holes with masses of millions to billions times that of the Sun in most massive galaxies in the local Universe, including in our Milky Way galaxy. These black holes have likely had a major impact on the evolution of the galaxies they reside in. However, scientists still don’t fully understand how these objects grew to become so massive. The finding of gargantuan black holes already in place in the first billion years after the Big Bang indicates that such growth must have happened very rapidly, and very early. Now, the James Webb Space Telescope is shedding new light on the growth of black holes in the early Universe.
The new Webb observations have provided evidence for an ongoing merger of two galaxies and their massive black holes when the Universe was just 740 million years old. The system is known as ZS7.
Massive black holes that are actively accreting matter have distinctive spectrographic features that allow astronomers to identify them. For very distant galaxies, like those in this study, these signatures are inaccessible from the ground and can only be seen with Webb.
“We found evidence for very dense gas with fast motions in the vicinity of the black hole, as well as hot and highly ionised gas illuminated by the energetic radiation typically produced by black holes in their accretion episodes,” explained lead author Hannah Übler of the University of Cambridge in the United Kingdom. “Thanks to the unprecedented sharpness of its imaging capabilities, Webb also allowed our team to spatially separate the two black holes.”
The team found that one of the two black holes has a mass that is 50 million times the mass of the Sun.
“The mass of the other black hole is likely similar, although it is much harder to measure because this second black hole is buried in dense gas,”
explained team member Roberto Maiolino of the University of Cambridge and University College London in the United Kingdom.
“Our findings suggest that merging is an important route through which black holes can rapidly grow, even at cosmic dawn,” explained Übler. “Together with other Webb findings of active, massive black holes in the distant Universe, our results also show that massive black holes have been shaping the evolution of galaxies from the very beginning.”
“The stellar mass of the system we studied is similar to that of our neighbor the Large Magellanic Cloud,” shared team member Pablo G. Pérez-González of the Centro de Astrobiología (CAB), CSIC/INTA, in Spain. “We can try to imagine how the evolution of merging galaxies could be affected if each galaxy had one super massive black hole as large or larger than the one we have in the Milky Way”.
This image shows the environment of the galaxy system ZS7 from the JWST PRIMER programme (PI: J. Dunlop) as seen by Webb’s NIRCam instrument. New research using the NIRSpec instrument on the NASA/ESA/CSA James Webb Space Telescope has determined the system to be evidence of an ongoing merger of two galaxies and their massive black holes when the Universe was only 740 million years old. This marks the most distant detection of a black hole merger ever obtained and the first time that this phenomenon has been detected so early in the Universe. The team has found evidence for very dense gas with fast motions in the vicinity of the black hole, as well as hot and highly ionised gas illuminated by the energetic radiation typically produced by black holes in their accretion episodes. Webb also allowed the team to spatially separate the two black holes and determined that one of the two black holes has a mass that is 50 million times the mass of the Sun. The mass of the other black hole is likely similar, although it is harder to measure because this second black hole is buried in dense gas. Credit: ESA/Webb, NASA, CSA, J. Dunlop, D. Magee, P. G. Pérez-González, H. Übler, R. Maiolino, et al.
The team also notes that once the two black holes merge, they will also generate gravitational waves [1]. Events like this will be detectable with the next generation of gravitational wave observatories, such as the upcoming Laser Interferometer Space Antenna (LISA) mission, which was recently approved by the European Space Agency and will be the first space-based observatory dedicated to studying gravitational waves.
“Webb’s results are telling us that lighter systems detectable by LISA should be far more frequent than previously assumed,” shared LISA Lead Project Scientist Nora Luetzgendorf of the European Space Agency in the Netherlands. “It will most likely make us adjust our models for LISA rates in this mass range. This is just the tip of the iceberg.”
This discovery was from observations made as part of the Galaxy Assembly with NIRSpec Integral Field Spectroscopy programme. The team has recently been awarded a new Large Programme in Webb’s Cycle 3 of observations, to study in detail the relationship between massive black holes and their host galaxies in the first billion years. An important component of this programme will be to systematically search for and characterise black hole mergers. This effort will determine the rate at which black hole merging occurs at early cosmic epochs and will assess the role of merging in the early growth of black holes and the rate at which gravitational waves are produced from the dawn of time.
These results have been published in the Monthly Notices of the Royal Astronomical Society.
Notes
[1] Gravitational waves are invisible ripples in the fabric of spacetime. Spacetime is a four-dimensional quantity, described by Einstein’s general theory of relativity, which fuses three-dimensional space with time. Mass warps spacetime, and gravity is actually the result of spacetime being curved by an object’s mass. Ripples through spacetime are created by the movement of any object with mass, and these are known as gravitational waves. Gravitational waves are constantly passing unnoticed through Earth and they are caused by some of the most violent and energetic events in the Universe. These include colliding black holes, collapsing stellar cores, merging neutron stars or white dwarf stars, the wobble of neutron stars that are not perfect spheres and possibly even the remnants of gravitational radiation created at the birth of the Universe.
