BY: CAMILLE M. CARLISLE
New near-infrared observations from the Webb telescope reveal intricate strands of debris from the exploded star.
NASA / ESA / CSA / STScI / Danny Milisavljevic (Purdue University) / Ilse De Looze (UGent) / Tea Temim (Princeton University)
This new infrared image from the James Webb Space Telescope reveals the intricate knots of debris inside the supernova remnant Cassiopeia A. Cas A lies about 11,000 light-years from Earth and formed more than 300 years ago when a massive star went kablooey.
Spectroscopic study of the explosion’s light echo — the reflection of the flash off surrounding dust grains — has previously revealed that the event was a Type IIb supernova, the death of a big star stripped of most of its hydrogen shell.
JWST astronomers released a different image of Cas A earlier this year (see below). That one was assembled from mid-infrared data and highlighted in reddish orange where the expanding blast wave is ramming into material surrounding the dead star. In the new image, the outer regions have instead been colored white. This is not merely an aesthetic choice but one made to highlight that we’re looking at different kinds of emission: In mid-infrared, we were detecting glowing dust; in the near-infrared image, we’re seeing emission from electrons corkscrewing along magnetic field lines at breakneck speeds.
NASA / ESA / CSA / Danny Milisavljevic (Purdue University) / Tea Temim (Princeton University) / Ilse De Looze (UGent); Image processing: Joseph DePasquale (STScI)
The most eye-catching part of the first, near-infrared image is the pinkish festoons. These strands are debris from the now-dead star and comprise sulfur, oxygen, argon, and neon. Dust sprinkles the mix. Cas A spans some 10 light-years, but some of these ejecta filaments are so small that they evade JWST’s resolution at this distance, meaning they’re at most 100 astronomical units across — roughly twice the size of the solar system, if you include the main part of the Kuiper Belt outside Neptune’s orbit.
Dust is a major player in stellar evolution. It helps cool gas, enabling it to collapse and form stars. Astronomers still question what the universe’s primary source of dust is. Some dust comes from aging, puffy giants that are sloughing off their outer layers as winds, but these don’t form rapidly enough to explain the high quantities of dust found in the early universe.
Supernovae also create dust, which forms in the cooling ejecta. The problem is, supernovae destroy the same dust they create: The shock wave created when the ejecta slam into surrounding material rebounds back into the remnant’s interior, heating and destroying dust as it goes.
The highly clumpy nature of ejecta that JWST is revealing could explain how dust survive this process: Grains may shelter deep inside the clumps, away from the shock wave’s destructive effects.
NASA’s Webb stuns with new high-definition look at exploded star
Reports and ProceedingsIMAGE:
NASA’S JAMES WEBB SPACE TELESCOPE’S NEW VIEW OF CASSIOPEIA A (CAS A) IN NEAR-INFRARED LIGHT IS GIVING ASTRONOMERS HINTS AT THE DYNAMICAL PROCESSES OCCURRING WITHIN THE SUPERNOVA REMNANT. TINY CLUMPS REPRESENTED IN BRIGHT PINK AND ORANGE MAKE UP THE SUPERNOVA’S INNER SHELL, AND ARE COMPRISED OF SULFUR, OXYGEN, ARGON, AND NEON FROM THE STAR ITSELF. A LARGE, STRIATED BLOB AT THE BOTTOM RIGHT CORNER OF THE IMAGE, NICKNAMED BABY CAS A, IS ONE OF THE FEW LIGHT ECHOES VISIBLE NIRCAM’S FIELD OF VIEW. IN THIS IMAGE, RED, GREEN, AND BLUE WERE ASSIGNED TO WEBB’S NIRCAM DATA AT 4.4, 3.56, AND 1.62 MICRONS (F444W, F356W, AND F162M, RESPECTIVELY).
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CREDIT: NASA, ESA, CSA, STSCI, D. MILISAVLJEVIC (PURDUE UNIVERSITY), T. TEMIM (PRINCETON UNIVERSITY), I. DE LOOZE (UNIVERSITY OF GENT)
Like a shiny, round ornament ready to be placed in the perfect spot on a holiday tree, supernova remnant Cassiopeia A (Cas A) gleams in a new image from NASA’s James Webb Space Telescope. As part of the 2023 Holidays at the White House, First Lady of the United States Dr. Jill Biden debuted the first-ever White House Advent Calendar. To showcase the “Magic, Wonder, and Joy” of the holiday season, Dr. Biden and NASA are celebrating with this new image from Webb.
While all is bright, this scene is no proverbial silent night. Webb’s NIRCam (Near-Infrared Camera) view of Cas A displays this stellar explosion at a resolution previously unreachable at these wavelengths. This high-resolution look unveils intricate details of the expanding shell of material slamming into the gas shed by the star before it exploded.
Cas A is one of the most well-studied supernova remnants in all of the cosmos. Over the years, ground-based and space-based observatories, including NASA’s Chandra X-Ray Observatory, Hubble Space Telescope, and retired Spitzer Space Telescope have assembled a multiwavelength picture of the object’s remnant.
However, astronomers have now entered a new era in the study of Cas A. In April 2023, Webb’s MIRI (Mid-Infrared Instrument) started this chapter, revealing new and unexpected features within the inner shell of the supernova remnant. Many of those features are invisible in the new NIRCam image, and astronomers are investigating why.
‘Like Shards of Glass’
Infrared light is invisible to our eyes, so image processors and scientists translate these wavelengths of light to visible colors. In this newest image of Cas A, colors were assigned to different filters from NIRCam, and each of those colors hints at different activity occurring within the object.
At first glance, the NIRCam image may appear less colorful than the MIRI image. However, this simply comes down to the wavelengths in which the material from the object is emitting its light.
The most noticeable colors in Webb’s newest image are clumps represented in bright orange and light pink that make up the inner shell of the supernova remnant. Webb’s razor-sharp view can detect the tiniest knots of gas, comprised of sulfur, oxygen, argon, and neon from the star itself. Embedded in this gas is a mixture of dust and molecules, which will eventually become components of new stars and planetary systems. Some filaments of debris are too tiny to be resolved by even Webb, meaning they are comparable to or less than 10 billion miles across (around 100 astronomical units). In comparison, the entirety of Cas A spans 10 light-years across, or 60 trillion miles.
“With NIRCam’s resolution, we can now see how the dying star absolutely shattered when it exploded, leaving filaments akin to tiny shards of glass behind,” said Danny Milisavljevic of Purdue University, who leads the research team. “It’s really unbelievable after all these years studying Cas A to now resolve those details, which are providing us with transformational insight into how this star exploded.”
Hidden Green Monster
When comparing Webb’s new near-infrared view of Cas A with the mid-infrared view, its inner cavity and outermost shell are curiously devoid of color.
The outskirts of the main inner shell, which appeared as a deep orange and red in the MIRI image, now look like smoke from a campfire. This marks where the supernova blast wave is ramming into surrounding circumstellar material. The dust in the circumstellar material is too cool to be detected directly at near-infrared wavelengths, but lights up in the mid-infrared.
Researchers say the white color is light from synchrotron radiation, which is emitted across the electromagnetic spectrum, including the near-infrared. It’s generated by charged particles traveling at extremely high speeds spiraling around magnetic field lines. Synchrotron radiation is also visible in the bubble-like shells in the lower half of the inner cavity.
Also not seen in the near-infrared view is the loop of green light in the central cavity of Cas A that glowed in mid-infrared, nicknamed the Green Monster by the research team. This feature was described as “challenging to understand” by researchers at the time of their first look.
While the ‘green’ of the Green Monster is not visible in NIRCam, what’s left over in the near-infrared in that region can provide insight into the mysterious feature. The circular holes visible in the MIRI image are faintly outlined in white and purple emission in the NIRCam image – this represents ionized gas. Researchers believe this is due to the supernova debris pushing through and sculpting gas left behind by the star before it exploded.
Cassiopeia A NIRCam/MIRI (IMAGE)
This image provides a side-by-side comparison of supernova remnant Cassiopeia A (Cas A) as captured by NASA’s James Webb Space Telescope’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument). Objects in space reveal different aspects of their composition and behavior at different wavelengths. The outskirts of Cas A’s main inner shell, which appeared as a deep orange and red in the MIRI image, look like smoke from a campfire in the NIRCam image. The dust in the circumstellar material being slammed into by the shockwave is too cool to be detected directly at near-infrared wavelengths, but lights up in the mid-infrared. Also not seen in the near-infrared view is the loop of green light in the central cavity of Cas A that glows in mid-infrared, nicknamed the Green Monster by the research team.
CREDIT
NASA, ESA, CSA, STScI, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (University of Gent)
Baby Cas A
Researchers were also absolutely stunned by one fascinating feature at the bottom right corner of NIRCam’s field of view. They’re calling that large, striated blob Baby Cas A – because it appears like an offspring of the main supernova.
This is a light echo, where light from the star’s long-ago explosion has reached and is warming distant dust, which is glowing as it cools down. The intricacy of the dust pattern, and Baby Cas A’s apparent proximity to Cas A itself, are particularly intriguing to researchers. In actuality, Baby Cas A is located about 170 light-years behind the supernova remnant.
There are also several other, smaller light echoes scattered throughout Webb’s new portrait.
The Cas A supernova remnant is located 11,000 light-years away in the constellation Cassiopeia. It’s estimated to have exploded about 340 years ago from our point of view.
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
14-inch spacecraft delivers new details
about ‘hot Jupiters'
A spacecraft the size of a cereal box has collected precise measurements of the atmospheres of large and puffy planets called “hot Jupiters.” The findings, led by a team from the University of Colorado Boulder, could help reveal how the atmospheres around these and a host of other worlds are escaping into space.
The observations are the first results to come from a hard-working NASA spacecraft known as the Colorado Ultraviolet Transit Experiment (CUTE).
Kevin France, principal investigator for the mission, will present the group’s results at a media availability Monday, Dec. 11 at 4:30 p.m. at the 2023 meeting of the American Geophysical Union in San Francisco.
The diminutive spacecraft, which measures just 14 inches in length, may be cute, but its scientific findings are anything but. Since its launch in September 2021, CUTE has trained its single ultraviolet telescope at a series of hot Jupiters, some hundreds of light-years from Earth.
Hot Jupiters are among the hottest and angriest planets in the galaxy. As their name suggests, they are gas giants like our own Jupiter. These planets, however, hug much closer to their home stars, completing an orbit roughly once every several Earth days. In the process, stellar radiation cooks hot Jupiters to thousands of degrees Fahrenheit, and their atmospheres swell to enormous sizes, a bit like bread rising in an oven.
Researchers have long suspected that this constant pummeling from stellar radiation could strip away the atmospheres from around some exoplanets over millions-to-billions of years. Data from CUTE suggest that the process might not be so simple.
The CUTE team, which includes several undergraduate and graduate students, has observed seven hot Jupiters so far, with more on the way. Some of them seem to be losing their atmospheres, but others aren’t.
“The planets seem to be coming in all of the flavors,” said France, associate professor in the Laboratory for Atmospheric and Space Physics (LASP) and Department of Astrophysical and Planetary Sciences.
He added that CUTE is helping scientists to build out their field guide to the many kinds of planets that exist in the Milky Way Galaxy—including those that look nothing like Earth’s close neighbors.
“We want to understand how our solar system fits into the family of solar systems in the universe,” France said. “That means understanding the big planets, the small planets, the ones that have life and the ones that definitely don’t—and all of the important physical processes that are operating on these planets.”
Getting hot in here
CUTE’s road to scientific success wasn’t easy.
When the spacecraft first entered into orbit around Earth, France and his colleagues quickly noticed that it seemed to be experiencing a few glitches—a normal problem for many small satellites, or CubeSats, which often test out technology that’s never before flown into space. In one case, the shutter that protected CUTE’s telescope kept snapping shut when it wasn’t supposed to.
The team, which included several undergraduate and graduate students, didn’t give up. The researchers commanded the spacecraft to open its shutter, then drained the battery that fed it, preventing the apparatus from shutting again.
“CUTE is still working and collecting data today,” France said. “When we got our first real science results, it was really exciting.”
CUTE observes distant planets as they pass in front of their home stars, causing ultraviolet light from those stars to dim in the process. In some cases, the spacecraft is so precise that it can detect when starlight dims by just 1%.
In a paper published in September, the researchers described their observations of a world called WASP-189b. This planet orbits a star in the constellation Libra more than 300 light-years, or thousands of trillions of miles, from Earth. It’s also incredibly toasty, with its atmosphere reaching temperatures of roughly 15,000 degrees Fahrenheit, according to the team’s results. That’s thousands of degrees hotter than the surface of the sun.
CUTE’s observations also suggest that gas is escaping from around WASP-189b at a similarly staggering rate of about 400 million kilograms (nearly 900 million pounds) per second.
Planets evolving
Not all of the planets CUTE has studied in its first two years were so exciting. In unpublished results, the team observed a second planet called MASCARA-4b that didn’t seem to be losing much gas at all. Others, like KELT-9b, fell somewhere in the middle.
France and his colleagues hope that their results could help uncover why some planets lose big chunks of their atmosphere, while others remain mostly unchanged. He suspects that it has to do with a combination of the planets themselves (larger planets generate a stronger gravitational pull) and the dynamics of their stars (more active stars likely wreak more havoc on planets than sedate stars).
Those same processes potentially sculpt planets, both in and out of Earth’s solar system, over time. Scientists, for example, theorize that Mars once hosted a much thicker atmosphere, but the sun eroded it away over billions of years.
Atmospheric escape may also explain the origin of a class of planets known as “super Earths,” which are slightly larger than our own world.
“There’s a lot of evidence that suggests that super Earths begin as planets the size of Neptune with large, puffy atmospheres, which then lose so much mass that all that is left is the rocky core and possibly a thin atmosphere,” France said.
CUTE’s greatest legacy may be its impact on students, he said. The mission’s small team of about 20 people were involved in almost every aspect of the spacecraft’s life—from building the satellite to launching it, sending it commands, then downloading and analyzing scientific data. CUTE is currently orbiting about 326 miles (525 kilometers) above Earth’s surface, and is expected to reenter the atmosphere by 2027.
“All of these things are what happens on big NASA missions, just on a much larger scale,” France said. “Our students and early career scientists are getting the full experience from the proposal stage all the way to getting out the science product.”
NASA: some icy exoplanets may have habitable oceans and geysers
Peer-Reviewed PublicationIMAGE:
NASA’S CASSINI SPACECRAFT CAPTURED THIS IMAGE OF ENCELADUS ON NOV. 30, 2010. THE SHADOW OF THE BODY OF ENCELADUS ON THE LOWER PORTIONS OF THE JETS IS CLEARLY VISIBLE.
view moreCREDIT: NASA/JPL-CALTECH/SPACE SCIENCE INSTITUTE
A NASA study expands the search for life beyond our solar system by indicating that 17 exoplanets (worlds outside our solar system) could have oceans of liquid water, an essential ingredient for life, beneath icy shells. Water from these oceans could occasionally erupt through the ice crust as geysers. The science team calculated the amount of geyser activity on these exoplanets, the first time these estimates have been made. They identified two exoplanets sufficiently close where signs of these eruptions could be observed with telescopes.
The search for life elsewhere in the Universe typically focuses on exoplanets that are in a star’s “habitable zone,” a distance where temperatures allow liquid water to persist on their surfaces. However, it’s possible for an exoplanet that’s too distant and cold to still have an ocean underneath an ice crust if it has enough internal heating. Such is the case in our solar system where Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, have subsurface oceans because they are heated by tides from the gravitational pull of the host planet and neighboring moons.
These subsurface oceans could harbor life if they have other necessities, such as an energy supply as well as elements and compounds used in biological molecules. On Earth, entire ecosystems thrive in complete darkness at the bottom of oceans near hydrothermal vents, which provide energy and nutrients.
“Our analyses predict that these 17 worlds may have ice-covered surfaces but receive enough internal heating from the decay of radioactive elements and tidal forces from their host stars to maintain internal oceans,” said Dr. Lynnae Quick of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Thanks to the amount of internal heating they experience, all planets in our study could also exhibit cryovolcanic eruptions in the form of geyser-like plumes.” Quick is lead author of a paper on the research published on October 4 in the Astrophysical Journal.
The team considered conditions on 17 confirmed exoplanets that are roughly Earth-sized but less dense, suggesting that they could have substantial amounts of ice and water instead of denser rock. Although the planets’ exact compositions remain unknown, initial estimates of their surface temperatures from previous studies all indicate that they are much colder than Earth, suggesting that their surfaces could be covered in ice.
The study improved estimates of each exoplanet’s surface temperature by recalculating using the known surface brightness and other properties of Europa and Enceladus as models. The team also estimated the total internal heating in these exoplanets by using the shape of each exoplanet’s orbit to get the heat generated from tides and adding it to the heat expected from radioactive activity. Surface temperature and total heating estimates gave the ice layer thickness for each exoplanet since the oceans cool and freeze at the surface while being heated from the interior. Finally, they compared these figures to Europa’s and used estimated levels of geyser activity on Europa as a conservative baseline to estimate geyser activity on the exoplanets.
They predict that surface temperatures are colder than previous estimates by up to 60 degrees Fahrenheit (16 degrees Celsius). Estimated ice shell thickness ranged from about 190 feet (58 meters) for Proxima Centauri b and one mile (1.6 kilometers) for LHS 1140 b to 24 miles (38.6 kilometers) for MOA 2007 BLG 192Lb, compared to Europa’s estimated average of 18 miles (almost 29 kilometers). Estimated geyser activity went from just 17.6 pounds per second (about 8 kilograms/second) for Kepler 441b to 639,640 pounds/second (290,000 kilograms/second) for LHS 1140b and 13.2 million pounds/second (six million kilograms/second) for Proxima Centauri b, compared to Europa at 4,400 pounds/second (2,000 kilograms/second).
“Since our models predict that oceans could be found relatively close to the surfaces of Proxima Centauri b and LHS 1140 b, and their rate of geyser activity could exceed Europa's by hundreds to thousands of times, telescopes are most likely to detect geological activity on these planets,” said Quick, who is presenting this research December 12 at the American Geophysical Union meeting in San Francisco, California.
This activity could be seen when the exoplanet passes in front of its star. Certain colors of starlight could be dimmed or blocked by water vapor from the geysers. “Sporadic detections of water vapor in which the amount of water vapor detected varies with time, would suggest the presence of cryovolcanic eruptions,” said Quick. The water might contain other elements and compounds that could reveal if it can support life. Since elements and compounds absorb light at specific “signature” colors, analysis of the starlight would let scientists determine the geyser’s composition and evaluate the exoplanet’s habitability potential.
For planets like Proxima Centauri b that don’t cross their stars from our vantage point, geyser activity could be detected by powerful telescopes that are able to measure light that the exoplanet reflects while orbiting its star. Geysers would expel icy particles at the exoplanet’s surface which would cause the exoplanet to appear very bright and reflective.
The research was funded by NASA’s Habitable Worlds Program, the University of Washington's Astrobiology Program, and the Virtual Planetary Laboratory, a member of the NASA Nexus for Exoplanet System Science coordination group.
JOURNAL
The Astrophysical Journal
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Prospects for Cryovolcanic Activity on Cold Ocean Planets
