Astronomy

Hubble hunts for intermediate-sized black hole close to home

By ScientifiCult 23 May 2023

Hubble hunts for intermediate-sized black hole close to home; the study has been published in the Monthly Notices of the Royal Astronomical Society

Astronomers using the NASA/ESA Hubble Space Telescope have come up with what they say is some of their best evidence yet for the presence of a rare class of intermediate-sized black holes, having found a strong candidate lurking at the heart of the closest globular star cluster to Earth, located 6000 light-years away.

Messier 4 M4 — Hubble hunts for intermediate-sized black hole close to home. A Hubble Space Telescope image of the globular star cluster, Messier 4. The cluster is a dense collection of several hundred thousand stars. Astronomers suspect that an intermediate-mass black hole, weighing as much as 800 times the mass of our Sun, is lurking, unseen, at its core. Credit: ESA/Hubble & NASA

Like intense gravitational potholes in the fabric of space, virtually all black holes seem to come in two sizes: small and humongous. It’s estimated that our galaxy is littered with 100 million small black holes (several times the mass of our Sun) created from exploded stars. The universe at large is flooded with supermassive black holes, weighing millions or billions of times our Sun’s mass and found in the centres of galaxies.

A long-sought missing link is an intermediate-mass black hole, weighing roughly 100 to 100,000 times our Sun’s mass. How would they form, where would they hang out, and why do they seem to be so rare?

Astronomers have identified other possible intermediate-mass black holes using a variety of observational techniques. Two of the best candidates — 3XMM J215022.4-055108, which Hubble helped discover in 2020, and HLX-1, identified in 2009 — reside in the outskirts of other galaxies. Each of these possible black holes has the mass of tens of thousands of suns, and may have once been at the centres of dwarf galaxies.

Looking much closer to home, there have been a number of suspected intermediate-mass black holes detected in dense globular star clusters orbiting our Milky Way galaxy. For example, in 2008, Hubble astronomers announced the suspected presence of an intermediate-mass black hole in the globular cluster Omega Centauri. For a number of reasons, including the need for more data, these and other intermediate-mass black hole findings still remain inconclusive and do not rule out alternative theories.

Hubble’s unique capabilities have now been used to zero-in on the core of the globular star cluster Messier 4 (M4) to go black-hole hunting with higher precision than in previous searches.

“You can’t do this kind of science without Hubble,”

said Eduardo Vitral of the Space Telescope Science Institute in Baltimore, Maryland, and formerly of the Institut d’Astrophysique de Paris (IAP, Sorbonne University) in Paris, France, lead author on a paper to be published in the Monthly Notices of the Royal Astronomical Society.

Vitral’s team has detected a possible intermediate-mass black hole of roughly 800 solar masses. The suspected object can’t be seen, but its mass is calculated by studying the motion of stars caught in its gravitational field, like bees swarming around a hive. Measuring their motion takes time, and a lot of precision. This is where Hubble accomplishes what no other present-day telescope can do. Astronomers looked at 12 years’ worth of M4 observations from Hubble, and resolved pinpoint stars.

ESA’s Gaia spacecraft also contributed to this result with scans of over 6000 stars that constrained the global shape of the cluster and its mass. Hubble’s data tend to rule out alternative theories for this object, such as a compact central cluster of unresolved stellar remnants like neutron stars, or smaller black holes swirling around each other.

“Using the latest Gaia and Hubble data, it was not possible to distinguish between a dark population of stellar remnants and a single larger point-like source,” says Vitral. “So one of the possible theories is that rather than being lots of separate small dark objects, this dark mass could be one medium-sized black hole.”

“We have good confidence that we have a very tiny region with a lot of concentrated mass. It’s about three times smaller than the densest dark mass that we had found before in other globular clusters,” he continued. “The region is more compact than what we can reproduce with numerical simulations when we take into account a collection of black holes, neutron stars, and white dwarfs segregated at the cluster’s centre. They are not able to form such a compact concentration of mass.”

A grouping of close-knit objects would be dynamically unstable. If the object isn’t a single intermediate-mass black hole, it would require an estimated 40 smaller black holes crammed into a space only one-tenth of a light-year across to produce the observed stellar motions. The consequences are that they would merge and/or be ejected in a game of interstellar pinball.

“We measure the motions of stars and their positions, and we apply physical models that try to reproduce these motions. We end up with a measurement of a dark mass extension in the cluster’s centre,” said Vitral. “The closer to the central mass, the more randomly the stars are moving. And, the greater the central mass, the faster these stellar velocities.”

Because intermediate-mass black holes in globular clusters have been so elusive, Vitral cautions, “While we cannot completely affirm that it is a central point of gravity, we can show that it is very small. It’s too tiny for us to be able to explain other than it being a single black hole. Alternatively, there might be a stellar mechanism we simply don’t know about, at least within current physics.”

“Science is rarely about discovering something new in a single moment. It’s about becoming more certain of a conclusion step by step, and this could be one step towards being sure that intermediate-mass black holes exist,” explains Gaia mission scientist Timo Prusti. “Data from Gaia Data Release 3 on the proper motion of stars in the Milky Way were essential in this study. Future Gaia Data Releases, as well as follow-up studies from the Hubble and James Webb Space Telescopes could shed further light.”

Press release from ESA Hubble

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Webb finds water in Comet 238P/Read, a rare main belt comet

By ScientifiCult 15 May 2023

Webb finds water, and a new mystery, in Comet 238P/Read, a rare main belt comet

The NASA/ESA/CSA James Webb Space Telescope has enabled another long-sought scientific breakthrough, this time for Solar System scientists studying the origins of the water that has made life on Earth possible. Using Webb’s NIRSpec (Near-Infrared Spectrograph) instrument, astronomers have confirmed gas – specifically water vapour – around a comet in the main asteroid belt for the first time, proving that water from the primordial Solar System can be preserved as ice in that region. However, the successful detection of water comes with a new puzzle: unlike other comets, Comet 238P/Read had no detectable carbon dioxide.

water Comet 238 P/Read — This artist’s concept of Comet 238P/Read shows the main belt comet sublimating—its water ice vapourising as its orbit approaches the Sun. This is significant, as the sublimation is what distinguishes comets from asteroids, creating their distinctive tail and hazy halo, or coma. The NASA/ESA/CSA James Webb Space Telescope’s detection of water vapour at Comet Read is a major benchmark in the study of main belt comets, and in the broader investigation of the origin of Earth’s abundant water.
Credit: NASA, ESA

“Our water-soaked world, teeming with life and unique in the universe as far as we know, is something of a mystery – we’re not sure how all this water got here,” said Stefanie Milam, Webb Deputy Project Scientist for Planetary Science and a co-author on the study reporting the finding. “Understanding the history of water distribution in the Solar System will help us to understand other planetary systems, and if they could be on their way to hosting an Earth-like planet,” she added.

Comet Read is a main belt comet – an object that resides in the main asteroid belt but which periodically displays a halo, or coma, and tail like a comet. Main belt comets themselves are a fairly new classification, and Comet Read was one of the original three comets used to establish the category. Before that, comets were understood to originate in the Kuiper Belt and Oort Cloud, beyond the orbit of Neptune, where their ices could be preserved farther from the Sun. Frozen material that vaporises as they approach the Sun is what gives comets their distinctive coma and streaming tail, differentiating them from asteroids. Scientists have long speculated that water ice could be preserved in the warmer asteroid belt, inside the orbit of Jupiter, but definitive proof was elusive – until Webb.

“In the past we’ve seen objects in the main belt with all the characteristics of comets, but only with this precise spectral data from Webb can we say yes, it’s definitely water ice that is creating that effect,” explained astronomer Michael Kelley of the University of Maryland, lead author of the study.

“With Webb’s observations of Comet Read, we can now demonstrate that water ice from the early Solar System can be preserved in the asteroid belt,” Kelley said.

This image of Comet 238P/Read was captured by the NIRCam (Near-Infrared Camera) instrument on the NASA/ESA/CSA James Webb Space Telescope on 8 September 2022. It displays the hazy halo, called the coma, and tail that are characteristic of comets, as opposed to asteroids. The dusty coma and tail result from the vapourisation of ices as the Sun warms the main body of the comet. Credit: NASA, ESA, CSA, M. Kelley (University of Maryland), H. Hsieh (Planetary Science Institute), A. Pagan (STScI)

The missing carbon dioxide was a bigger surprise. Typically carbon dioxide makes up about 10 percent of the volatile material in a comet that can be easily vaporised by the Sun’s heat. The science team presents two possible explanations for the lack of carbon dioxide. One possibility is that Comet Read did have carbon dioxide when it formed, but has lost that because of warm temperatures.

“Being in the asteroid belt for a long time could do it – carbon dioxide vaporises more easily than water ice, and could percolate out over billions of years,” Kelley said. Alternatively, he said, Comet Read may have formed in a particularly warm pocket of the Solar System, where no carbon dioxide was available.

The next step is taking the research beyond Comet Read to see how other main belt comets compare, says astronomer Heidi Hammel of the Association of Universities for Research in Astronomy (AURA), lead for Webb’s Guaranteed Time Observations for Solar System objects and co-author of the study.

“These objects in the asteroid belt are small and faint, and with Webb we can finally see what is going on with them and draw some conclusions. Do other main belt comets also lack carbon dioxide? Either way it will be exciting to find out,” Hammel said.

Co-author Milam imagines the possibilities of bringing the research even closer to home. “Now that Webb has confirmed there is water preserved as close as the asteroid belt, it would be fascinating to follow up on this discovery with a sample collection mission, and learn what else the main belt comets can tell us.”

The study is published in the journal Nature.

Press release from ESA Webb.

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Webb looks for Fomalhaut’s asteroid belt and finds much more

By ScientifiCult 8 May 2023

Webb looks for Fomalhaut’s asteroid belt and finds much more

Astronomers used the NASA/ESA/CSA James Webb Space Telescope to image the warm dust around a nearby young star, Fomalhaut, in order to study the first asteroid belt ever seen outside of our Solar System in infrared light. But to their surprise, they found that the dusty structures are much more complex than the asteroid and Kuiper dust belts of our Solar System. Overall, there are three nested belts extending out to 23 billion kilometres from the star — that’s 150 times the distance of Earth from the Sun. The scale of the outermost belt is roughly twice the scale of our Solar System’s Kuiper Belt of small bodies and cold dust beyond Neptune. The inner belts — which had never been seen before — were revealed by Webb for the first time.

Webb Fomalhaut’s asteroid beltThe NASA/ESA Hubble Space Telescope and ESA's Herschel Space Observatory, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), have previously taken sharp images of the outermost belt. However, none of them found any structure interior to it.

[Image description: An orange oval extends from the 1 o’clock to 7 o’clock positions. It features a prominent outer ring, a darker gap, an intermediate ring, a narrower dark gap, and a bright inner disc. At the centre is a ragged black spot indicating a lack of data.]

Credit:
NASA, ESA, CSA, A. Pagan (STScI), A. Gáspár (University of Arizona) — Webb looks for Fomalhaut’s asteroid belt and finds much more. This image of the dusty debris disc surrounding the young star Fomalhaut is from Webb’s Mid-Infrared Instrument (MIRI). It reveals three nested belts extending out to 23 billion kilometres from the star. The inner belts — which had never been seen before — were revealed by Webb for the first time.
The NASA/ESA Hubble Space Telescope and ESA’s Herschel Space Observatory, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), have previously taken sharp images of the outermost belt. However, none of them found any structure interior to it.
These belts are most likely shaped by the gravitational forces produced by unseen planets. Credit: NASA, ESA, CSA, A. Pagan (STScI), A. Gáspár (University of Arizona)

The belts encircle the young hot star, which can be seen with the naked eye as the brightest star in the southern constellation Piscis Austrinus. The dusty belts are the debris from collisions of larger bodies, analogous to asteroids and comets, and are frequently described as ‘debris discs’.

“I would describe Fomalhaut as the archetype of debris discs found elsewhere in our galaxy, because it has components similar to those we have in our own planetary system,” said András Gáspár of the University of Arizona in Tucson and lead author of a new paper describing these results. “By looking at the patterns in these rings, we can actually start to make a little sketch of what a planetary system ought to look like — if we could actually take a deep enough picture to see the suspected planets.”

The NASA/ESA Hubble Space Telescope and ESA’s Herschel Space Observatory, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), have previously taken sharp images of the outermost belt. However, none of them found any structure interior to it. The inner belts have been resolved for the first time by Webb in infrared light.

“Where Webb really excels is that we’re able to physically resolve the thermal glow from dust in those inner regions. So you can see inner belts that we could never see before,” said Schuyler Wolff, another member of the team at the University of Arizona.

Hubble, ALMA, and Webb are tag-teaming to assemble a holistic view of the debris discs around a number of stars. “With Hubble and ALMA, we were able to image a bunch of Kuiper Belt analogues, and we’ve learned loads about how outer discs form and evolve,” said Wolff. “But we need Webb to allow us to image a dozen or so asteroid belts elsewhere. We can learn just as much about the inner warm regions of these discs as Hubble and ALMA taught us about the colder outer regions.”

These belts are most likely shaped by the gravitational forces produced by unseen planets. Similarly, inside our Solar System Jupiter corrals the asteroid belt, the inner edge of the Kuiper Belt is sculpted by Neptune, and the outer edge could be shepherded by as-yet-unseen bodies beyond it. As Webb images more systems, we will learn about the configurations of their planets.

Webb looks for Fomalhaut’s asteroid belt and finds much more. This image of the Fomalhaut system, captured by Webb’s Mid-Infrared Instrument (MIRI), shows compass arrows, scale bar, and colour key for reference. Labels indicate the various structures. At right, a great dust cloud is highlighted and pullouts show it in two infrared wavelengths: 23 and 25.5 microns.
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 astronomical units, which is the average distance between Earth and the Sun: 150 million kilometres. The outer ring is about 240 astronomical units in diameter.
This image shows invisible mid-infrared wavelengths of light that have been translated into visible-light colours. The colour key and labels show which MIRI filters were used when collecting the light.
Credit: NASA, ESA, CSA, A. Pagan (STScI), A. Gáspár (University of Arizona)

Fomalhaut’s dust ring was discovered in 1983 in observations made by NASA’s Infrared Astronomical Satellite (IRAS). The existence of the ring has also been inferred from previous and longer-wavelength observations using submillimetre telescopes on Maunakea, Hawai‘i, NASA’s Spitzer Space Telescope, and Caltech’s Submillimeter Observatory.

“The belts around Fomalhaut are kind of a mystery novel: Where are the planets?” said George Rieke, another team member and US science lead for Webb’s Mid-Infrared Instrument (MIRI), which made these observations. “I think it’s not a very big leap to say there’s probably a really interesting planetary system around the star.”

“We definitely didn’t expect the more complex structure with the second intermediate belt and then the broader asteroid belt,” added Wolff. “That structure is very exciting because any time an astronomer sees a gap and rings in a disc, they say, ‘There could be an embedded planet shaping the rings!’”

Webb also imaged what Gáspár dubs ‘the great dust cloud’, which may be evidence for a collision occurring in the outer ring between two protoplanetary bodies. This is a different feature from the suspected planet first seen inside the outer ring by Hubble in 2008. Subsequent Hubble observations showed that by 2014 the object had vanished. A plausible interpretation is that this newly discovered feature, like the earlier one, is an expanding cloud of very fine dust particles from two icy bodies that smashed into each other.

The idea of a protoplanetary disc around a star goes back to the late 1700s when astronomers Immanuel Kant and Pierre-Simon Laplace independently developed the theory that the Sun and planets formed from a rotating gas cloud that collapsed and flattened under gravity. Debris discs develop later, following the formation of planets and dispersal of the primordial gas in the systems. They show that small bodies like asteroids are colliding catastrophically and pulverising their surfaces into huge clouds of dust and other debris. Observations of dust provide unique clues to the structure of an exoplanetary system, reaching down to Earth-sized planets and even asteroids, which are much too small to see individually.

“This very exciting result highlights the unique power of MIRI to study the structures carved by planets in the innermost regions of circumstellar discs,“ adds Gillian Wright, European principal investigator for MIRI and Director of the UK Astronomy Technology Centre (UKATC).

The team’s results are being published in the journal Nature Astronomy.

Press release from ESA Webb.

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Shadow playing with the red dwarf star TW Hydrae

By ScientifiCult 4 May 2023

Hubble follows shadow play around planet-forming disc: the young star TW Hydrae is playing ‘shadow puppets’ with scientists

In 2017 astronomers reported discovering a shadow sweeping across the face of a vast pancake-shaped disc of gas and dust surrounding the red dwarf star TW Hydrae. The shadow isn’t from a planet, but from an inner disc slightly inclined relative to the much larger outer disc — causing it to cast a shadow. One explanation is that an unseen planet’s gravity is pulling dust and gas into its inclined orbit. Now, a second shadow — playing a game of peek-a-boo — has emerged in just a few years between observations stored in the MAST archive of the NASA/ESA Hubble Space Telescope. This could be from yet another disc nestled inside the system. The two discs are likely evidence of a pair of planets under construction.

Hubble images TW Hydrae Disc Shadows (annotated). Comparison images from the NASA/ESA Hubble Space Telescope, taken several years apart, have uncovered two eerie shadows moving counterclockwise across a disc of gas and dust encircling the young star TW Hydrae. The discs are tilted face-on as seen from Earth and so give astronomers a bird’s-eye view of what’s happening around the star. The left image, taken in 2016, shows just one shadow [A] at the 11 o’clock position. This shadow is cast by an inner disc that is slightly inclined to the outer disc and so blocks starlight. The picture on the left shows a second shadow that emerged from yet another nested disc at the 7 o’clock position, as photographed in 2021. What was originally the inner disc is marked [B] in this later view. The shadows rotate around the star at different rates like the hand on a clock. They are evidence for two unseen planets that have pulled dust into their orbits. This makes them slightly inclined to each other. This is a visible-light photo taken with the Space Telescope Imaging Spectrograph. Artificial colour has been added to enhance details.
Credit: NASA, ESA, J. Debes STScI

TW Hydrae is less than 10 million years old and resides about 200 light-years away. In its infancy, some 4.6 billion years ago, our Solar System may have resembled the TW Hydrae system. Because the TW Hydrae system is tilted nearly face-on as seen from Earth, it is an optimum target for getting a bird’s-eye view of a planetary construction yard.

The second shadow was discovered in observations obtained on 6 June 2021, as part of a multi-year programme designed to track the shadows in circumstellar discs. John Debes of AURA/STScI for the European Space Agency at the Space Telescope Science Institute in Baltimore, Maryland, compared these latest observations of the TW Hydrae disc to Hubble observations made several years ago.

“We found out that the shadow had done something completely different,” said Debes, who is principal investigator and lead author of the study published in The Astrophysical Journal. “When I first looked at the data, I thought something had gone wrong with the observation because it wasn’t what I was expecting. I was flummoxed at first, and all my collaborators were like: what is going on? We really had to scratch our heads and it took us a while to actually figure out an explanation.”

“We hatched a theory of what might be causing the changing shadows,” added Rebecca Nealon, a member of the science team at the University of Warwick in the United Kingdom. “But to test this we had to run sophisticated models where we varied the number of discs and their orientations to try to reproduce Hubble’s observations.”

shadow TW Hydrae — Concentric gas and dust discs around the star TW Hydrae. This illustration is based on NASA/ESA Hubble Space Telescope images of a gas and dust discs encircling the young star TW Hydrae. Hubble photos show shadows sweeping across the discs encircling the system. The interpretation is that these shadows are from slightly inclined inner discs that block starlight from reaching the outer disc, and therefore cast a shadow. The discs are slightly inclined to each other because of the gravitational pull of unseen planets warping the disc structure. Credit: NASA. ESA, L. Hustak (STScI)

The best solution the team came up with is that there are two misaligned discs casting shadows. They were so close to each other in the earlier observation they were missed. Over time they’ve now separated and split into two shadows.

“We’ve never really seen this before on a protoplanetary disc. It makes the system much more complex than we originally thought,” said Debes.

The simplest explanation is that the misaligned discs are likely caused by the gravitational pull of two planets in slightly different orbital planes. Hubble is piecing together a holistic view of the architecture of the system.

The discs may be proxies for planets that are lapping each other as they whirl around the star. It’s sort of like spinning two vinyl records at slightly different speeds. Sometimes the labels will match up but then one gets ahead of the other.

“It does suggest that the two planets have to be fairly close to each other. If one was moving much faster than the other, this would have been noticed in earlier observations. It’s like two racing cars that are close to each other, but one slowly overtakes and laps the other,” said Debes.

The suspected planets are located in a region roughly the distance of Jupiter from our Sun. And the shadows complete one rotation around the star about every 15 years — the orbital period that would be expected at that distance from the star.

Also, these two inner discs are inclined by about five to seven degrees relative to the plane of the outer disc. This is comparable to the range of orbital inclinations inside our Solar System.

“This is right in line with typical Solar System-style architecture,” said Debes.

The outer disc that the shadows are falling on may extend as far as several times the radius of our Solar System’s Kuiper belt. This larger disc has a curious gap at twice Pluto’s average distance from the Sun. This might be evidence for a third planet in the system.

Any inner planets would be difficult to detect because their light would be lost in the glare of the star. Also, dust in the system would dim their reflected light. ESA’s Gaia space observatory may be able to measure a wobble in the star if Jupiter-mass planets are tugging on it, but this would take years given the long orbital periods.

The TW Hydrae data are from Hubble’s Space Telescope Imaging Spectrograph. The NASA/ESA/CSA James Webb Space Telescope’s infrared vision may also be able to show the shadows in more detail.

Hubble images TW Hydrae Disc Shadows (clean). Comparison images from the NASA/ESA Hubble Space Telescope, taken several years apart, have uncovered two eerie shadows moving counterclockwise across a disc of gas and dust disc encircling the young star TW Hydrae. The discs are tilted face-on as seen from Earth and so give astronomers a bird’s-eye view of what’s happening around the star. The left image, taken in 2016, shows just one shadow at the 11 o’clock position. This shadow is cast by an inner disc that is slightly inclined to the outer disc and so blocks starlight. The picture on the left shows a second shadow that emerged from yet another nested disc at the 7 o’clock position, as photographed in 2021. The shadows rotate around the star at different rates like the hands of a clock. They are evidence for two unseen planets that have pulled dust into their orbits. This makes them slightly inclined to each other. This is a-visible light photo taken with the Space Telescope Imaging Spectrograph. Artificial colour has been added to enhance details. Credit: NASA, ESA, J. Debes STScI

Press release from ESA Hubble.

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JWST reveals new details in Cassiopeia A

By ScientifiCult 7 April 2023

The James Webb Space Telescope reveals new details in supernova remnant Cassiopeia A (Cas A)

The explosion of a star is a dramatic event, but the remains that the star leaves behind can be even more dramatic. A new mid-infrared image from NASA/ESA/CSA James Webb Space Telescope provides one stunning example. It shows the supernova remnant Cassiopeia A (Cas A), created by a stellar explosion 340 years ago. The image displays vivid colours and intricate structures begging to be examined more closely. Cas A is the youngest known remnant of an exploding, massive star in our galaxy, offering astronomers an opportunity to perform stellar forensics to understand the star’s death.

Cassiopeia A is a prototypical supernova remnant that has been widely studied by a number of ground-based and space-based observatories. The multi-wavelength observations can be combined to provide scientists with a more comprehensive understanding of the remnant.

The striking colours of the new Cas A image, in which infrared light is translated into visible-light wavelengths, hold a wealth of scientific information that researchers are just beginning to tease out. On the bubble’s exterior, particularly at the top and left, lie curtains of material appearing orange and red that are due to emission from warm dust. This marks where ejected material from the exploded star is ramming into surrounding circumstellar gas and dust.

JWST reveals new details in Cassiopeia A: Cassiopeia A (Cas A) is a supernova remnant located about 11 000 light-years from Earth in the constellation Cassiopeia. It spans approximately 10 light-years. This new image uses data from Webb’s Mid-InfraRed Instrument (MIRI) to reveal Cas A in a new light.
On the remnant’s exterior, particularly at the top and left, lie curtains of material appearing orange and red that are due to emission from warm dust. This marks where ejected material from the exploded star is ramming into surrounding circumstellar material.
Interior to this outer shell lie mottled filaments of bright pink studded with clumps and knots. This represents material from the star itself, and likely shines by the light produced by a mix of heavy elements and dust emission. The stellar material can also be seen as fainter wisps near the cavity’s interior.
A loop represented in green extends across the right side of the central cavity. Its shape and complexity are unexpected and challenging for scientists to understand.
This image combines data from various filters, with the colour red assigned to 25.5 microns (F2550W), orange-red to 21 microns (F2100W), orange to 18 microns (F1800W), yellow to 12.8 microns (F1280W), green to 11.3 microns (F1130W), cyan to 10 microns (F1000W), light blue to 7.7 microns (F770W), and blue to 5.6 microns (F560W). The data come from the general observer program 1947.
Credit:
NASA, ESA, CSA, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (UGent), J. DePasquale (STScI)

Interior to this outer shell lie mottled filaments of bright pink studded with clumps and knots. This represents material from the star itself, which is shining by the light produced by a mix of heavy elements, such as oxygen, argon, and neon, as well as dust emission. The stellar material can also be seen as fainter wisps near the cavity’s interior.

Among the science questions that Cas A may help answer is: where does cosmic dust come from? Observations have found that even very young galaxies in the early Universe are suffused with massive quantities of dust. It’s difficult to explain the origins of this dust without invoking supernovae, which spew large quantities of heavy elements (the building blocks of dust) across space.

However, existing observations of supernovae have been unable to conclusively explain the amount of dust we see in those early galaxies. By studying Cas A with Webb, astronomers hope to gain a better understanding of its dust content, which can help inform our understanding of where the building blocks of planets — and ourselves — are created.

Supernovae like the one that formed Cas A are crucial for life as we know it. They spread elements like the calcium we find in our bones and the iron in our blood across interstellar space, seeding new generations of stars and planets.

The Cas A remnant spans about 10 light-years and is located 11 000 light-years away in the constellation Cassiopeia.

JWST reveals new details in supernova remnant Cassiopeia A — JWST reveals new details in Cassiopeia A: Cassiopeia A (Cas A) is a supernova remnant located about 11,000 light-years from Earth in the constellation Cassiopeia. It spans approximately 10 light-years. This new image uses data from Webb’s Mid-Infrared Instrument (MIRI) to reveal Cas A in a new light.
On the remnant’s exterior, particularly at the top and left, lie curtains of material appearing orange and red due to emission from warm dust. This marks where ejected material from the exploded star is ramming into surrounding circumstellar material.
Interior to this outer shell lie mottled filaments of bright pink studded with clumps and knots. This represents material from the star itself, and likely shines due to a mix of various heavy elements and dust emission. The stellar material can also be seen as fainter wisps near the cavity’s interior.
A loop represented in green extends across the right side of the central cavity. Its shape and complexity are unexpected and challenging for scientists to understand.
This image combines various filters with the colour red assigned to 25.5 microns (F2550W), orange-red to 21 microns (F2100W), orange to 18 microns (F1800W), yellow to 12.8 microns (F1280W), green to 11.3 microns (F1130W), cyan to 10 microns (F1000W), light blue to 7.7 microns (F770W), and blue to 5.6 microns (F560W). The data comes from the general observer program 1947.
[Image description: A roughly square image is rotated clockwise about 45 degrees. Within the image is a circular-shaped nebula with complex structure. On the circle’s exterior lie curtains of material glowing orange. Interior to this outer shell lies a ring of mottled filaments of bright pink studded with clumps and knots. At center right, a greenish loop extends from the right side of the ring into the central cavity. Translucent wisps of blue, green, and red appear throughout the image.]
Credit:
NASA, ESA, CSA, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (UGent), J. DePasquale (STScI)

Press release from ESA JWST

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JWST adds another ringed world with new image of Uranus

By ScientifiCult 6 April 2023

The James Webb Space Telescope adds another ringed world with new image of Uranus

Webb’s infrared image highlights the planet’s dramatic rings and dynamic atmosphere.

Following in the footsteps of the Neptune image released in 2022, the NASA/ESA/CSA James Webb Space Telescope has taken a stunning image of the Solar System’s other ice giant, the planet Uranus. The new image features dramatic rings as well as bright features in the planet’s atmosphere. The Webb data demonstrate the observatory’s unprecedented sensitivity by revealing the faintest dusty rings, which have only ever been imaged by two other facilities: the Voyager 2 spacecraft as it flew past the planet in 1986, and the Keck Observatory with advanced adaptive optics.

The seventh planet from the Sun, Uranus is unique: it rotates on its side, at a nearly 90-degree angle from the plane of its orbit. This causes extreme seasons since the planet’s poles experience many years of constant sunlight followed by an equal number of years of complete darkness. (Uranus takes 84 years to orbit the Sun.) Currently, it is late spring at the northern pole, which is visible here; Uranus’s northern summer will be in 2028. In contrast, when Voyager 2 visited Uranus it was summer at the south pole. The south pole is now on the ‘dark side’ of the planet, out of view and facing the darkness of space.

Zoomed-in image of Uranus ringed atmosphere Webb JWST — This zoomed-in image of Uranus, captured by Webb’s Near-Infrared Camera (NIRCam) on 6 February 2023, reveals stunning views of the planet’s rings. The planet displays a blue hue in this representative-colour image, made by combining data from two filters (F140M, F300M) at 1.4 and 3.0 microns, shown here as blue and orange, respectively. On the right side of the planet is an area of brightening at the pole facing the Sun, known as a polar cap. This polar cap is unique to Uranus because it is the only planet in the Solar System that is tilted on its side, which causes its extreme seasons. A new aspect of the polar cap revealed by Webb is a subtle brightening near the Uranian north pole. At the edge of the polar cap lies a bright cloud and a few fainter extended features can be seen just beyond the cap’s edge; a second very bright cloud is seen at the planet’s left limb. Such clouds are typical for Uranus at infrared wavelengths, and are likely connected to storm activity. Credit: NASA, ESA, CSA, STScI, J. DePasquale (STScI)

This annotated, zoomed-in image of Uranus, captured by Webb’s Near-Infrared Camera (NIRCam) on 6 February 2023, reveals stunning views of the planet’s rings, as well as clouds and the polar cap. On the right side of the planet is an area of brightening at the pole facing the Sun, known as a polar cap. This polar cap is unique to Uranus because it is the only planet in the Solar System that is tilted on its side, which causes its extreme seasons. A new aspect of the polar cap revealed by Webb is a subtle brightening near the Uranian north pole. At the edge of the polar cap lies a bright cloud and a few fainter extended features can be seen just beyond the cap’s edge; a second very bright cloud is seen at the planet’s left limb. Such clouds are typical for Uranus at infrared wavelengths, and are likely connected to storm activity. The planet displays a blue hue in this representative-colour image, made by combining data from two filters (F140M, F300M) at 1.4 and 3.0 microns, which are assigned to blue and orange, respectively. Credit: NASA, ESA, CSA, STScI, J. DePasquale (STScI)

This infrared image from Webb’s Near-Infrared Camera (NIRCam) combines data from two filters at 1.4 and 3.0 microns, shown here in blue and orange, respectively. The planet displays a blue hue in the resulting representative-colour image.

When Voyager 2 looked at Uranus, its camera saw an almost featureless blue-green ball at visible wavelengths. At infrared wavelengths, and with Webb’s greater sensitivity, we see more detail, showing how dynamic the atmosphere of Uranus really is.

On the right side of the planet is an area of brightening at the pole facing the Sun, known as a polar cap. This polar cap is unique to Uranus — it seems to appear when the pole enters direct sunlight in the summer and vanishes in the autumn; these Webb data will help scientists understand the currently mysterious mechanism behind this feature. Webb has revealed a surprising aspect of the polar cap: a subtle enhanced brightening at the centre of the cap. The sensitivity of Webb’s NIRCam and the longer wavelengths it can see may explain why we can see this enhanced polar feature of Uranus when it has not been seen with other powerful telescopes like the NASA/ESA Hubble Space Telescope and the Keck Observatory.

At the edge of the polar cap lies a bright cloud and a few fainter extended features can be seen just beyond the cap’s edge; a second very bright cloud is seen at the planet’s left limb. Such clouds are typical for Uranus at infrared wavelengths, and are likely connected to storm activity.

This planet is characterised as an ice giant because of the chemical make-up of its interior. Most of its mass is thought to be a hot, dense fluid of ‘icy’ materials — water, methane and ammonia — above a small rocky core.

Uranus has 13 known rings and 11 of them are visible in this Webb image. Some of these rings are so bright as seen by Webb that when they are close together, they appear to merge into a larger ring. Nine are classed as the main rings of the planet, and two are the fainter dusty rings (such as the diffuse zeta ring closest to the planet) that weren’t discovered until the 1986 flyby by Voyager 2. Scientists expect that future Webb images of Uranus will reveal the two faint outer rings that were discovered with Hubble during the 2007 ring-plane crossing.

This wider view of the Uranian system with Webb’s NIRCam instrument features the planet Uranus as well as six of its 27 known moons (most of which are too small and faint to be seen in this short exposure). A handful of background objects, including many galaxies, are also seen. Credit: NASA, ESA, CSA, STScI, J. DePasquale (STScI)

Webb also captured many of Uranus’s 27 known moons (most of which are too small and faint to be seen here); the six brightest are identified in the wide-view image. This was only a short (12-minute) exposure image of Uranus with just two filters. It is just the tip of the iceberg of what Webb can do when observing this mysterious planet. Additional studies of Uranus are happening now, and more are planned in Webb’s first year of science operations.

Press release from ESA JWST

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Webb measures the temperature of the rocky exoplanet TRAPPIST-1 b

By ScientifiCult 27 March 2023

Webb measures the temperature of the rocky exoplanet TRAPPIST-1 b

An international team of researchers has used the NASA/ESA/CSA James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat energy given off in the form of infrared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s dayside has a temperature of about 500 kelvins (roughly 230°C), and suggests that it has no significant atmosphere. This is the first detection of any form of light emitted by an exoplanet as small and as cool as the rocky planets in our own solar system. The result marks an important step in determining whether planets orbiting small active stars like TRAPPIST-1 can sustain atmospheres needed to support life. It also bodes well for Webb’s ability to characterise temperate, Earth-sized exoplanets using MIRI.

“These observations really take advantage of Webb’s mid-infrared capability,” said Thomas Greene, an astrophysicist at NASA’s Ames Research Center and lead author on the study published today in the journal Nature. “No previous telescopes have had the sensitivity to measure such dim mid-infrared light.”

Rocky exoplanet TRAPPIST-1 b (illustration) — Illustration showing what the hot rocky exoplanet TRAPPIST-1 b could look like. TRAPPIST-1 b, the innermost of seven known planets in the TRAPPIST-1 system, orbits its star at a distance of 0.011 AU, completing one circuit in just 1.51 Earth-days. TRAPPIST-1 b is slightly larger than Earth, but has around the same density, which indicates that it must have a rocky composition. Webb’s measurement of mid-infrared light given off by TRAPPIST-1 b suggests that the planet does not have any substantial atmosphere. The star, TRAPPIST-1, is an ultracool red dwarf (M dwarf) with a temperature of only 2566 K and a mass just 0.09 times the mass of the Sun.
This illustration is based on new data gathered by Webb’s Mid-Infrared Instrument (MIRI) as well as previous observations from other ground- and space-based telescopes. Webb has not captured any images of the planet.
MIRI was developed as a partnership between Europe and the USA: the main partners are ESA, a consortium of nationally funded European institutes, the Jet Propulsion Laboratory (JPL) and the University of Arizona. The instrument was nationally funded by the European Consortium under the auspices of the European Space Agency.
Credit:
NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)

Rocky planets orbiting ultra cool red dwarfs

In early 2017, astronomers reported the discovery of seven rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40 light-years from Earth. What is remarkable about the planets is their similarity in size and mass to the inner, rocky planets of our own solar system. Although they all orbit much closer to their star than any of our planets orbit the Sun – all could fit comfortably within the orbit of Mercury – they receive comparable amounts of energy from their tiny star.

TRAPPIST-1 b, the innermost planet, has an orbital distance about one hundredth that of Earth’s and receives about four times the amount of energy that Earth gets from the Sun. Although it is not within the system’s habitable zone, observations of the planet can provide important information about its sibling planets, as well as those of other M-dwarf systems.

“There are ten times as many of these stars in the Milky Way as there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” explained Greene. “But they are also very active – they are very bright when they’re young and they give off flares and X-rays that can wipe out an atmosphere.”

Co-author Elsa Ducrot from CEA in France, who was on the team that conducted the initial studies of the TRAPPIST-1 system, added,

“It’s easier to characterise terrestrial planets around smaller, cooler stars. If we want to understand habitability around M stars, the TRAPPIST-1 system is a great laboratory. These are the best targets we have for looking at the atmospheres of rocky planets.”

Webb measures the temperature of the rocky exoplanet TRAPPIST-1 b. Light curve showing the change in brightness of the TRAPPIST-1 system as the innermost planet, TRAPPIST-1 b, moves behind the star. This phenomenon is known as a secondary eclipse.
Astronomers used Webb’s Mid-Infrared Instrument (MIRI) to measure the brightness of mid-infrared light. When the planet is beside the star, the light emitted by both the star and the dayside of the planet reach the telescope, and the system appears brighter. When the planet is behind the star, the light emitted by the planet is blocked and only the starlight reaches the telescope, causing the apparent brightness to decrease.
Astronomers can subtract the brightness of the star from the combined brightness of the star and planet to calculate how much infrared light is coming from the planet’s dayside. This is then used to calculate the dayside temperature.
The graph shows combined data from five separate observations made using MIRI’s F1500W filter, which only allows light with wavelengths ranging from 13.5-16.6 microns to pass through to the detectors. The blue squares are individual brightness measurements. The red circles show measurements that are “binned,” or averaged to make it easier to see the change over time. The decrease in brightness during the secondary eclipse is less than 0.1%. MIRI was able to detect changes as small as 0.027% (or 1 part in 3700).
This is the first thermal emission observation of TRAPPIST-1 b, or any planet as small as Earth and as cool as the rocky planets in the Solar System.
The observations are being repeated using a 12.8-micron filter in order to confirm the results and narrow down the interpretations.
MIRI was developed as a partnership between Europe and the USA: the main partners are ESA, a consortium of nationally funded European institutes, the Jet Propulsion Laboratory (JPL) and the University of Arizona. The instrument was nationally funded by the European Consortium under the auspices of the European Space Agency.
Credit:
NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)

Detecting an atmosphere (or not)

Previous observations of TRAPPIST-1 b with the NASA/ESA Hubble Space Telescope, as well as NASA’s Spitzer Space Telescope, found no evidence for a puffy atmosphere, but were not able to rule out a dense one.

One way to reduce the uncertainty is to measure the planet’s temperature. “This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Pierre-Olivier Lagage from CEA, a co-author on the paper. “If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”

The team used a technique called secondary eclipse photometry, in which MIRI measured the change in brightness from the system as the planet moved behind the star. Although TRAPPIST-1 b is not hot enough to give off its own visible light, it does have an infrared glow. By subtracting the brightness of the star on its own (during the secondary eclipse) from the brightness of the star and planet combined, they were able to successfully calculate how much infrared light is being given off by the planet.

Webb measures the temperature of the rocky exoplanet TRAPPIST-1 b. Comparison of the dayside temperature of TRAPPIST-1 b as measured using Webb’s Mid-Infrared Instrument (MIRI) to computer models showing what the temperature would be under various conditions. The models take into account the known properties of the system, including the planet’s size and density, the temperature of the star, and the planet’s orbital distance. The temperature of the dayside of Mercury is also shown for reference.
The dayside brightness of TRAPPIST-1 b at 15 microns corresponds to a temperature of about 500 K (roughly 230°C). This is consistent with the temperature assuming the planet is tidally locked (one side facing the star at all times), with a dark-coloured surface, no atmosphere, and no redistribution of heat from the dayside to the nightside.
If the heat energy from the star were distributed evenly around the planet (for example, by a circulating carbon dioxide-free atmosphere), the temperature at 15 microns would be 400 K (125°C). If the atmosphere had a substantial amount of carbon dioxide, it would emit even less 15-micron light and would appear to be even cooler.
Although TRAPPIST-1 b is hot by Earth standards, it is cooler than the dayside of Mercury, which consists of bare rock and no significant atmosphere. Mercury receives about 1.6 times more energy from the Sun than TRAPPIST-1 b does from its star.
MIRI was developed as a partnership between Europe and the USA: the main partners are ESA, a consortium of nationally funded European institutes, the Jet Propulsion Laboratory (JPL) and the University of Arizona. The instrument was nationally funded by the European Consortium under the auspices of the European Space Agency.
Credit:
NASA, ESA, CSA, J. Olmsted (STScI), T. P. Greene (NASA Ames), T. Bell (BAERI), E. Ducrot (CEA), P. Lagage (CEA)

Measuring minuscule changes in brightness

Webb’s detection of a secondary eclipse is itself a major milestone. With the star more than 1,000 times brighter than the planet, the change in brightness is less than 0.1%.

“There was also some fear that we’d miss the eclipse. The planets all tug on each other, so the orbits are not perfect,” said Taylor Bell, the post-doctoral researcher at the Bay Area Environmental Research Institute who analysed the data. “But it was just amazing: The time of the eclipse that we saw in the data matched the predicted time within a couple of minutes.”

Analysis of data from five separate secondary eclipse observations indicates that TRAPPIST-1 b has a dayside temperature of about 500 kelvins, or roughly 230°C. The team thinks the most likely interpretation is that the planet does not have an atmosphere.

“We compared the results to computer models showing what the temperature should be in different scenarios,” explained Ducrot. “The results are almost perfectly consistent with a blackbody made of bare rock and no atmosphere to circulate the heat. We also didn’t see any signs of light being absorbed by carbon dioxide, which would be apparent in these measurements.”

This research was conducted as part of Guaranteed Time Observation (GTO) program 1177, which is one of eight approved GTO and General Observer (GO) programs designed to help fully characterise the TRAPPIST-1 system. Additional secondary eclipse observations of TRAPPIST-1 b are currently in progress, and now that they know how good the data can be, the team hopes to eventually capture a full phase curve showing the change in brightness over the entire orbit. This will allow them to see how the temperature changes from the day to the nightside and confirm if the planet has an atmosphere or not.

“There was one target that I dreamed of having,” said Lagage, who worked on the development of the MIRI instrument for more than two decades. “And it was this one. This is the first time we can detect the emission from a rocky, temperate planet. It’s a really important step in the story of discovering exoplanets.”

Press release from ESA Webb.

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Hubble monitors changing weather and seasons on Jupiter and Uranus

By ScientifiCult 23 March 2023

Hubble monitors changing weather and seasons on Jupiter and Uranus

Ever since its launch in 1990, the NASA/ESA Hubble Space Telescope has been an interplanetary weather observer, keeping an eye on the ever-changing atmospheres of the largely gaseous outer planets. And it’s an unblinking eye that allows Hubble’s sharpness and sensitivity to monitor a kaleidoscope of complex activities over time. Today new images are shared of Jupiter and Uranus.

The outer planets beyond Mars do not have solid surfaces to affect weather as on Earth. And sunlight is much less able to drive atmospheric circulation. Nevertheless, these are ever-changing worlds. And Hubble – in its role as interplanetary meteorologist – is keeping track, as it does every year. Jupiter’s weather is driven from the inside out, as more heat percolates up from its interior than it receives from the Sun. This heat indirectly drives colour-change cycles in the clouds, like the cycle that’s currently highlighting a system of alternating cyclones and anticyclones. Uranus has seasons that pass by at a snail’s pace because it takes 84 years to complete one orbit about the Sun. But those seasons are extreme, because Uranus is tipped on its side. As summer approaches in the northern hemisphere, Hubble sees a growing polar cap of high-altitude photochemical haze that looks similar to the smog over cities on Earth.

Inaugurated in 2014, the Hubble Space Telescope’s Outer Planet Atmospheres Legacy (OPAL) programme has been providing us with yearly views of the giant planets. Here are some recent images.

Jupiter

Credit:
NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

The forecast for Jupiter is for stormy weather at low northern latitudes. A prominent string of alternating storms is visible, forming a ‘vortex street’ as some planetary astronomers call it. This is a wave pattern of nested cyclones and anticyclones, locked together like the alternating gears of a machine moving clockwise and counterclockwise. If the storms get close enough to each other and merge together, they could build an even larger storm, potentially rivalling the current size of the Great Red Spot. The staggered pattern of cyclones and anticyclones prevents individual storms from merging. Activity is also seen interior to these storms; in the 1990s Hubble didn’t see any cyclones or anticyclones with built-in thunderstorms, but these storms have sprung up in the last decade. Strong colour differences indicate that Hubble is seeing different cloud heights and depths as well.

The orange moon Io photobombs this view of Jupiter’s multicoloured cloud tops, casting a shadow toward the planet’s western limb. Hubble’s resolution is so sharp that it can see Io’s mottled-orange appearance, the result of its numerous active volcanoes. These volcanoes were first discovered when the Voyager 1 spacecraft flew by in 1979. The moon’s molten interior is overlaid by a thin crust through which the volcanoes eject material. Sulphur takes on various hues at different temperatures, which is why Io’s surface is so colourful. This image was taken on 12 November 2022.

Jupiter’s legendary Great Red Spot takes centre stage in this view. Though this vortex is big enough to swallow Earth, it has actually shrunk to the smallest size it has ever been according to observation records dating back 150 years. Jupiter’s icy moon Ganymede can be seen transiting the giant planet at lower right. Slightly larger than the planet Mercury, Ganymede is the largest moon in the Solar System. It is a cratered world and has a mainly water-ice surface with apparent glacial flows driven by internal heat. This image was taken on 6 January 2023.

Jupiter and its large ocean-bearing moons (Ganymede, Callisto and Europa) are the target of ESA’s Jupiter Icy Moons Explorer (Juice). Preparations are currently underway to ready Juice for liftoff from Europe’s Spaceport in French Guiana on 13 April 2023 [1].

Jupiter (November 2022 and January 2023). Credit:NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

Uranus

Planetary oddball Uranus rolls around the Sun on its side as it follows its 84-year orbit, rather than spinning in a more ’vertical’ position as Earth does. Its weirdly tilted ‘horizontal’ rotation axis is angled just eight degrees off the plane of the planet’s orbit. One recent theory proposes that Uranus once had a massive moon that gravitationally destabilised it and then crashed into it. Other possibilities include giant impacts during the formation of the planets, or even giant planets exerting resonant torques on each other over time. The consequences of Uranus’s tilt are that for stretches of time lasting up to 42 years, parts of one hemisphere are completely without sunlight. When the Voyager 2 spacecraft visited during the 1980s, the planet’s south pole was pointed almost directly at the Sun. Hubble’s latest view shows the northern pole now tipping toward the Sun.

This is a Hubble view of Uranus taken in 2014, seven years after the northern spring equinox when the Sun was shining directly over the planet’s equator, and shows one of the first images from the OPAL programme. Multiple storms with methane ice-crystal clouds appear at mid-northern latitudes above the planet’s cyan-tinted lower atmosphere. Hubble imaged the ring system edge-on in 2007, but the rings are seen starting to open up seven years later in this view. At this time, the planet had multiple small storms and even some faint cloud bands.

As seen in 2022, Uranus’s north pole shows a thickened photochemical haze that looks similar to the smog over cities. Several little storms can be seen near the edge of the polar haze boundary. Hubble has been tracking the size and brightness of the north polar cap and it continues to get brighter year after year. Astronomers are disentangling multiple effects – from atmospheric circulation, particle properties, and chemical processes — that control how the atmospheric polar cap changes with the seasons. At the Uranian equinox in 2007, neither pole was particularly bright. As the northern summer solstice approaches in 2028 the cap may grow brighter still, and will be aimed directly toward Earth, allowing good views of the rings and the north pole; the ring system will then appear face-on. This image was taken on 10 November 2022.

Uranus (November 2014 and November 2022). Credit: NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

Uranus (November 2014 and November 2022) compass image. Credit: NASA, ESA, STScI, A. Simon (NASA-GSFC), M. H. Wong (UC Berkeley), J. DePasquale (STScI)

Notes

[1] Ganymede is the main target of ESA’s Jupiter Icy Moons Explorer (Juice). As humanity’s next bold mission to the outer Solar System, Juice will complete numerous flybys around Ganymede, and eventually enter orbit around the moon. The mission will explore various key topics: Ganymede’s mysterious magnetic field, its hidden ocean, its complex core, its ice content and shell, its interactions with its local environment and that of Jupiter, its past and present activity, and whether or not the moon could be a habitable environment.

More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The HST observations featured in this release include those from program 16790, 13937 , and 16995 (A. Simon).

Press release from ESA Hubble about the telescope observing the changing weather and seasons on Jupiter and Uranus.

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Webb spots swirling, gritty clouds on VHS 1256 b, a remote planet

By ScientifiCult 22 March 2023

Webb spots swirling, gritty clouds on VHS 1256 b, a remote planet

Researchers observing with the NASA/ESA/CSA James Webb Space Telescope have pinpointed silicate cloud features in a distant planet’s atmosphere. The atmosphere is constantly rising, mixing, and moving during its 22-hour day, bringing hotter material up and pushing colder material down. The resulting brightness changes are so dramatic that it is the most variable planetary-mass object known to date. The science team also made extraordinarily clear detections of water, methane and carbon monoxide with Webb’s data, and found evidence of carbon dioxide. This is the largest number of molecules ever identified all at once on a planet outside our Solar System.

Exoplanet VHS 1256 b — This illustration conceptualises the swirling clouds identified by the James Webb Space Telescope in the atmosphere of the exoplanet VHS 1256 b. The planet is about 40 light-years away and orbits two stars that are locked in their own tight rotation. Its clouds, which are filled with silicate dust, are constantly rising, mixing, and moving during its 22-hour day.
Credit:
NASA, ESA, CSA, J. Olmsted (STScI)

Catalogued as VHS 1256 b, the planet is about 40 light-years away and orbits not one, but two stars over a 10 000-year period.

“VHS 1256 b is about four times farther from its stars than Pluto is from our Sun, which makes it a great target for Webb,” said science team lead Brittany Miles of the University of Arizona. “That means the planet’s light is not mixed with light from its stars.” Higher up in its atmosphere, where the silicate clouds are churning, temperatures reach a scorching 830 degrees Celsius.

Within those clouds, Webb detected both larger and smaller silicate dust grains, which are shown on a spectrum.

“The finer silicate grains in its atmosphere may be more like tiny particles in smoke,” noted co-author Beth Biller of the University of Edinburgh in the United Kingdom. “The larger grains might be more like very hot, very small sand particles.”

VHS 1256 b has low gravity compared to more massive brown dwarfs [1], which means that its silicate clouds can appear and remain higher in its atmosphere where Webb can detect them. Another reason its skies are so turbulent is the planet’s age. In astronomical terms, it’s quite young. Only 150 million years have passed since it formed — and it will continue to change and cool over billions of years.

In many ways, the team considers these findings to be the first ‘coins’ pulled out of a spectrum that researchers view as a treasure chest of data. In many ways, they’ve only begun identifying its contents.

“We’ve identified silicates, but a better understanding of which grain sizes and shapes match specific types of clouds is going to take a lot of additional work,” Miles said. “This is not the final word on this planet — it is the beginning of a large-scale modelling effort to fit Webb’s complex data.”

Although all of the features the team observed have been spotted on other planets elsewhere in the Milky Way by other telescopes, other research teams typically identified only one at a time.

“No other telescope has identified so many features at once for a single target,” said co-author Andrew Skemer of the University of California, Santa Cruz. “We’re seeing a lot of molecules in a single spectrum from Webb that detail the planet’s dynamic cloud and weather systems.”

The team came to these conclusions by analysing data known as spectra gathered by two instruments aboard Webb, the Near-Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument (MIRI). Since the planet orbits at such a great distance from its stars, the researchers were able to observe it directly, rather than using the transit technique [2] or a coronagraph [3] to take this data.

There will be plenty more to learn about VHS 1256 b in the months and years to come as this team — and others — continue to sift through Webb’s high-resolution infrared data. “There’s a huge return on a very modest amount of telescope time,” Biller added. “With only a few hours of observations, we have what feels like unending potential for additional discoveries.”

What might become of this planet billions of years from now? Since it’s so far from its stars, it will become colder over time, and its skies may transition from cloudy to clear.

The researchers observed VHS 1256 b as part of Webb’s Early Release Science program, which is designed to help transform the astronomical community’s ability to characterise planets and the discs from which they form.

The team’s paper, entitled “The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b,” will be published in The Astrophysical Journal Letters on 22 March.

Press release from ESA Webb.

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Webb captures rarely seen prelude to a supernova

By ScientifiCult 14 March 2023

A Wolf-Rayet star is a rare prelude to the famous final act of a massive star: the supernova. As one of its first observations in 2022, the NASA/ESA/CSA James Webb Space Telescope captured the Wolf-Rayet star WR 124 in unprecedented detail. A distinctive halo of gas and dust frames the star and glows in the infrared light detected by Webb, displaying knotty structure and a history of episodic ejections. Despite being the scene of an impending stellar ‘death’, astronomers also look to Wolf-Rayet stars for insight into new beginnings. Cosmic dust is forming in the turbulent nebulas surrounding these stars, dust that is composed of the heavy-element building blocks of the modern Universe, including life on Earth.

Wolf-Rayet stars are known to be efficient dust producers, and the Mid-Infrared Instrument (MIRI) on the NASA/ESA/CSA James Webb Space Telescope shows this to great effect. Cooler cosmic dust glows at the longer mid-infrared wavelengths, displaying the structure of WR 124’s nebula. The 10 light-years-wide nebula is made of material cast off from the ageing star in random ejections, and from dust produced in the ensuing turbulence. This brilliant stage of mass loss precedes the star’s eventual supernova, when nuclear fusion in its core stops and the pressure of gravity causes it to collapse in on itself, and then explode. As MIRI demonstrates here, Webb will help astronomers to explore questions that were previously only available to theory, questions like how much dust stars like this create before exploding in a supernova, and how much of that dust is large enough to survive the blast and go on to serve as a building block of future stars and planets.
In this image red is assigned to wavelengths of 12.8 and 18 microns (F1280W, F1800W), green to 11.3 microns (F1130W), and blue to 7.7 microns (F770W).
Credit:
NASA, ESA, CSA, STScI, Webb ERO Production Team

The rare sight of a Wolf-Rayet star — among the most luminous, most massive, and most briefly-detectable stars known — was one of the first observations made by the NASA/ESA/CSA James Webb Space Telescope. Webb shows the star WR 124 in unprecedented detail with its powerful infrared instruments. The star is 15 000 light-years away in the constellation Sagitta.

Massive stars race through their life cycles, and not all of them go through a brief Wolf-Rayet phase before becoming a supernova, making Webb’s detailed observations valuable to astronomers. Wolf-Rayet stars are in the process of casting off their outer layers, resulting in their characteristic halos of gas and dust. The star WR 124 is 30 times the mass of the Sun and has shed 10 Suns-worth of material — so far. As the ejected gas moves away from the star and cools, cosmic dust forms and glows in the infrared light detectable by Webb.

The origin of cosmic dust that can survive a supernova blast and contribute to the Universe’s overall ‘dust budget’ is of great interest to astronomers for many reasons. Dust is integral to the workings of the Universe: it shelters forming stars, gathers together to help form planets, and serves as a platform for molecules to form and clump together — including the building blocks of life on Earth. Despite the many essential roles that dust plays, there is still more dust in the Universe than astronomers’ current dust-formation theories can explain. The Universe is operating with a dust budget surplus.

Wolf-Rayet WR 124 prelude to a supernova — The luminous, hot star Wolf-Rayet 124 (WR 124) is prominent at the centre of the NASA/ESA/CSA James Webb Space Telescope’s composite image combining near-infrared and mid-infrared wavelengths of light. The star displays the characteristic diffraction spikes of Webb’s Near-infrared Camera (NIRCam), caused by the physical structure of the telescope itself. NIRCam effectively balances the brightness of the star with the fainter gas and dust surrounding it, while Webb’s Mid-Infrared Instrument (MIRI) reveals the nebula’s structure.
Background stars and galaxies populate the field of view and peek through the nebula of gas and dust that has been ejected from the ageing massive star to span 10 light-years across space. A history of the star’s past episodes of mass loss can be read in the nebula’s structure. Rather than smooth shells, the nebula is formed from random, asymmetric ejections. Bright clumps of gas and dust appear like tadpoles swimming toward the star, their tails streaming out behind them, blown back by the stellar wind.
This image combines various filters from both Webb imaging instruments, with the colour red assigned to wavelengths of 4.44, 4.7, 12.8, and 18 microns (F444W, F470N, F1280W, F1800W), green to 2.1, 3.35, and 11.3 microns (F210M, F335M, F1130W), and blue to 0.9, 1.5, and 7.7 microns (F090W, F150W, F770W).
Credit:
NASA, ESA, CSA, STScI, Webb ERO Production Team

Webb opens up new possibilities for studying details in cosmic dust, which is best observed in infrared wavelengths of light. Webb’s Near-Infrared Camera (NIRCam) balances the brightness of WR 124’s stellar core and the knotty details in the fainter surrounding gas. The telescope’s Mid-Infrared Instrument (MIRI) reveals the clumpy structure of the gas and dust nebula surrounding the star. Before Webb, dust-loving astronomers simply did not have enough detailed information to explore questions of dust production in environments like WR 124, and whether that dust was of sufficient size and quantity to survive and make a significant contribution to the overall dust budget. Now those questions can be investigated with real data.

Stars like WR 124 also serve as an analogue to help astronomers understand a crucial period in the early history of the Universe. Similar dying stars seeded the young Universe with the heavy elements forged in their cores — elements that are now common in the current era, including on Earth.

Webb’s detailed image of WR 124 preserves forever a brief, turbulent time of transformation, and promises future discoveries that will reveal the long-shrouded mysteries of cosmic dust.

Press release from ESA Webb.

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