Space & Astronomy

A fast-spinning neutron star south of the constellation Leo is the most massive of its kind seen so far, according to new observations.

The record-setting collapsed star, named PSR J0952-0607, weighs about 2.35 times as much as the sun, researchers report July 11 on arXiv.org. “That’s the heaviest well-measured neutron star that has been found to date,” says study coauthor Roger Romani, an astrophysicist at Stanford University.

The previous record holder was a neutron star in the northern constellation Camelopardalis named PSR J0740+6620, which tipped the scales at about 2.08 times as massive as the sun. If a neutron star grows too massive, it collapses under its own weight and becomes a black hole. These measurements of hefty neutron stars are of interest because no one knows the exact mass boundary between neutron stars and black holes.

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That dividing line drives the quest to find the most massive neutron stars and determine just how massive they can be, Romani says. “It’s defining the boundary between the visible things in the universe and the stuff that is forever hidden from us inside of a black hole,” he says. “A neutron star that’s on the hairy edge of becoming a black hole — just about heavy enough to collapse — has at its center the very densest material that we can access in the entire visible universe.”

PSR J0952-0607 is in the constellation Sextans, just south of Leo. It resides 20,000 light-years from Earth, far above the galaxy’s plane in the Milky Way’s halo. The neutron star emits a pulse of radio waves toward us each time it spins, so astronomers also classify the object as a pulsar. First reported in 2017, this pulsar spins every 1.41 milliseconds, faster than all but one other pulsar.

That’s why Romani and his colleagues chose to study it — the fast spin led them to suspect that the pulsar might be unusually heavy. That’s because another star orbits the pulsar, and just as water spilling over a water wheel spins it up, gas falling from that companion onto the pulsar could have sped up its rotation while also boosting its mass.

Observing the companion, Romani and his colleagues found that it whips around the pulsar quickly — at about 380 kilometers per second. Using the companion’s speed and its orbital period of about six and a half hours, the team calculated the pulsar’s mass to be more than twice the mass of the sun. That’s a lot heavier than the typical neutron star, which is only about 1.4 times as massive as the sun.

“It’s a terrific study,” says Emmanuel Fonseca, a radio astronomer at West Virginia University in Morgantown who measured the mass of the previous record holder but was not involved in the new work. “It helps nuclear physicists actually constrain the nature of matter within these extreme environments.” More

Massimo Pascale wasn’t planning to study the galaxy cluster SMACS 0723. But as soon as he saw the cluster glittering in the first image from the James Webb Space Telescope, or JWST, he and his colleagues couldn’t help themselves.

“We were like, we have to do something,” says Pascale, an astronomer at the University of California, Berkeley. “We can’t stop ourselves from analyzing this data. It was so exciting.”

Pascale’s team is one of several groups of scientists who saw the first JWST images and immediately rolled up their sleeves. In the first few days after images and the data used to create them were made public, scientists have estimated the amount of mass the cluster contains, uncovered a violent incident in the cluster’s recent past and estimated the ages of the stars in galaxies far beyond the cluster itself.

“We’ve been preparing for this for a long time. Myself, I’ve been preparing for years, and I’m not very old,” says Pascale, who is in his fourth year of graduate school.  JWST “is really going to define a new generation of astronomers and a new generation of science as a whole.”

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Cluster collision

When the image of SMACS 0723 was released in a White House briefing on July 11, most of the focus went to extremely distant galaxies in the background (SN: 7/11/22). But smack in the middle of the image is SMACS 0723 itself, a much closer cluster of galaxies about 4.6 billion light-years from Earth. Its mass bends light from even farther away, making more distant objects appear magnified, as if their light had traveled through the lens of another cosmic-sized telescope.

The light from the most distant galaxy in this image started its journey to JWST about 13.3 billion years ago — “almost at the dawn of the universe,” says astrophysicist Guillaume Mahler of Durham University in England, who is already using the picture as his Zoom background.

But the image can also fill in the history of the intervening galaxy cluster itself. “People sometimes forget about that — the galaxy cluster is also very important,” Pascale says.

Pascale’s and Mahler’s teams each started by taking inventory of the distant galaxies that appear stretched and distorted in the image. The light from some of those galaxies is warped such that multiple images of the same galaxy appear in different places. Mapping those multiply imaged galaxies is a sensitive probe of the way mass is spread around the cluster. That, in turn, can reveal where the cluster contains dark matter, the invisible, mysterious substance that makes up the majority of the mass in the universe (SN: 9/10/20).

Both teams found that SMACS 0723 is more elongated than it appeared in previous observations. They also found a faint glow, called intracluster light, inside the cluster from stars that don’t belong to any particular galaxy. Together, those features suggest that SMACS 0723 is still recovering from a relatively recent smash-up with another galaxy cluster, the teams report separately in a pair of papers submitted to arXiv.org on July 14.

A galaxy cluster that has been sitting on its own for eons should have a rounder distribution of matter and intracluster light, rather than SMACS 0723’s oblong shape. The stars that emit the intracluster light were probably ripped from their home galaxies by gravitational forces during the collision.

“Two separate clusters have merged together, and it looks to us as if it’s not totally settled yet,” Pascale says. “What we might be looking at is an ongoing merger.”

Three examples of multiply imaged galaxies — marked with white, red and yellow arrows — popped out of this small region of the first JWST image. The gravity from a foreground galaxy cluster distorted the light from these galaxies, making them appear in at least two places at once.Reproduced from M. Pascale et al/arXiv.org 2022

Far-flung galaxies

Mapping out mass in the cluster is also essential to decoding the properties of the more distant galaxies in the background of the image, Mahler says. “You need to understand the cluster and its magnification power to understand what’s behind.”

Some scientists are already investigating those distant galaxies in detail. The first JWST data include not just pretty pictures but also spectra, measurements of how much light an object emits at various wavelengths. Spectra allow scientists to determine how much a distant object’s light has been stretched — or redshifted — by the expansion of the universe, which is a proxy for its distance. Such data can also help reveal a galaxy’s composition and the ages of its stars.

“The main thing that limits the study of star formation in galaxies is the quality of the data,” says astrophysicist Adam Carnall of the University of Edinburgh. But with the vastly improved data from JWST, he says, he and his team were able to measure the ages of stars in those remote galaxies.

Carnall and colleagues turned their attention to the spectra of the distant galaxies just a few days after the SMACS image was released. They measured the redshifts of 10 galaxies, five of which were particularly distant, the team reports in a paper submitted to arXiv.org on July 18. One had already been highlighted as one of the most distant galaxy ever seen, with light that was emitted just 500 million years after the Big Bang 13.8 billion years ago. The other four shone as late as 1.1 billion years after the Big Bang.

All 10 galaxies were relatively young when they emitted the light captured by JWST, Carnall says. They had all switched on their star formation just a few million years earlier. That’s not especially surprising, but it is interesting.

“The ability to look at these small, faint galaxies … gives you a sense of how all galaxies must look when they start forming stars,” Carnall says.

Scientists hope to use JWST to find the first instances of star formation ever. Other early results suggest they’re already getting close.

Some galaxies in a JWST image of another cluster may hearken from an even earlier time, as early as 300 million years after the Big Bang, two research teams report in a pair of papers submitted to arXiv.org on July 19. One of those galaxies seems to have already built up a spiral disk about a billion times the mass of the sun, which is surprisingly mature for such an early galaxy.

And a tally of galaxies seen in the SMACS 0723 image suggests that galaxies with mature disks, rather than disorganized blobs or ones made up mostly of dark matter, may have been more common in the very early universe than previously thought, another team reports in an arXiv.org paper submitted July 19. That means those early disks might not be outliers.

“Definitely these galaxies are a big deal, but it remains to be seen how exciting they will look in the context of a few months’ progress with JWST,” Carnall says. The best is yet to come.

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Exploded stars, colliding galaxies, and beautiful clouds feature in the first space photos released by The James Webb Space Telescope July 12. More

Huge bubbles of plasma billowing out from the Milky Way’s center might contain scraps from all over the galaxy — and beyond.

A new look at gas clouds in the galaxy’s Fermi bubbles shows that the clouds contain stuff from the galaxy’s starry disk and from some mysterious other source. The finding could shed light on how galaxies in general live and die, astronomers report July 18 in Nature Astronomy.

The Fermi bubbles are giant blobs of plasma, tens of thousands of light-years tall, that extend on either side of the Milky Way’s galactic disk. When the bubbles were discovered in 2010, astronomers thought they could have been formed by newborn stars (SN: 11/9/10). These days, many astronomers are instead convinced the bubbles could have been blown by a massive, long-ago burp emitted from the galaxy’s supermassive black hole.

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In the years that followed the discovery, astronomers also spotted clouds of relatively cool gas that seem to flit around within the bubbles, high above the starry disk. “We call them high velocity clouds, because we’re not very good at naming things,” says astrophysicist Trisha Ashley of the Space Telescope Science Institute in Baltimore.

Scientists thought the clouds had been ripped from the Milky Way’s bright starry disk and sent flying when the Fermi bubbles formed. That assumption has been used to calculate things like the age of the bubbles, which could offer a clue to their origins.

“It made sense, it was a logical assumption,” Ashley says. “But no one had ever tested the origin of these clouds.”

Now Ashley and colleagues have made a first effort to figure out where the clouds come from — and found a surprising answer.

Using new and archived data from several telescopes, she and her team measured the metal content — the abundances of all the elements heavier than helium — in 12 high velocity clouds entrenched in the Fermi bubbles. Then the researchers compared the clouds’ chemistries to those of stars in the Milky Way’s disk. If the clouds really did come from the disk, they should have metal contents like the sun and other disk stars, Ashley says. If not, their metal contents should be lower.

The team found a wide range of metals in the clouds, from less than a fifth of the sun’s to more than the sun’s. That means “these clouds have to originate in both the disk of the Milky Way and the halo of the Milky Way,” she says, referring to the chaotic cloud of gas and dust that surrounds the galaxy and provides it with fuel for new stars (SN: 7/12/18). “We haven’t figured out any other explanation.”

How those clouds got into the halo in the first place is still an open question, says Jessica Werk, an astronomer at the University of Washington in Seattle who was not involved in the study.

“There’s a number of ways these clouds can be produced, a number of origins and a number of fates,” she says. The clouds could have condensed within the halo on their own, or they could have been ripped from smaller galaxies cannibalized by the Milky Way, or a number of other origin stories (SN: 7/24/02). “This cycle in general is a very messy process.”

That messiness could help predict how the Milky Way’s star formation could change in the future. Cold gas clouds like these are the fuel for future star formation. If these clouds were born in the Milky Way’s gaseous halo but are being buoyed up by the Fermi bubbles instead of falling into the disk to form stars, that could eventually slow down the Milky Way’s star forming factories.

But if the gas clouds do end up forming new stars, that could mean the Milky Way is building new stars from a variety of cosmic sources.

“Ultimately what people are interested in is, how does the Milky Way sustain its star formation for a long time?” Werk says. “This tells you it’s not just one thing.”

Studying these bubbles and clouds can help astronomers understand other galaxies, too.

“We can see these things going on in other galaxies,” Ashley says. “But we have a front row seat to this one.” More

An unusual blast of radio waves from deep space had a sense of rhythm. Over the few seconds in December 2019 when the burst was detected, it kept a steady beat. That tempo holds clues to the potential origin of the mysterious outburst, one of a class of flares called fast radio bursts.

Of the hundreds of previously detected fast radio bursts, most last for mere milliseconds. But this one persisted for roughly three seconds, Daniele Michilli and colleagues report in the July 14 Nature. The burst consisted of multiple brief pulses, repeating about every two-tenths of a second.

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Scientists have previously observed fast radio bursts that repeat with a delay of minutes or days (SN: 3/2/16). “With this one it was a train of [pulses] one after the other, a heartbeat, like, ‘boom boom boom boom,’” says Michilli, an astronomer at MIT.

That makes this fast radio burst very special, says astrophysicist Bing Zhang of the University of Nevada, Las Vegas, who was not involved with the research. Compared with other fast radio bursts, “this is a different animal.”

Scientists still don’t know how fast radio bursts are generated, but evidence has been building that they are associated with ultradense, spinning dead stars called neutron stars and, in particular, highly magnetic neutron stars called magnetars (SN: 6/4/20).

The steady repetition rate hints at what may have caused this particular blast, discovered by the Canadian Hydrogen Intensity Mapping Experiment, a radio telescope in British Columbia.

Only certain types of cosmic processes produce such metronome-like signals. Neutron stars, for example, can appear to pulse as they spin, because they emit beams of radio waves that can sweep past Earth at regular intervals. Neutron stars tend to have tempos similar to that of the pulsating fast radio burst. But that burst was much more luminous than normal neutron star pulses, suggesting some unknown process would need to have amped up the emission.

Another idea is that large outbursts on magnetars could cause starquakes that jostle those stars’ solid crusts, generating regular barrages of radio waves. The rhythmic burst’s pulsing “is sort of consistent with a frequency with which we expect that magnetars could be shaking,” says astrophysicist Cecilia Chirenti of the University of Maryland in College Park, who was not involved with the new study.

Or the pulsing might result from two neutron stars that orbit one another. Outbursts could occur at regular points in that orbit, when the magnetic regions that surround each neutron star interact.

Scientists don’t know if all fast radio bursts are generated in the same way. An outlier like this one might have a different origin story than a more standard, one-off blast. That means it’s hard to make conclusions about other fast radio bursts, Zhang says. “Whatever we can derive from this one, I would not easily extrapolate to the other guys.” More

There is a galaxy spinning like a record in the early universe — far earlier than any others have been seen twirling around.  

Astronomers have spotted signs of rotation in the galaxy MACS1149-JD1, JD1 for short, which sits so far away that its light takes 13.3 billion years to reach Earth. “The galaxy we analyzed, JD1, is the most distant example of a rotational galaxy,” says astronomer Akio Inoue of Waseda University in Tokyo.

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“The origin of the rotational motion in galaxies is closely related to a question: how galaxies like the Milky Way formed,” Inoue says. “So, it is interesting to find the onset of rotation in the early universe.”

JD1 was discovered in 2012. Due to its great distance from Earth, its light had been stretched, or redshifted, into longer wavelengths, thanks to the expansion of the universe. That redshifted light revealed that JD1 existed just 500 million years after the Big Bang.

Astronomers used light from the entire galaxy to make that measurement. Now, using the Atacama Large Millimeter/submillimeter Array in Chile for about two months in 2018, Inoue and colleagues have measured more subtle differences in how that light is shifted across the galaxy’s disk. The new data show that, while all of JD1 is moving away from Earth, its northern part is moving away slower than the southern part. That’s a sign of rotation, the researchers report in the July 1 Astrophysical Journal Letters.

JD1 spins at about 180,000 kilometers per hour, roughly a quarter the spin speed of the Milky Way. The galaxy is also smaller than modern spiral galaxies. So JD1 may be just starting to spin, Inoue says.

The James Webb Space Telescope will observe JD1 in the next year to reveal more clues to how that galaxy, and others like ours, formed (SN: 10/6/21). More

We’ve now seen farther, deeper and more clearly into space than ever before.

A stellar birthplace, a nebula surrounding a dying star, a group of closely interacting galaxies, the first spectrum of an exoplanet’s light. These are some of the first images from the James Webb Space Telescope, released in a NASA news briefing on July 12. This quartet of cosmic scenes follows on the heels of the very first image released from the telescope, a vista of thousands of distant galaxies, presented in a White House briefing on July 11.   

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“First of all, it’s really gorgeous. And it’s teeming with galaxies,” said JWST Operations Scientist Jane Rigby at the July 12 briefing. “That’s been true of every image we’ve taken with Webb. We can’t take [an image of] blank sky. Everywhere we look, there’s galaxies everywhere.”

Going deep

The galaxies captured in the first released image lie behind a cluster of galaxies about 4.6 billion light-years away. The mass from those closer galaxies distorts spacetime in such a way that objects behind the cluster are magnified, giving astronomers a way to peer more than 13 billion years into the early universe.

Even with that celestial assist, other existing telescopes could never see so far.  But the James Webb Space Telescope, also known as JWST, is incredibly large — at 6.5 meters across, its mirror is nearly three times as wide as that of the Hubble Space Telescope. It also sees in the infrared wavelengths of light where distant galaxies appear. Those features give it an edge over previous observatories.

“There’s a sharpness and a clarity we’ve never had,” said Rigby, of NASA’s Goddard Space Flight Center in Greenbelt, Md. “You can really zoom in and play around.”

This composite of images, revealing thousands of galaxies, is the deepest view of the universe ever captured — a record astronomers don’t expect to last long.NASA, ESA, CSA, STScI

Although that first image represents the deepest view of the cosmos to date, “this is not a record that will stand for very long,” astronomer Klaus Pontoppidan of the Space Telescope Science Institute in Baltimore said in a June 29 news briefing. “Scientists will very quickly beat that record and go even deeper.”

But JWST wasn’t built only to peer deeper and farther back in time than ever before. The cache of first images and data showcases space scenes both near and far, glimpses of single stars and entire galaxies, and even a peek into the chemical composition of a far-off planet’s atmosphere. 

“These are pictures just taken over a period of five days. Every five days, we’re getting more data,” European Space Agency science advisor Mark McCaughrean said at the July 12 briefing. (JWST is an international collaboration among NASA, ESA and the Canadian Space Agency.) “It’s a culmination of decades of work, but it’s just the beginning of decades. What we’ve seen today with these images is essentially that we’re ready now.”

This Hubble Space Telescope image of the galaxy cluster SMACS 0723 shows the same spot of sky as the JWST image above. The visible galaxies are fewer and not as far away.NASA, ESA, HST/STScI/AURA

Cosmic cliffs

This image shows the “Cosmic Cliffs,” part of the enormous Carina nebula, a region about 7,600 light-years from Earth where many massive stars are being born. Some of the most famous Hubble Space Telescope images feature this nebula in visible light, but JWST shows it in “infrared fireworks,” Pontoppidan says. JWST’s infrared detectors can see through dust, so the nebula appears especially spangled with stars. 

Newborn stars sculpt the gas and dust around them in this JWST image of the Cosmic Cliffs in the Carina nebula, a star-forming region in the Milky Way galaxy.NASA, ESA, CSA, STScI

“We’re seeing brand new stars that were previously completely hidden from our view,” said NASA Goddard astrophysicist Amber Straughn.

But molecules in the dust itself are glowing too. Energetic winds from baby stars in the top of the image are pushing and sculpting the wall of gas and dust that runs across the middle. “We see examples of bubbles and cavities and jets that are being blown out from newborn stars,” Straughn said. And gas and dust are the raw material for new stars — and new planets.

“It reminds me that our sun and our planets, and ultimately us, were formed out of this same stuff that we see here,” Straughn said. “We humans really are connected to the universe. We’re made out of the same stuff.”

This view of young stars sculpting the gas and dust around them in the Carina nebula was captured by the Hubble space telescope in 2010.NASA, ESA, Mario Livio and Hubble 20th Anniversary Team/STScI

Foamy nebula 

The Southern Ring nebula is an expanding cloud of gas that surrounds a dying star about 2,000 light-years from Earth. In previous Hubble images, the nebula looks like an oblong swimming pool with a fuzzy orange deck and a bright diamond, a white dwarf star, in the middle. JWST expands the view far beyond that, showing more tendrils and structures in the gas than previous telescopes could see.

JWST captured an image of the Southern Ring nebula in near-infrared (left) and mid-infrared (right) light, highlighting wispy structures at the nebula’s edge and revealing a second star in the middle.NASA, ESA, CSA, STScI

“You see this bubbly, almost foamy appearance,” said JWST astronomer Karl Gordon, of the Space Telescope Science Institute. In the left hand image, which captures near-infrared light from JWST’s NIRCam instrument, the foaminess traces molecular hydrogen that formed as dust expanded away from the center. The center appears blue due to hot ionized gas heated by the leftover core of the star. Rays of light escape the nebula like the sun peeking through patchy clouds.

In the right-hand image, taken by the MIRI mid-infrared camera, the outer rings look blue and trace hydrocarbons forming on the surface of dust grains. The MIRI image also reveals a second star in the nebula’s core.

“We knew this was a binary star, but we didn’t see much of the actual star that produced this nebula,” Gordon said. “Now in MIRI this star glows red.”

Hubble took this image of the Southern Ring nebula, a cloud of gas fleeing a dying star, in 2008.NASA, The Hubble Heritage Team/STScI/AURA/NASA

A galactic quintet 

Stephan’s Quintet is a group of galaxies about 290 million light-years away that was discovered in 1877. Four of the galaxies are engaged in an intimate gravitational dance, with one member of the group passing through the core of the cluster. (The fifth galaxy is actually much closer to Earth and just appears in a similar spot on the sky.) JWST’s images show off more structure within the galaxies than previous observations did, revealing where stars are being born.

This composite image of Stephan’s Quintet shows five galaxies in mid- and near-infrared light. Four of the galaxies are bound by each others’ gravity in an endless looping dance. The fifth, the large galaxy to the left, is in the foreground, much closer to Earth than the other four. NASA, ESA, CSA, STScI

“This is a very important image and area to study,” because it shows the sort of interactions that drive the evolution of galaxies, said JWST scientist Giovanna Giardino of the European Space Agency.

In an image from the MIRI instrument alone, the galaxies look like wispy skeletons reaching towards each other. Two galaxies are clearly close to merging. And in the top galaxy, evidence of a supermassive black hole comes to light. Material swirling around the black hole is heated to extremely high temperatures and glows in infrared light as it falls into the black hole.

This Hubble space telescope image of the five galaxies that make up Stephan’s Quintet was released in 2018.G. Bacon, J. DePasquale, F. Summers and Z. Levay/STScI, NASA, ESA

An exoplanet’s sky

This “image” is clearly different from the others, but it’s no less scientifically exciting. It shows the spectrum of light from the star WASP 96 as it passes through the atmosphere of its gas giant planet, WASP 96b. 

“You get a bunch of what looks like bumps and wiggles to some people but it’s actually full of information content,” said NASA exoplanet scientist Knicole Colón. “You’re actually seeing bumps and wiggles that indicate the presence of water vapor in the atmosphere of this exoplanet.”

The planet is about half the mass of Jupiter and orbits its star every 3.4 days. Previously astronomers thought it had no clouds in its sky, but the new data from JWST show signs of clouds and haze. “There is evidence of clouds and hazes because the water features are not quite as large as we predicted,” Colón said.

Gas giant planet WASP 96b, shown in this artist’s illustration, orbits its star every 3.4 days.Engine House

A long time coming

These first images and data have been a very long time coming. The telescope that would become JWST was first dreamed up in the 1980s, and the planning and construction suffered years of budget issues and delays (SN: 10/6/21).

The telescope finally launched on December 25. It then had to unfold and assemble itself in space, travel to a gravitationally stable spot about 1.5 million kilometers from Earth, align its insectlike primary mirror made of 18 hexagonal segments and calibrate its science instruments (SN: 1/24/22). There were hundreds of possible points of failure in that process, but the telescope unfurled successfully and got to work.

“We are so thrilled that it works because there’s so much at risk,” says JWST senior project scientist John Mather of NASA’s Goddard Space Flight Center. “The world has trusted us to put our billions into this and make it go, and it works. So it’s an immense relief.”

The James Webb Space Telescope (illustrated) spent months unfolding and calibrating its instruments after it launched on December 25. Adriana Manrique Gutierrez/CIL/GSFC/NASA

In the months following, the telescope team released teasers of imagery from calibration, which already showed hundreds of distant, never-before-seen galaxies. But the images now being released are the first full-color pictures made from the data scientists will use to start unraveling mysteries of the universe.

“It sees things that I never dreamed were out there,” Mather says.

For the telescope team, the relief in finally seeing the first images was palpable. “It was like, ‘Oh my god, we made it!’” says image processor Alyssa Pagan, also of Space Telescope Science Institute. “It seems impossible. It’s like the impossible happened.”

In light of the expected anticipation surrounding the first batch of images, the imaging team was sworn to secrecy.  “I couldn’t even share it with my wife,” says Pontoppidan, leader of the team that produced the first color science images.  

“You’re looking at the deepest image of the universe yet, and you’re the only one who’s seen that,” he says, of the first picture released July 11. “It’s profoundly lonely.” Soon, though, the team of scientists, image processors and science writers was seeing something new every day for weeks as the telescope downloaded the first images. “It’s a crazy experience,” Pontoppidan says. “Once in a lifetime.”

For Pagan, the timing is perfect. “It’s a very unifying thing,” she says. “The world is so polarized right now. I think it could use something that’s a little bit more universal and connecting. It’s a good perspective, to be reminded that we’re part of something so much greater and beautiful.” 

JWST is just getting started as it now begins its first round of full science operations. “There’s lots more science to be done,” Mather says. “The mysteries of the universe will not come to an end anytime soon.”

[embedded content]
Exploded stars, colliding galaxies, and beautiful clouds feature in the first space photos released by The James Webb Space Telescope July 12.

Asa Stahl contributed to this story.  More

Clouds of sand can condense, grow and disappear in some extraterrestrial atmospheres. A new look at old data shows that clouds made of hot silicate minerals are common in celestial objects known as brown dwarfs.

“This is the first full contextual understanding of any cloud outside the solar system,” says astronomer Stanimir Metchev of the University of Western Ontario in London, Canada. Metchev’s colleague Genaro Suárez presented the new work July 4 at the Cool Stars meeting in Toulouse, France.

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Clouds come in many flavors in our solar system, from Earth’s puffs of water vapor to Jupiter’s bands of ammonia. Astronomers have also inferred the presence of “extrasolar clouds” on planets outside the solar system (SN: 9/11/19).

But the only extrasolar clouds that have been directly detected were in the skies of brown dwarfs — dim, ruddy orbs that are too large to be planets but too small and cool to be stars. In 2004, astronomers used NASA’s Spitzer Space Telescope to observe brown dwarfs and spotted spectral signatures of sand — more specifically, grains of silicate minerals such as quartz and olivine. A few more tentative examples of sand clouds were spotted in 2006 and 2008.

Floating in one of these clouds would feel like being in a sandstorm, says planetary scientist Mark Marley of the University of Arizona in Tucson, who was involved in one of those early discoveries. “If you could take a scoop out of it and bring it home, you would have hot sand.”

Astronomers at the time found six examples of these silicate clouds. “I kind of thought that was it,” Marley says. Theoretically, there should be a lot more than six brown dwarfs with sandy skies. But part of the Spitzer telescope ran out of coolant in 2009 and was no longer able to measure similar clouds’ chemistry.

While Suárez was looking into archived Spitzer data for a different project, he realized there were unpublished or unanalyzed data on dozens of brown dwarfs. So he analyzed all of the low-mass stars and brown dwarfs that Spitzer had ever observed, 113 objects in total, 68 of which had never been published before, the team reports in the July Monthly Notices of the Royal Astronomical Society.

“It’s very impressive to me that this was hiding in plain sight,” Marley says.

Not every brown dwarf in the sample showed strong signs of silicate clouds. But together, the brown dwarfs followed a clear trend. For dwarfs and low-mass stars hotter than about 1700˚ Celsius, silicates exist as a vapor, and the objects show no signs of clouds. But below that temperature, signs of clouds start to appear, becoming thickest around 1300˚ C. Then the signal disappears for brown dwarfs that are cooler than about 1000˚ C, as the clouds sink deep into the atmospheres.

The finding confirms previous suspicions that silicate clouds are widespread and reveals the conditions under which they form. Because brown dwarfs are born hot and cool down over time, most of them should see each phase of sand cloud evolution as they age. “We are learning how these brown dwarfs live,” Suárez says. Future research can extrapolate the results to better understand atmospheres in planets like Jupiter, he notes.

The recently launched James Webb Space Telescope will also study atmospheric chemistry in exoplanets and brown dwarfs and will specifically look for clouds (SN: 10/6/21). Marley looks forward to combining the trends from this study with future results from JWST. “It’s really going to be a renaissance in brown dwarf science,” he says. More