Webb finds candidates for first young brown dwarfs outside the Milky Way, in the star cluster NGC 602
An international team of astronomers has used the NASA/ESA/CSA James Webb Space Telescope to detect the first rich population of brown dwarf candidates outside the Milky Way in the star cluster NGC 602.
Near the outskirts of the Small Magellanic Cloud, a satellite galaxy roughly 200 000 light-years from Earth, lies the young star cluster NGC 602. The local environment of this cluster is a close analogue of what existed in the early Universe, with very low abundances of elements heavier than hydrogen and helium. The existence of dark clouds of dense dust and the fact that the cluster is rich in ionised gas also suggest the presence of ongoing star formation processes. Together with its associated HII [1] region N90, which contains clouds of ionised atomic hydrogen, this cluster provides a valuable opportunity to examine star formation scenarios under dramatically different conditions from those in the solar neighbourhood.
An international team of astronomers, including Peter Zeidler, Elena Sabbi, Elena Manjavacas and Antonella Nota, used Webb to observe NGC 602 and they detected candidates for the first young brown dwarfs outside our Milky Way.
“Only with the incredible sensitivity and spatial resolution in the correct wavelength regime is it possible to detect these objects at such great distances,” shared lead author Peter Zeidler of AURA/STScI for the European Space Agency. “This has never been possible before and also will remain impossible from the ground for the foreseeable future.”
Brown dwarfs are the more massive cousins of giant gas planets (typically ranging from roughly 13 to 75 Jupiter masses, and sometimes lower). They are free-floating, meaning that they are not gravitationally bound to a star as exoplanets are. However, some of them share characteristics with exoplanets, like their atmospheric composition and storm patterns.
“Until now, we’ve known of about 3000 brown dwarfs, but they all live inside our own galaxy,” added team member Elena Manjavacas of AURA/STScI for the European Space Agency.
“This discovery highlights the power of using both Hubble and Webb to study young stellar clusters,” explained team member Antonella Nota, executive director of the International Space Science Institute in Switzerland and the previous Webb Project Scientist for ESA. “Hubble showed that NGC602 harbors very young low mass stars, but only with Webb we can finally see the extent and the significance of the substellar mass formation in this cluster. Hubble and Webb are an amazingly powerful telescope duo!”
“Our results fit very well with the theory that the mass distribution of bodies below the hydrogen burning limit is simply a continuation of the stellar distribution,” shared Zeidler. “It seems they form in the same way, they just don’t accrete enough mass to become a fully fledged star.”
The team’s data include a new image from Webb’s Near-InfraRed Camera (NIRCam) of NGC 602, which highlights the cluster stars, the young stellar objects, and the surrounding gas and dust ridges, as well as the gas and dust itself, while also showing the significant contamination by background galaxies and other stars in the Small Magellanic Cloud. These observations were made in April 2023.
“By studying the young metal-poor brown dwarfs newly discovered in NGC602, we are getting closer to unlocking the secrets of how stars and planets formed in the harsh conditions of the early Universe,“ added team member Elena Sabbi of NSF’s NOIRLab, the University of Arizona, and the Space Telescope Science Institute.
“These are the first substellar objects outside the Milky Way” added Manjavacas. “We need to be ready for new ground-breaking discoveries in these new objects!”
These observations were made as part of the JWST GO programme #2662 (PI: P. Zeidler). The results have been published in The Astrophysical Journal.
Near the outskirts of the Small Magellanic Cloud, a satellite galaxy roughly 200 000 light-years from Earth, lies the young star cluster NGC 602, which is featured in this new image from the NASA/ESA/CSA James Webb Space Telescope. This image includes data from Webb’s NIRCam (Near-InfraRed Camera) and MIRI (Mid-InfraRed Instrument). The local environment of this cluster is a close analogue of what existed in the early Universe, with very low abundances of elements heavier than hydrogen and helium. The existence of dark clouds of dense dust and the fact that the cluster is rich in ionised gas also suggest the presence of ongoing star formation processes. This cluster provides a valuable opportunity to examine star formation scenarios under dramatically different conditions from those in the solar neighbourhood. An international team of astronomers, including Peter Zeidler, Elena Sabbi, and Antonella Nota, used Webb to observe NGC 602 and detected candidates for the first young brown dwarfs outside our Milky Way. Credit: ESA/Webb, NASA & CSA, P. Zeidler, E. Sabbi, A. Nota, M. Zamani (ESA/Webb)
Notes
[1] Some of the most beautiful extended objects that we can see are known as HII regions, also called diffuse or emission nebulae. They contain mostly ionised hydrogen and are found throughout the interstellar medium in the Milky Way and in other galaxies.
The NASA/ESA Hubble Space Telescope has provided a dramatic and colourful close-up look at one of the most rambunctious stars in our galaxy, weaving a huge spiral pattern among the stars. Hubble’s images capture its details and its evolution is featured by a unique timelapse video.
Residing only roughly 700 light-years from Earth in the constellation Aquarius, R Aquarii is a symbiotic binary star: a type of binary star system consisting of a white dwarf and a red giant that is surrounded by a large, dynamic nebula. As the closest symbiotic star to Earth, R Aquarii was studied by none other than Edwin Hubble in an effort to understand the mechanism that powers the system.
R Aquarii undergoes violent eruptions that blast out huge filaments of glowing gas. This dramatically demonstrates how the Universe redistributes the products of nuclear energy that form deep inside stars and jet back into space.
R Aquarii belongs to a class of double stars called symbiotic stars. The primary star is an aging red giant and its companion is a compact burned-out star known as a white dwarf. The red giant primary star is classified as a Mira variable that is over 400 times larger than our Sun. The bloated monster star pulsates, changes temperature, and varies in brightness by a factor of 750 times over a roughly 390-day period. At its peak the star is blinding at nearly 5,000 times our Sun’s brightness. When the white dwarf swings closest to the red giant along its 44-year orbital period, it gravitationally siphons off hydrogen gas. This material accumulates in the accretion disk surrounding the white dwarf, until it undergoes a powerful outburst and jet ejection, especially during the closest approach of the white dwarf to the red giant donor star.
These events have more than just a passing interest to astronomers and laymen alike in that this is one known way — as well as the truly titanic but extremely rare supernova events — to release chemical elements heavier than hydrogen and helium into the interstellar medium. Heavier elements like carbon, nitrogen, and oxygen are critical building blocks of planets like the Earth and lifeforms such as our own. They are formed in the deep interiors of stars, where the temperature is high enough to fuse hydrogen and helium.
This outburst ejects powerful jets seen as filaments shooting out from the binary system, forming loops and trails as the plasma emerges in streamers. The plasma is twisted by the force of the explosion and channeled upwards and outwards by strong magnetic fields. The outflow appears to bend back on itself into a spiral pattern. The filaments are glowing in visible light because they are energized by blistering radiation from the stellar duo that is R Aquarii. The nebula around the binary star is known as Cederblad 211, and may be the remnant of a past nova.
The scale of the event is extraordinary even in astronomical terms since emitting material can be traced out to at least 400 billion kilometres — or 2,500 times the distance between the Sun and the Earth — from the central core.
The ESA/Hubble team has developed a unique timelapse of the object consisting of multiple observing programmes that span from 2014 to 2023. Across the five images, the rapid and dramatic evolution of the binary star and its surrounding nebula can be seen. The binary star dims and brightens, seen by the size of the red diffraction spikes around it, due to the strong pulsations of the red giant star. The nebula is shown in mostly green colours, but bluer parts of it come in and out of view: this is because they are being illuminated as the lighthouse-like beam of light from the spinning binary star sweeps over them.
This image features R Aquarii, a symbiotic binary star that lies only roughly 1,000 light-years from Earth in the constellation Aquarius. This is a type of binary star system consisting of a white dwarf and a red giant that is surrounded by a large, dynamic nebula. Credit: NASA, ESA, M. Stute, M. Karovska, D. de Martin & M. Zamani (ESA/Hubble)
Hubble’s new observations of Jupiter’s Great Red Spot, collected over 90 days between December 2023 to March 2024
Astronomers have observed Jupiter’s legendary Great Red Spot (GRS), an anticyclone large enough to swallow Earth, for at least 150 years. But there are always new surprises – especially when the NASA/ESA Hubble Space Telescope takes a close-up look at it.
Using Hubble Space Telescope data spanning approximately 90 days (between December 2023 and March 2024) when the giant planet Jupiter was approximately 740 million kilometres from the Sun, astronomers measured the Great Red Spot’s size, shape, brightness, colour, and vorticity over one full oscillation cycle. The data reveal that the Great Red Spot is not as stable as it might look. It was observed going through an oscillation in its elliptical shape, jiggling like a bowl of gelatin. The cause of the 90-day oscillation is unknown. Credit: NASA, ESA, A. Simon (GSFC)
Hubble’s new observations of the famous red storm, collected over 90 days between December 2023 to March 2024, reveal that the GRS is not as stable as it might look. The recent data show the GRS jiggling like a bowl of gelatin. The combined Hubble images allowed astronomers to assemble a time-lapse movie of the squiggly behaviour of the GRS.
“While we knew its motion varies slightly in its longitude, we didn’t expect to see the size oscillate. As far as we know, it’s not been identified before,” said Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This is really the first time we’ve had the proper imaging cadence of the GRS. With Hubble’s high resolution we can say that the GRS is definitively squeezing in and out at the same time as it moves faster and slower. That was very unexpected, and at present there are no hydrodynamic explanations.”
Hubble monitors Jupiter and the other outer solar system planets every year through the Outer Planet Atmospheres Legacy program (OPAL) led by Simon, but these observations were from a program dedicated to the GRS. Understanding the mechanisms of the largest storms in the solar system puts the theory of hurricanes on Earth into a broader cosmic context, which might be applied to better understanding the meteorology on planets around other stars.
Using Hubble Space Telescope data spanning approximately 90 days (between December 2023 and March 2024) when the giant planet Jupiter was approximately 740 million kilometres from the Sun, astronomers measured the Great Red Spot’s size, shape, brightness, colour, and vorticity over a full oscillation cycle. The data reveal that the Great Red Spot is not as stable as it might look. It was observed going through an oscillation in its elliptical shape, jiggling like a bowl of gelatin. The cause of the 90-day oscillation is unknown. The observation is part of the Outer Planet Atmospheres Legacy program (OPAL). Credit: NASA, ESA, A. Simon (GSFC)
Simon’s team used Hubble to zoom in on the GRS for a detailed look at its size, shape, and any subtle colour changes.
“When we look closely, we see a lot of things are changing from day to day,” said Simon.
This includes ultraviolet-light observations showing that the distinct core of the storm gets brightest when the GRS is at its largest size in its oscillation cycle. This indicates less haze absorption in the upper atmosphere.
“As it accelerates and decelerates, the GRS is pushing against the windy jet streams to the north and south of it,” said co-investigator Mike Wong of the University of California at Berkeley. “It’s similar to a sandwich where the slices of bread are forced to bulge out when there’s too much filling in the middle.”
Wong contrasted this to Neptune, where dark spots can drift wildly in latitude without strong jet streams to hold them in place. Jupiter’s Great Red Spot has been held at a southern latitude, trapped between the jet streams, for the extent of Earth-bound telescopic observations.
The team has continued watching the GRS shrink since the OPAL program began 10 years ago. They predict it will keep shrinking before taking on a stable, less-elongated, shape.
“Right now it’s over-filling its latitude band relative to the wind field. Once it shrinks inside that band the winds will really be holding it in place,” said Simon.
The team predicts that the GRS will probably stabilise in size, but for now Hubble only observed it for one oscillation cycle.
“This is a great example of the power of Hubble’s exquisite imaging for monitoring of the atmospheres of the outer planets,” said co-investigator Patrick Irwin of the University of Oxford. “With these new observations we were able to study the dynamics and evolution of the GRS over three months, building on our understanding of the long-term properties of Jupiter obtained from the OPAL program over the past decade.”
The researchers hope that in the future other high-resolution images from Hubble might identify other Jovian parameters that indicate the underlying cause of the oscillation.
Galaxy GS-NDG-9422 (9422): Webb finds potential missing link to first stars
Looking deep into the early universe with the NASA/ESA/CSA James Webb Space Telescope, astronomers have found something unprecedented: a galaxy with an odd light signature, which they attribute to its gas outshining its stars.
The galaxy GS-NDG-9422 may easily have gone unnoticed. However, what appears as a faint blur in this James Webb Space Telescope image may actually be a groundbreaking discovery that points astronomers on a new path of understanding galaxy evolution in the early universe. Detailed information on the galaxy’s chemical makeup, captured by Webb’s NIRSpec (Near-Infrared Spectrograph) instrument, indicates that the light we see in this image is coming from the galaxy’s hot gas, rather than its stars. That is the best explanation astronomers have discovered so far to explain the unexpected features in the light spectrum. They think that the galaxy’s stars are so extremely hot and massive that they are heating up the nebular gas in the galaxy to more than 80,000 degrees Celsius, allowing it to shine even brighter in near-infrared light than the stars themselves. The authors of a new study on Webb’s observations of the galaxy think GS-NDG-9422 may represent a never-before-seen phase of galaxy evolution in the early universe, within the first billion years after the big bang. Their task now is to see if they can find more galaxies displaying the same features. Credit: NASA, ESA, CSA, STScI, A. Cameron (University of Oxford)
Found approximately one billion years after the big bang, galaxy GS-NDG-9422 (9422) may be a missing-link phase of galactic evolution between the universe’s first stars and familiar, well-established galaxies.
“My first thought in looking at the galaxy’s spectrum was, ‘that’s weird,’ which is exactly what the Webb telescope was designed to reveal: totally new phenomena in the early universe that will help us understand how the cosmic story began,” said lead researcher Alex Cameron of the University of Oxford in the United Kingdom.
Cameron reached out to colleague Harley Katz, a theorist, to discuss the strange data. Working together, their team found that computer models of cosmic gas clouds heated by very hot, massive stars, to an extent that the gas shone brighter than the stars, was nearly a perfect match to Webb’s observations.
“It looks like these stars must be much hotter and more massive than what we see in the local universe, which makes sense because the early universe was a very different environment,” said Katz, of Oxford and the University of Chicago, U.S.A.
In the local universe, typical hot, massive stars have a temperature ranging between 40,000 to 50,000 degrees Celsius. According to the team, galaxy 9422 has stars hotter than 80,000 degrees Celsius.
The research team suspects that the galaxy is in the midst of a brief phase of intense star formation inside a cloud of dense gas that is producing a large number of massive, hot stars. The gas cloud is being hit with so many photons of light from the stars that it is shining extremely brightly.
In addition to its novelty, nebular gas outshining stars is intriguing because it is something predicted in the environments of the universe’s first generation of stars, which astronomers classify as Population III stars.
“We know that this galaxy does not have Population III stars, because the Webb data shows too much chemical complexity. However, its stars are different from what we are familiar with – the exotic stars in this galaxy could be a guide for understanding how galaxies transitioned from primordial stars to the types of galaxies we already know,” said Katz.
At this point, galaxy 9422 is one example of this phase of galaxy development, so there are still many questions to be answered. Are these conditions common in galaxies at this time period, or a rare occurrence? What more can they tell us about even earlier phases of galaxy evolution? Cameron, Katz, and their research colleagues are actively identifying more galaxies to add to this population to better understand what was happening in the universe within the first billion years after the big bang.
“It’s a very exciting time, to be able to use the Webb telescope to explore this time in the universe that was once inaccessible,” Cameron said. “We are just at the beginning of new discoveries and understanding.”
The galaxy GS-NDG-9422 may easily have gone unnoticed. However, what appears as a faint blur in this James Webb Space Telescope image may actually be a groundbreaking discovery that points astronomers on a new path of understanding galaxy evolution in the early universe. Detailed information on the galaxy’s chemical makeup, captured by Webb’s NIRSpec (Near-Infrared Spectrograph) instrument, indicates that the light we see in this image is coming from the galaxy’s hot gas, rather than its stars. That is the best explanation astronomers have discovered so far to explain the unexpected features in the light spectrum. They think that the galaxy’s stars are so extremely hot and massive that they are heating up the nebular gas in the galaxy to more than 80,000 degrees Celsius, allowing it to shine even brighter in near-infrared light than the stars themselves. The authors of a new study on Webb’s observations of the galaxy think GS-NDG-9422 may represent a never-before-seen phase of galaxy evolution in the early universe, within the first billion years after the big bang. Their task now is to see if they can find more galaxies displaying the same features. Credit: NASA, ESA, CSA, STScI, A. Cameron (University of Oxford)
Webb provides another look into galactic collisions at Arp 107
An interaction between an elliptical galaxy and a larger spiral galaxy, collectively known as Arp 107, seems to have given the spiral a happier outlook thanks to the two bright ‘eyes’ and the wide semicircular ‘smile’ that have resulted. This image is a composite, combining observations from Webb’s MIRI (Mid-InfraRed Instrument) and NIRCam (Near-InfraRed Camera).
NIRCam highlights the stars within both galaxies and reveals the connection between them: a transparent, white bridge of stars pulled from both galaxies during their passage. MIRI data, represented in orange-red, show star-forming regions and dust that is composed of soot-like organic molecules known as polycyclic aromatic hydrocarbons. MIRI also provides a snapshot of the bright nucleus of the large spiral, home to a supermassive black hole.
This image of Arp 107, obtained by Webb’s MIRI (Mid-InfraRed Instrument), reveals the supermassive black hole that lies in the centre of the large spiral galaxy to the right, as evidenced by the small, bright central ‘core’. This bright core, where the black hole is pulling much of the dust into lanes, also features Webb’s characteristic diffraction spikes, caused by the light that it emits interacting with the structure of the telescope itself. Perhaps the defining feature of the region, which MIRI reveals, are the millions of young stars that are forming, highlighted in blue. These stars are surrounded by dusty silicates and soot-like molecules known as polycyclic aromatic hydrocarbons. The small elliptical galaxy to the left, which has already completed much of its star formation, is composed of many of these organic molecules. Credit: NASA, ESA, CSA, STScI
The spiral galaxy is classified as a Seyfert galaxy, one of the two largest groups of active galaxies, along with galaxies that host quasars. Seyfert galaxies aren’t as luminous or as distant as quasars, so they are better places to study similar phenomena in lower-energy light, like infrared.
This region is much like the Cartwheel Galaxy, one of the first interacting galaxies that Webb observed. Arp 107 may have turned out very similar in appearance to the Cartwheel, but since the smaller elliptical galaxy had an off-centre collision instead of a direct hit, the spiral galaxy got away with only its spiral arms being disturbed.
This composite image of Arp 107, created with data from the James Webb Space Telescope’s NIRCam (Near-InfraRed Camera) and MIRI (Mid-InfraRed Instrument), reveals a wealth of information about the star formation taking place in these two galaxies and how they collided hundreds of million years ago. The near-infrared data, shown in white, show older stars, which shine brightly in both galaxies, as well as the tenuous gas bridge that runs between them. The vibrant background galaxies are also brightly illuminated at these wavelengths. On the other hand, MIRI data show the young stars and star-forming regions in vibrant orange and red. Our view in the mid-infrared provides the best view of the collision point, given the noticeable gap at the top of the spiral galaxy. This collision not only began a new bout of star formation in the region, but also produced an endearing smile. Credit: NASA, ESA, CSA, STScI
The collision isn’t as bad as it sounds. Although there was much star formation occurring before, collisions between galaxies can compress gas, improving the conditions needed for more stars to form. On the other hand, as Webb reveals, collisions also disperse a lot of gas, potentially depriving new stars of the material they need to form.
Webb has captured these galaxies in the process of merging, which will take hundreds of millions of years. As the two galaxies rebuild after the chaos of their collision, Arp 107 may lose its smile, but it will inevitably turn into something just as interesting for future astronomers to study.
Arp 107 is located 465 million light-years from Earth in the constellation Leo Minor.
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 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 75 000 years for light to travel a distance equal to the length of the bar.) One light-year is equal to about 5.88 trillion miles or 9.46 trillion kilometres. The field of view shown in this image is approximately 450 000 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 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. Credit: NASA, ESA, CSA, STScI
Hubble finds more black holes than expected in the early Universe
With the help of the NASA/ESA Hubble Space Telescope, an international team of researchers led by scientists in the Department of Astronomy at Stockholm University has found more black holes in the early Universe than has previously been reported. The new result can help scientists understand how supermassive black holes were created.
This is a new image of the Hubble Ultra Deep Field. The first deep imaging of the field was done with Hubble in 2004. The same survey field was observed again by Hubble several years later, and was then reimaged in 2023. By comparing Hubble Wide Field Camera 3 near-infrared exposures taken in 2009, 2012, and 2023, astronomers found evidence for flickering supermassive black holes in the hearts of early galaxies. One example is seen as a bright object in the inset. Some supermassive black holes do not swallow surrounding material constantly, but in fits and bursts, making their brightness flicker. This can be detected by comparing Hubble Ultra Deep Field frames taken at different epochs. The survey found more black holes than predicted. The image was created from Hubble data from the following proposals: 9978, 10086 (S. Beckwith); 11563 (G. Illingworth); 12498 (R. Ellis); and 17073 (M. Hayes). These images are composites of separate exposures acquired by the ACS and WFC3 instruments on the Hubble Space Telescope. Credit: NASA, ESA, M. Hayes (Stockholm University), J. DePasquale (STScI)
Scientists do not currently have a complete picture of how the first black holes formed, not long after the Big Bang. It is known that supermassive black holes, that can weigh more than a billion suns, exist at the centre of several galaxies less than a billion years after the Big Bang.
“Many of these objects seem to be more massive than we originally thought they could be at such early times — either they formed very massive or they grew extremely quickly,” said Alice Young, a PhD student from Stockholm University and co-author of the study published in The Astrophysical Journal Letters.
Black holes play an important role in the lifecycle of all galaxies, but there are major uncertainties in our understanding of how galaxies evolve. In order to gain a complete picture of the link between galaxy and black hole evolution, the researchers used Hubble to survey how many black holes exist among a population of faint galaxies when the Universe was just a few percent of its current age.
Initial observations of the survey region were re-photographed by Hubble several years later. This allowed the team to measure variations in the brightness of the galaxies. These variations are a tell-tale sign of black holes. The team identified more black holes than previously found by other methods.
The new observational results suggest that some black holes likely formed by the collapse of massive, pristine stars during the first billion years of cosmic time. These types of stars can only exist at very early times in the Universe, because later generations of stars are polluted by the remnants of stars that have already lived and died. Other alternatives for black hole formation include collapsing gas clouds, mergers of stars in massive clusters, and ‘primordial’ black holes that formed (by physically speculative mechanisms) in the first few seconds after the Big Bang. With this new information about black hole formation, more accurate models of galaxy formation can be constructed.
“The formation mechanism of early black holes is an important part of the puzzle of galaxy evolution,” said Matthew Hayes from the Department of Astronomy at Stockholm University and lead author of the study. “Together with models for how black holes grow, galaxy evolution calculations can now be placed on a more physically motivated footing, with an accurate scheme for how black holes came into existence from collapsing massive stars.”
Astronomers are also making observations with the NASA/ESA/CSA James Webb Space Telescope to search for galactic black holes that formed soon after the Big Bang, to understand how massive they were and where they were located.
This is an image of the Hubble Ultra Deep Field, taken in 2004. By comparing exposures taken in later years, astronomers found evidence for flickering supermassive black holes in the hearts of early galaxies. One example is seen as a bright object in the inset. Some supermassive black holes do not swallow surrounding material constantly, but in fits and starts, making their brightness flicker. This can be detected by comparing Hubble Ultra Deep Field frames taken at different epochs. The survey found more black holes than predicted. The image was created from Hubble data from the following proposals: 9978, 10086 (S. Beckwith); 11563 (G. Illingworth); 12498 (R. Ellis); and 17073 (M. Hayes). These images are composites of separate exposures acquired by the ACS and WFC3 instruments on the Hubble Space Telescope. Credit: NASA, ESA, M. Hayes (Stockholm University), J. DePasquale (STScI)
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.
