NASA's Chandra Reveals Star's Inner Conflict Before Explosion

X-ray Image of Cassiopeia A
Credit: X-ray: NASA/CXC/Meiji Univ./T. Sato et al.; Image Processing: NASA/CXC/SAO/N. Wolk

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A Tour of Cassiopeia A - More Videos

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This graphic features data from NASA’s Chandra X-ray Observatory of the Cassiopeia A (Cas A) supernova remnant, a frequent target of the telescope for more than a quarter century. New Chandra data continues to reveal fresh insight into this debris field from an exploded star. In the latest result, astronomers have now used Chandra to learn that the star’s interior violently rearranged itself mere hours before it exploded, as outlined in our press release. This discovery helps scientists better understand how massive stars explode and what happens to their remains afterward.

The main panel of this graphic is Chandra data that has been selected to show the location of different elements in the remains of the explosion: silicon (red), sulfur (yellow), calcium (green) and iron (purple). The blue color reveals the highest-energy X-ray emission detected by Chandra in Cas A, with the blue outer ring highlighting the expanding blast wave from the original explosion hundreds of years ago.

The inset to the upper left zooms in a smaller region of Cas A. This reveals data collected by Chandra that picks up relative amounts of silicon and neon. Areas with large amounts of silicon but smaller amounts of neon are labeled as Silicon-rich and Neon-poor, respectively, and are colored red. Alternatively, areas where Chandra detects the opposite — large amounts of neon but smaller amounts of silicon (Neon-rich and Silicon-poor) — are blue.

Cassiopeia A: A labeled version of the main image showing the relative abundances of silicon and neon in the inset. Credit: X-ray: NASA/CXC/Meiji Univ./T. Sato et al.; Image Processing: NASA/CXC/SAO/N. Wolk

These different regions provide crucial information about the supernova's progenitor, the star that exploded to form Cas A. They give evidence that just a few hours before it exploded, the progenitor's onion-like layers of elements in its interior were disrupted. The researchers think that part of an inner layer with large amounts of silicon traveled outwards and broke into a neighboring layer with lots of neon. This upheaval not only caused material rich in silicon to travel outwards, it also forced material rich in neon to travel inwards. Clear traces of these outward silicon flows and inward neon flows in Cas A are shown in the inset image, corresponding to the Silicon-rich and Neon-poor regions, and the Neon-rich and Silicon-poor regions, respectively.

Cassiopeia A: Schematic Illustration

This illustrated figure shows a cross-section of a massive star similar to the one that created the Cas A supernova remnant. The onion-like layers are dominated by heavier and heavier elements, beginning with hydrogen, and extending to helium, carbon, oxygen, silicon and iron in the center of the star. The cross-section is shown a few hours before the star's explosion as a supernova. Silicon-rich material made in nuclear reactions involving oxygen (in the narrow "O-burning shell"), are buoyant and push outwards in silicon-rich plumes, forcing neon-rich material further out to flow inwards. The motion of these silicon-rich and neon-rich materials disrupt the narrow shell where carbon and neon are undergoing nuclear reactions (the narrow "C-/Ne-burning shell"). Credit: NASA/CXC/Meiji Univ./T. Sato et al.

Because Chandra observes the elements are not smoothly mixed in the remnant now, it suggests there was not complete mixing of the silicon and neon with other elements immediately before or after the explosion.

These results have been published in the latest issue of The Astrophysical Journal and are available online. The authors of the study are Toshiki Sato (Meiji University in Japan), Kai Matsunga (Kyoto University in Japan), Hiroyuki Uchida (Kyoto), Satoru Katsuda (Saitama University in Japan), Koh Takahashi (National Astronomical Observatory of Japan), Hideyuki Umeda (University of Toyko in Japan), Tomoya Takiwaki (NAOJ), Ryo Sawada (University of Toyko), Takashi Yoshida (Kyoto), Ko Nakamura (Fukuoka University in Japan), Yui Kuboike (Meiji), Paul Plucinsky (Center for Astrophysics | Harvard & Smithsonian), and Jack Hughes (Rutgers University).

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

Quick Look: NASA's Chandra Reveals Star's Inner Conflict Before Explosion

Source: NASA’s Chandra X-ray Observatory

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Visual Description:

This release features a composite image of Cassiopeia A, a donut-shaped supernova remnant located about 11,000 light-years from Earth. Included in the image is an inset closeup, which highlights a region with relative abundances of silicon and neon.

Over three hundred years ago, Cassiopeia A, or Cas A, was a star on the brink of self-destruction. In composition it resembled an onion with layers rich in different elements such as hydrogen, helium, carbon, silicon, sulfur, calcium, and neon, wrapped around an iron core. When that iron core grew beyond a certain mass, the star could no longer support its own weight. The outer layers fell into the collapsing core, then rebounded as a supernova. This explosion created the donut-like shape shown in the composite image. The shape is somewhat irregular, with the thinner quadrant of the donut to the upper left of the off-center hole.

In the body of the donut, the remains of the star's elements create a mottled cloud of colors, marbled with red and blue veins. Here, sulfur is represented by yellow, calcium by green, and iron by purple. The red veins are silicon, and the blue veins, which also line the outer edge of the donut-shape, are the highest energy X-rays detected by Chandra and show the explosion's blast wave.

The inset uses a different color code and highlights a colorful, mottled region at the thinner, upper left quadrant of Cas A. Here, rich pockets of silicon and neon are identified in the red and blue veins, respectively. New evidence from Chandra indicates that in the hours before the star's collapse, part of a silicon-rich layer traveled outwards, and broke into a neighboring neon-rich layer. This violent breakdown of layers created strong turbulent flows and may have promoted the development of the supernova's blast wave, facilitating the star's explosion. Additionally, upheaval in the interior of the star may have produced a lopsided explosion, resulting in the irregular shape, with an off-center hole (and a thinner bite of donut!) at our upper left.

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Fast Facts for Cassiopeia A:

Scale: Image is about 12.2 arcmin (39 light-years) across.
Category: Supernovas & Supernova Remnants
Coordinates (J2000): RA 23h 23m 26.7s | Dec +58° 49´ 03.00"
Constellation: Cassiopeia
Observation Dates: Nine observations in 2004: Feb 8, Apr 14, 18, 20, 22, 25 28, May 01, 05
Observation Time: 278 hours (11 days 14 hours)
Obs. ID: 4634-4639, 5196, 5319-5320
Instrument: ACIS
Also Known As: Cas A
References: Sato, T. et al, 2025, Accepted; arXiv:2507.07563.
Color Code: X-ray: red, green, blue; Inset: red, white, blue
Distance Estimate: About 11,000 light-years

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The Explosion's Aftermath: Cosmic Rays from the Remnant of a Supernova

The Cassiopeia A supernova remnant as seen in X-rays during its original observation, with low-energy X-rays detected by Chandra in red, yellow, and green, and high-energy X-rays detected by NuSTAR in blue. Credit: NASA/JPL-Caltech/CXC/SAO. Download Image

A gigantic explosion may be the end of a massive star's life, but it is by no means the end of its story. Take Cassiopeia A (Cas A for short), the remnants of the most recent known core-collapse supernova in our Galaxy—a stellar explosion about 11,000 light-years away that would have been visible to Earth around 350 years ago. Since then, debris from the explosion has been blasting into the universe as fast-moving material plows into its slow-moving surroundings and creates powerful shockwaves.

These shockwaves heat the gas to millions of degrees, causing it to glow brightly in optical, ultraviolet, and even X-ray light. These shocks can also accelerate particles like electrons to nearly the speed of light, becoming what are known as cosmic rays. These high-energy cosmic rays also emit X-rays, which carry information about the heating and cooling processes happening within the remnant.

Low-energy X-ray observations taken by NASA’s Chandra X-ray Observatory over the past two decades have shown that the Cas A supernova remnant is expanding and slowly cooling down. However, since low-energy X-rays are produced by both hot gas and high-energy cosmic rays, it is difficult to determine which of these light sources contribute the most to these changes.

That's where NASA’s NuSTAR satellite comes in. With its ability to detect the high-energy X-rays that are only produced by the high-energy cosmic rays, NuSTAR can produce maps of the most energetic regions of the supernova remnant and watch how these regions evolve over time.

In a recent paper led by Dr Jooyun Woo, then a graduate student at Columbia University, astronomers used new NuSTAR observations of Cas A and compared them with observations taken ten years ago. If the electrons had been accelerated all at once in the initial shock wave, then we would have expected them to have cooled down and become dimmer. In comparing the two images, Woo and her co-authors found that the X-ray brightness of these shock regions did not decrease as much as expected. This tells us that cosmic ray heating is still taking place, keeping the supernova remnant bright in the latest NuSTAR image. Studying such changes in brightness over time allows astronomers to compare different models of electron acceleration, enabling the remnants of the relatively nearby and recent Cas A supernova to act as a laboratory in which we can test physical theories in environments that we can't reproduce in labs on Earth.

Even with its slower-than-expected rate of dimming, one day Cas A will fade away and become too faint for a telescope like NuSTAR to detect, possibly within a century. It is incredible to think of how many advances in astronomy have taken place over the last 350 years to allow us to see the high-energy emission from this explosion before it vanishes!

Source: NASA's Nuclear Spectroscopic Telescope Array (NuSTAR)/News

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NASA's Webb Reveals Intricate Layers of Interstellar Dust, Gas

Cassiopeia A Light Echoes (NIRCam Images)
Credits/Image: NASA, ESA, CSA, STScI, Jacob Jencson (Caltech/IPAC)

Cassiopeia A Light Echoes (Spitzer Context)
Credits/Image: NASA, ESA, CSA, STScI

Individual Image Credits: 1. Spitzer Image: NASA/JPL-Caltech/Y. Kim (Univ. of Arizona/Univ. of Chicago); 2. Cassiopeia A Inset: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (Ghent University), Tea Temim (Princeton University); 3. Light Echoes Inset: NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC)

Cassiopeia A Light Echoes (Compass Image)
Credits/Image: NASA, ESA, CSA, STScI, Jacob Jencson (Caltech/IPAC)

Cassiopeia A Light Echoes Time-lapse
Credits/Video: NASA, ESA, CSA, STScI, Jacob Jencson (Caltech/IPAC), Joseph DePasquale (STScI)

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Once upon a time, the core of a massive star collapsed, creating a shockwave that blasted outward, ripping the star apart as it went. When the shockwave reached the star’s surface, it punched through, generating a brief, intense pulse of X-rays and ultraviolet light that traveled outward into the surrounding space. About 350 years later, that pulse of light has reached interstellar material, illuminating it, warming it, and causing it to glow in infrared light.

NASA’s James Webb Space Telescope has observed that infrared glow, revealing fine details resembling the knots and whorls of wood grain. These observations are allowing astronomers to map the true 3D structure of this interstellar dust and gas (known as the interstellar medium) for the first time.

“We were pretty shocked to see this level of detail,” said Jacob Jencson of Caltech/IPAC in Pasadena, principal investigator of the science program.

“We see layers like an onion,” added Josh Peek of the Space Telescope Science Institute in Baltimore, a member of the science team. “We think every dense, dusty region that we see, and most of the ones we don’t see, look like this on the inside. We just have never been able to look inside them before.”

The team is presenting their findings in a press conference at the 245th meeting of the American Astronomical Society in National Harbor, Maryland.

“Even as a star dies, its light endures—echoing across the cosmos. It’s been an extraordinary three years since we launched NASA’s James Webb Space Telescope. Every image, every discovery, shows a portrait not only of the majesty of the universe but the power of the NASA team and the promise of international partnerships. This groundbreaking mission, NASA’s largest international space science collaboration, is a true testament to NASA’s ingenuity, teamwork, and pursuit of excellence,” said NASA Administrator Bill Nelson. “What a privilege it has been to oversee this monumental effort, shaped by the tireless dedication of thousands of scientists and engineers around the globe. This latest image beautifully captures the lasting legacy of Webb—a keyhole into the past and a mission that will inspire generations to come.”

Taking a CT Scan

The images from Webb’s NIRCam (Near-Infrared Camera) highlight a phenomenon known as a light echo. A light echo is created when a star explodes or erupts, flashing light into surrounding clumps of dust and causing them to shine in an ever-expanding pattern. Light echoes at visible wavelengths (such as those seen around the star V838 Monocerotis ) are due to light reflecting off of interstellar material. In contrast, light echoes at infrared wavelengths are caused when the dust is warmed by energetic radiation and then glows.

The researchers targeted a light echo that had previously been observed by NASA’s retired Spitzer Space Telescope. It is one of dozens of light echoes seen near the Cassiopeia A supernova remnant – the remains of the star that exploded. The light echo is coming from unrelated material that is behind Cassiopeia A, not material that was ejected when the star exploded.

The most obvious features in the Webb images are tightly packed sheets. These filaments show structures on remarkably small scales of about 400 astronomical units, or less than one-hundredth of a light-year. (An astronomical unit, or AU, is the average Earth-Sun distance. Neptune’s orbit is 60 AU in diameter.)

“We did not know that the interstellar medium had structures on that small of a scale, let alone that it was sheet-like,” said Peek.

These sheet-like structures may be influenced by interstellar magnetic fields. The images also show dense, tightly wound regions that resemble knots in wood grain. These may represent magnetic “islands” embedded within the more streamlined magnetic fields that suffuse the interstellar medium.

“This is the astronomical equivalent of a medical CT scan,” explained Armin Rest of the Space Telescope Science Institute, a member of the science team. “We have three slices taken at three different times, which will allow us to study the true 3D structure. It will completely change the way we study the interstellar medium.”

Future Work

The team’s science program also includes spectroscopic observations using Webb’s MIRI (Mid-Infrared Instrument). They plan to target the light echo multiple times, weeks or months apart, to observe how it evolves as the light echo passes by.

“We can observe the same patch of dust before, during, and after it’s illuminated by the echo and try to look for any changes in the compositions or states of the molecules, including whether some molecules or even the smallest dust grains are destroyed,” said Jencson.

Infrared light echoes are also extremely rare, since they require a specific type of supernova explosion with a short pulse of energetic radiation. NASA’s upcoming Nancy Grace Roman Space Telescope will conduct a survey of the galactic plane that may find evidence of additional infrared light echoes for Webb to study in detail.

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 CSA (Canadian Space Agency).

Source: NASA's James Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Jacob Jencson (Caltech/IPAC

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

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Investigating the Origins of the Crab Nebula With NASA's Webb

Crab Nebula
Credits: Image: NASA, ESA, CSA, STScI, Tea Temim (Princeton University)

Images | Videos

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A team of scientists used NASA’s James Webb Space Telescope to parse the composition of the Crab Nebula, a supernova remnant located 6,500 light-years away in the constellation Taurus. With the telescope’s MIRI (Mid-Infared Instrument) and NIRCam (Near-Infrared Camera), the team gathered data that is helping to clarify the Crab Nebula’s history.

The Crab Nebula is the result of a core-collapse supernova from the death of a massive star. The supernova explosion itself was seen on Earth in 1054 CE and was bright enough to view during the daytime. The much fainter remnant observed today is an expanding shell of gas and dust, and outflowing wind powered by a pulsar, a rapidly spinning and highly magnetized neutron star.

The Crab Nebula is also highly unusual. Its atypical composition and very low explosion energy previously have been explained by an electron-capture supernova — a rare type of explosion that arises from a star with a less-evolved core made of oxygen, neon, and magnesium, rather than a more typical iron core.

“Now the Webb data widen the possible interpretations,” said Tea Temim, lead author of the study at Princeton University in New Jersey. “The composition of the gas no longer requires an electron-capture explosion, but could also be explained by a weak iron core-collapse supernova.”

Studying the Present to Understand the Past

Past research efforts have calculated the total kinetic energy of the explosion based on the quantity and velocities of the present-day ejecta. Astronomers deduced that the nature of the explosion was one of relatively low energy (less than one-tenth that of a normal supernova), and the progenitor star’s mass was in the range of eight to 10 solar masses — teetering on the thin line between stars that experience a violent supernova death and those that do not.

However, inconsistencies exist between the electron-capture supernova theory and observations of the Crab, particularly the observed rapid motion of the pulsar. In recent years, astronomers have also improved their understanding of iron core-collapse supernovae and now think that this type can also produce low-energy explosions, providing that the stellar mass is adequately low.

Webb Measurements Reconcile Historic Results

To lower the level of uncertainty surrounding the Crab’s progenitor star and nature of the explosion, the team led by Temim used Webb’s spectroscopic capabilities to hone in on two areas located within the Crab’s inner filaments.

Theories predict that because of the different chemical composition of the core in an electron-capture supernova, the nickel to iron (Ni/Fe) abundance ratio should be much higher than the ratio measured in our Sun (which contains these elements from previous generations of stars). Studies in the late 1980s and early 1990s measured the Ni/Fe ratio within the Crab using optical and near-infrared data and noted a high Ni/Fe abundance ratio that seemed to favor the electron-capture supernova scenario.

The Webb telescope, with its sensitive infrared capabilities, is now advancing Crab Nebula research. The team used MIRI’s spectroscopic abilities to measure the nickel and iron emission lines, resulting in a more reliable estimate of the Ni/Fe abundance ratio. They found that the ratio was still elevated compared to the Sun, but only modestly and much lower in comparison to prior estimates.

The revised values are consistent with electron-capture, but do not rule out an iron core-collapse explosion from a similarly low-mass star. (Higher-energy explosions from higher-mass stars are expected to produce ratios closer to solar abundances.) Further observational and theoretical work will be needed to distinguish between these two possibilities.

“At present, the spectral data from Webb covers two small regions of the Crab, so it’s important to study much more of the remnant and identify any spatial variations,” said Martin Laming of the Naval Research Laboratory in Washington and a co-author of the paper. “It would be interesting to see if we could identify emission lines from other elements, like cobalt or germanium.”

Mapping the Crab’s Current State

Besides pulling spectral data from two small regions of the Crab Nebula’s interior to measure the abundance ratio, the telescope also observed the remnant’s broader environment to understand details of the synchrotron emission and the dust distribution.

The images and data collected by MIRI enabled the team to isolate the dust emission within the Crab and map it in high resolution for the first time. By mapping the warm dust emission with Webb, and even combining it with the Herschel Space Observatory’s data on cooler dust grains, the team created a well-rounded picture of the dust distribution: The outermost filaments contain relatively warmer dust, while cooler grains are prevalent near the center.

“Where dust is seen in the Crab is interesting because it differs from other supernova remnants, like Cassiopeia A and Supernova 1987A," said Nathan Smith of the Steward Observatory at the University of Arizona and a co-author of the paper. “In those objects, the dust is in the very center. In the Crab, the dust is found in the dense filaments of the outer shell. The Crab Nebula lives up to a tradition in astronomy: The nearest, brightest, and best-studied objects tend to be bizarre.”

These findings have been accepted for publication in The Astrophysical Journal Letters.

The observations were taken as part of General Observer program 1714.

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 CSA (Canadian Space Agency).

Source: NASA's James Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Abigail Major
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Tea Temim (Princeton University)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

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Cassiopeia A: NASA Telescopes Chase Down "Green Monster" in Star's Debris

Cassiopeia A
Credit: X-ray: NASA/CXC/SAO; Optical: NASA/ESA/STScI;
IR: NASA/ESA/CSA/STScI/Milisavljevic et al., NASA/JPL/CalTech;
Image Processing: NASA/CXC/SAO/J. Schmidt and K. Arcand

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Tour: New Stellar Danger to Planets Identified by NASA's Chandra (Video YouTube)

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For the first time astronomers have combined data from NASA’s Chandra X-ray Observatory and James Webb Space Telescope to study the well-known supernova remnant Cassiopeia A (Cas A). As described in our latest press release, this work has helped explain an unusual structure in the debris from the destroyed star called the “Green Monster”, first discovered in Webb data in April 2023. The research has also uncovered new details about the explosion that created Cas A about 340 years ago, from Earth’s perspective.

A new composite image contains X-rays from Chandra (blue), infrared data from Webb (red, green, blue), and optical data from Hubble (red and white). The outer parts of the image also include infrared data from NASA’s Spitzer Space Telescope (red, green and blue). The outline of the Green Monster can be seen by mousing over the image.

The Chandra data reveals hot gas, mostly from supernova debris from the destroyed star, including elements like silicon and iron. In the outer parts of Cas A the expanding blast wave is striking surrounding gas that was ejected by the star before the explosion. The X-rays are produced by energetic electrons spiraling around magnetic field lines in the blast wave. These electrons light up as thin arcs in the outer regions of Cas A, and in parts of the interior. Webb highlights infrared emission from dust that is warmed up because it is embedded in the hot gas seen by Chandra, and from much cooler supernova debris. The Hubble data shows stars in the field.

A separate graphic shows a color Chandra image, where red shows iron and magnesium at low X-ray energies, green shows silicon at intermediate X-ray energies and blue shows the highest energy X-rays, from electrons spiraling around magnetic field lines. An outline of the Green Monster, plus the locations of the blast wave, and of debris rich in silicon and iron are labeled.

Chandra Image of Cassiopeia A, Labeled
Credit: X-ray: NASA/CXC/SAO

Detailed analysis by the researchers found that filaments in the outer part of Cas A, from the blast wave, closely matched the X-ray properties of the Green Monster, including less iron and silicon than in the supernova debris. This interpretation is apparent from the color Chandra image, which shows that the colors inside the Green Monster’s outline best match with the colors of the blast wave rather than the debris with iron and silicon. The authors conclude that the Green Monster was created by a blast wave from the exploded star slamming into material surrounding it, supporting earlier suggestions from the Webb data alone.

The debris from the explosion is seen by Chandra because it is heated to tens of millions of degrees by shock waves, akin to sonic booms from a supersonic plane. Webb can see some material that has not been affected by shock waves, what can be called “pristine” debris.

To learn more about the supernova explosion, the team compared the Webb view of the pristine debris with X-ray maps of radioactive elements that were created in the supernova. They used NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) data to map radioactive titanium — still visible today — and Chandra to map where radioactive nickel was by measuring the locations of iron. Radioactive nickel decays to form iron. An additional image shows the iron-rich debris (tracing where radioactive nickel was located) in green, the radioactive titanium in blue and the pristine debris seen in orange and yellow.

Iron/Titanium/Pristine Debris Cassiopeia A, Labeled
Credit: X-ray: NASA/CXC/SAO; Image Processing: NASA/CXC/SAO/J. Schmidt and J. Major

Some filaments of pristine debris near the center of Cas A, seen with Webb, are connected to the iron seen with Chandra farther out. Radioactive titanium is seen where pristine debris is relatively weak. These comparisons suggest that radioactive material seen in X-rays has helped shape the pristine debris near the center of the remnant seen with Webb, forming cavities. The fine structures in the pristine debris were most likely formed when the star’s inner layers were violently mixed with hot, radioactive matter produced during collapse of the star’s core under gravity.

These results were presented by Dan Milisavljevic from Purdue University at the 243rd meeting of the American Astronomical Society in New Orleans. They are described in more detail in two papers submitted to Astrophysical Journal Letters, one led by Milisavljevic focused on the Webb results (preprint here) and the other led by Jacco Vink of the University of Amsterdam focused on the Chandra results (preprint here). The co-authors of Vink’s paper are Manan Agarwal (University of Amsterdam, the Netherlands), Patrick Slane (Center for Astrophysics | Harvard & Smithsonian - CfA), Ilse De Looze (Ghent University, Belgium), Dan Milisavljevic, Daniel Patnaude (CfA), Paul Plucinsky (CfA), and Tea Temin (Princeton University). Related papers by other members of the research team are also in preparation.

The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

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.

A Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington, NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp. in Dulles, Virginia. NuSTAR’s mission operations center is at the University of California, Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Science Archive Research Center at the agency’s Goddard Space Flight Center in Greenbelt, Maryland. ASI provides the mission’s ground station and a mirror data archive. Caltech manages JPL for NASA.

 

Quick Look: NASA Telescopes Chase Down "Green Monster" in Star's Debris

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Visual Description:

This image of Cassiopeia A resembles a disk of electric light with red clouds, glowing white streaks, red and orange flames, and an area near the center of the remnant resembling a somewhat circular region of green lightning. X-rays from Chandra are blue and reveal hot gas, mostly from supernova debris from the destroyed star, and include elements like silicon and iron. X-rays are also present as thin arcs in the outer regions of the remnant.

Infrared data from Webb is red, green, and blue. Webb highlights infrared emission from dust that is warmed up because it is embedded in the hot gas seen by Chandra, and from much cooler supernova debris. Hubble data shows a multitude of stars that permeate the field of view.

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Fast Facts for (Cassiopeia A):

Scale: Image is about 8 arcmin (25.5 light-years) across.
Category: Supernovas & Supernova Remnants
Coordinates (J2000): RA 23h 23m 26.7s | Dec +58° 49´ 03.00"
Constellation: Cassiopeia
Observation Dates: Nine observations in 2004: Feb 8, Apr 14, 18, 20, 22, 25 28, May 1, 5
Observation Time: 277 hours 58 minutes (11 days 13 hours 58 minutes)
Obs. ID: 4634-4639, 5196, 5319-5320
Instrument: ACIS
Also Known As: Cas A
References: Vink, J. et al. 2024, ApJ, submitted. Milisavljevic, D. et al. 2024, ApJ, submitted.
Color Code: X-ray: blue; Optical: red, white; Infrared: red, green, blue
Distance Estimate: About 11,000 light-years

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NASA's Webb Stuns With New High-Definition Look at Exploded Star

Cassiopeia A (NIRCam Image)

Credits: Image: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGent), Tea Temim (Princeton University)

Cassiopeia A Close-ups (NIRCam Image)

Credits: Image: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGent), Tea Temim (Princeton University)

Cassiopeia A (NIRCam and MIRI side by side)

Credits: Image: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGent), Tea Temim (Princeton University)

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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.

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.

Source: NASA's James Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Hannah Braun
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Danny Milisavljevic (Purdue University), Ilse De Looze (UGent), Tea Temim (Princeton University)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

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Webb Reveals Never-Before-Seen Details in Cassiopeia A

Cassiopeia A (MIRI Image)

< div style="text-align: justify;"> Credits: Image: NASA, ESA, CSA, Danny Milisavljevic (Purdue University), Tea Temim (Princeton University), Ilse De Looze (UGent). Image Processing: Joseph DePasquale (STScI)

Release Images

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The explosion of a star is a dramatic event, but the remains the star leaves behind can be even more dramatic. A new mid-infrared image from NASA’s 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. Cas A is the youngest known remnant from an exploding, massive star in our galaxy, which makes it a unique opportunity to learn more about how such supernovae occur.

“Cas A represents our best opportunity to look at the debris field of an exploded star and run a kind of stellar autopsy to understand what type of star was there beforehand and how that star exploded,” said Danny Milisavljevic of Purdue University in West Lafayette, Indiana, principal investigator of the Webb program that captured these observations.

“Compared to previous infrared images, we see incredible detail that we haven't been able to access before,” added Tea Temim of Princeton University in Princeton, New Jersey, a co-investigator on the program.

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

Dissecting the Image

The striking colors of the new Cas A image, in which infrared light is translated into visible-light wavelengths, hold a wealth of scientific information the team is just beginning to tease out. On the bubble’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 gas and dust.

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 due to a mix of various heavy elements, such as oxygen, argon, and neon, as well as dust emission.

“We’re still trying to disentangle all these sources of emission,” said Ilse De Looze of Ghent University in Belgium, another co-investigator on the program.

The stellar material can also be seen as fainter wisps near the cavity’s interior.

Perhaps most prominently, a loop represented in green extends across the right side of the central cavity. “We’ve nicknamed it the Green Monster in honor of Fenway Park in Boston. If you look closely, you’ll notice that it’s pockmarked with what look like mini-bubbles,” said Milisavljevic. “The shape and complexity are unexpected and challenging to understand.”

Origins of Cosmic Dust – and Us

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.

“In Cas A, we can spatially resolve regions that have different gas compositions and look at what types of dust were formed in those regions,” explained Temim.

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.

“By understanding the process of exploding stars, we’re reading our own origin story,” said Milisavljevic. “I’m going to spend the rest of my career trying to understand what’s in this data set.”

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

The James Webb Space Telescope is the world’s premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe 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.

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About This Release

Credits:

Media Contact:

Christine Pulliam

 Space Telescope Science Institute, Baltimore, Maryland

Permissions: Content Use Policy

Contact Us: Direct inquiries to theNews Team.

Source: NASA's James Webb Space Telescope/News

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Cassiopeia A: NASA's IXPE Helps Unlock the Secrets of Famous Exploded Star

Cassiopeia A
Credit: X-ray: Chandra: NASA/CXC/SAO, IXPE: NASA/MSFC/J. Vink et al.; Optical: NASA/STScI

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For the first time, astronomers have measured and mapped polarized X-rays from the remains of an exploded star, using NASA’s Imaging X-ray Polarimetry Explorer (IXPE). The findings, which come from observations of a stellar remnant called Cassiopeia A, shed new light on the nature of young supernova remnants, which accelerate particles close to the speed of light.

Launched on Dec. 9, 2021, IXPE, a collaboration between NASA and the Italian Space Agency, is the first satellite that can measure the polarization of X-ray light with this level of sensitivity and clarity.

All forms of light — from radio waves to gamma rays — can be polarized. Unlike the polarized sunglasses we use to cut the glare from sunlight bouncing off a wet road or windshield, IXPE’s detectors maps the tracks of incoming X-ray light. Scientists can use these individual track records to figure out the polarization, which tells the story of what the X-rays went through.

Cassiopeia A (Cas A for short) was the first object IXPE observed after it began collecting data. One of the reasons Cas A was selected is that its shock waves — like a sonic boom generated by a jet — are some of the fastest in the Milky Way. The shock waves were generated by the supernova explosion that destroyed a massive star after it collapsed. Light from the blast swept past Earth more than three hundred years ago.

“Without IXPE, we have been missing crucial information about objects like Cas A,” said Pat Slane at the Center for Astrophysics | Harvard & Smithsonian, who leads the IXPE investigations of supernova remnants. “This result is teaching us about a fundamental aspect of the debris from this exploded star — the behavior of its magnetic fields.”

Magnetic fields, which are invisible, push and pull on moving charged particles like protons and electrons. Closer to home, they are responsible for keeping magnets stuck to a kitchen fridge. Under extreme conditions, such as an exploded star, magnetic fields can boost these particles to near-light-speed.

Despite their super-fast speeds, particles swept up by shock waves in Cas A do not fly away from the supernova remnant because they are trapped by magnetic fields in the wake of the shocks. The particles are forced to spiral around the magnetic field lines, and the electrons give off an intense kind of light called “synchrotron radiation,” which is polarized.

By studying the polarization of this light, scientists can “reverse engineer” what’s happening inside Cas A at very small scales — details that are difficult or impossible to observe in other ways. The angle of polarization tells us about the direction of these magnetic fields. If the magnetic fields close to the shock fronts are very tangled, the chaotic mix of radiation from regions with different magnetic field directions will give off a smaller amount of polarization.

Previous studies of Cas A with radio telescopes have shown that the radio synchrotron radiation is produced in regions across almost the entire supernova remnant. Astronomers found that only a small amount of the radio waves were polarized — about 5%. They also determined that the magnetic field is oriented radially, like the spokes of a wheel, spreading out from near the center of the remnant towards the edge.

Data from NASA’s Chandra X-ray Observatory, on the other hand, show that the X-ray synchrotron radiation mainly comes from thin regions along the shocks, near the circular outer rim of the remnant, where the magnetic fields were predicted to align with the shocks. Chandra and IXPE use different kinds of detectors and have different levels of angular resolution, or sharpness. Launched in 1999, Chandra’s first science image was also of Cas A.

Before IXPE, scientists predicted X-ray polarization would be produced by magnetic fields that are perpendicular to magnetic fields observed by radio telescopes.

Instead, IXPE data show that the magnetic fields in X-rays tend to be aligned in radial directions even very close to the shock fronts. The X-rays also reveal a lower amount of polarization than radio observations showed, which suggests that the X-rays come from turbulent regions with a mix of many different magnetic field directions.

Cassiopeia A Polarization Vectors
Credit: Chandra: NASA/CXC/SAO; IXPE: NASA/MSFC

"These IXPE results were not what we expected, but as scientists we love being surprised,” says Dr. Jacco Vink of the University of Amsterdam and lead author of the paper describing the IXPE results on Cas A. “The fact that a smaller percentage of the X-ray light is polarized is a very interesting — and previously undetected — property of Cas A.”

The IXPE result for Cas A is whetting the appetite for more observations of supernova remnants that are currently underway. Scientists expect each new observed object will reveal new answers — and pose even more questions — about these important objects that seed the Universe with critical elements.

“This study enshrines all the novelties that IXPE brings to astrophysics,” said Dr. Riccardo Ferrazzoli with the Italian National Institute for Astrophysics/Institute for Space Astrophysics and Planetology in Rome. “Not only did we obtain information on X-ray polarization properties for the first time for these sources, but we also know how these change in different regions of the supernova. As the first target of the IXPE observation campaign, Cas A provided an astrophysical 'laboratory' to test all the techniques and analysis tools that the team has developed in recent years.”

“These results provide a unique view of the environment necessary to accelerate electrons to incredibly high energies," said co-author Dmitry Prokhorov, also of the University of Amsterdam. “We are just at the beginning of this detective story, but so far the IXPE data are providing new leads for us to track down.”

IXPE is a collaboration between NASA and the Italian Space Agency with partners and science collaborators in 12 countries. Ball Aerospace, headquartered in Broomfield, Colorado, manages spacecraft operations together with the University of Colorado's Laboratory for Atmospheric and Space sciences, which operates IXPE for NASA’s Marshall Space Flight Center in Huntsville, Alabama.

Source: NASA’s Chandra X-ray Observatory

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Fast Facts for Cassiopeia A:

Scale: Main image is about 8.91 arcmin (29 light-years) across.
Category: Supernovas & Supernova Remnants
Coordinates (J2000): RA 23h 23m 26.7s | Dec +58° 49' 03.00"
Constellation: Cassiopeia
Observation Date: 16 pointings between Jan 2000-Nov 2010
Observation Time: 353 hours (14 days, 17 hours)
Obs. ID: 114, 1952, 4634-4639, 5196, 5319, 5320, 6690, 10935, 10936, 12020, 13177
Instrument: ACIS
Also Known As: Cas A
References: Vink, J. et al., 2022, ApJ, 938, 40; arXiv:2206.06713
Color Code: X-ray: Chandra (blue/cyan), IXPE (turquoise); Optical: gold;
Distance Estimate: About 11,000 light-years

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NASA’s IXPE Sends First Science Image

This image of the supernova remnant Cassiopeia A combines some of the first X-ray data collected by NASA’s Imaging X-ray Polarimetry Explorer, shown in magenta, with high-energy X-ray data from NASA’s Chandra X-Ray Observatory, in blue. Credits: NASA/CXC/SAO/IXPE

This image from NASA’s Imaging X-ray Polarimetry Explorer maps the intensity of X-rays coming from the observatory’s first target, the supernova remnant Cassiopeia A. Colors ranging from cool purple and blue to red and hot white correspond with the increasing brightness of the X-rays. The image was created using X-ray data collected by IXPE between Jan. 11-18. Credits: NASA

In time for Valentine’s Day, NASA’s Imaging X-Ray Polarimetry Explorer which launched Dec. 9, 2021, has delivered its first imaging data since completing its month-long commissioning phase.

All instruments are functioning well aboard the observatory, which is on a quest to study some of the most mysterious and extreme objects in the universe.

IXPE first focused its X-ray eyes on Cassiopeia A, an object consisting of the remains of a star that exploded in the 17^th century. The shock waves from the explosion have swept up surrounding gas, heating it to high temperatures and accelerating cosmic ray particles to make a cloud that glows in X-ray light. Other telescopes have studied Cassiopeia A before, but IXPE will allow researchers to examine it in a new way.

In the image above, the saturation of the magenta color corresponds to the intensity of X-ray light observed by IXPE. It overlays high energy X-ray data, shown in blue, from NASA’s Chandra X-Ray Observatory. Chandra and IXPE, with different kinds of detectors, capture different levels of angular resolution, or sharpness. An additional version of this image is available showing only IXPE data. These images contain IXPE data collected from Jan. 11 to 18.

After Chandra launched in 1999, its first image was also of Cassiopeia A. Chandra’s X-ray imagery revealed, for the first time, that there is a compact object in the center of the supernova remnant, which may be a black hole or neutron star.

“The IXPE image of Cassiopeia A is as historic as the Chandra image of the same supernova remnant,” said Martin C. Weisskopf, the IXPE principal investigator based at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “It demonstrates IXPE’s potential to gain new, never-before-seen information about Cassiopeia A, which is under analysis right now.”

A key measurement that scientists will make with IXPE is called polarization, a way of looking at how X-ray light is oriented as it travels through space. The polarization of light contains clues to the environment where the light originated. IXPE’s instruments also measure the energy, the time of arrival, and the position in the sky of the X-rays from cosmic sources. 

“The IXPE image of Cassiopeia A is bellissima, and we look forward to analyzing the polarimetry data to learn even more about this supernova remnant,” said Paolo Soffitta, the Italian principal investigator for IXPE at the National Institute of Astrophysics (INAF) in Rome.

With polarization data from Cassiopeia A, IXPE will allow scientists to see, for the first time, how the amount of polarization varies across the supernova remnant, which is about 10 light-years in diameter. Researchers are currently working with the data to create the first-ever X-ray polarization map of the object. This will reveal new clues about how X-rays are produced at Cassiopeia A.

“IXPE's future polarization images should unveil the mechanisms at the heart of this famous cosmic accelerator,” said Roger Romani, an IXPE co-investigator at Stanford University. “To fill in some of those details, we’ve developed a way to make IXPE’s measurements even more precise using machine learning techniques. We’re looking forward to what we’ll find as we analyze all the data.”

IXPE launched on a Falcon 9 rocket from Cape Canaveral, and now orbits 370 miles (600 kilometers) above Earth’s equator. The mission is a collaboration between NASA and the Italian Space Agency with partners and science collaborators in 12 countries. Ball Aerospace, headquartered in Broomfield, Colorado, manages spacecraft operations.

https://www.nasa.gov/mission_pages/ixpe/index.html

 

Elizabeth Landau
NASA Headquarters
elizabeth.r.landau@nasa.gov
202-358-0845

Molly Porter
NASA's Marshall Space Flight Center
molly.a.porter@nasa.gov
256-424-5158

Source: NASA/Imaging X-Ray Polarimetry Explorer (IXPE)

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Smoking-gun evidence for neutrinos’ role in supernova explosions

Figure 1: The Cassiopeia A supernova remnant has iron-rich plumes that contain titanium and chromium (areas with thick yellow outlines on right). This observation provides support for a model in which neutrinos help drive supernova explosions. © 2021 NASA/CXC/RIKEN/T. Sato et al.; NuSTAR: NASA/NuSTAR

Supernova explosions are sustained by neutrinos from neutron stars, a new observation suggests

A model for supernova explosions first proposed in the 1980s has received strong support from the observation by RIKEN astrophysicists of titanium-rich plumes emanating from a remnant of such an explosion1.

Some supernova explosions are the death throes of stars that are at least eight times more massive than our Sun. They are one of the most cataclysmic events in the Universe, unleashing as much energy in a few seconds as the Sun will generate in 10 billion years.

In contrast, neutrinos are among the most ethereal of members of the elementary-particle zoo—they are at least 5 million times lighter than an electron and about 10 quadrillion of them flit through your body every second without interacting with it.

It’s hard to conceive that there could be any connection between supernovas and neutrinos, but a model advanced in the 1980s proposed that supernovas would not occur if it were not for the heating provided by neutrinos.

This type of supernova starts when the core of a massive star collapses into a neutron star—an incredibly dense star that is roughly 20 kilometers in diameter. The remainder of the star collapses under gravity, hits the neutron star, and rebounds off it, creating a shockwave.

However, many supernova models predict that this shockwave will fade before it can escape the star’s gravity. Factoring in heating generated by neutrinos ejected from the neutron star could provide the energy needed to sustain shockwaves and hence the supernova explosion.

Now, Shigehiro Nagataki at the RIKEN Astrophysical Big Bang Laboratory, Toshiki Sato, who was at the RIKEN Nishina Center for Accelerator-Based Science at the time of the study, and co-workers have found strong evidence supporting this model by detecting titanium and chromium in iron-rich plumes of a supernova remnant.

The neutrino-driven supernova model predicts that trapped neutrinos will generate plumes of high-entropy material, leading to bubbles in supernova remnants rich in metals such as titanium and chromium. That is exactly what Nagataki and his team saw in their spectral analysis based on observational data from the Chandra X-ray Observatory on Cassiopeia A (Fig. 1), a supernova remnant from about 350 years ago. This observation is thus strong confirmation that neutrinos play a role in driving supernova explosions.

“The chemical compositions we measured strongly suggest that these materials were driven by neutrino-driven winds from the surface of the neutron star,” says Nagataki. “Thus, the bubbles we found had been conveyed from the heart of the supernova to the outer rim of the supernova remnant.”

Nagataki’s team now intends to perform numerical simulations using supercomputers to model the process in more detail. “Our finding provides a strong impetus for revisiting the theory of supernova explosions,” Nagataki adds.

Related contents

• Radioactive elements in Cassiopeia A suggest a neutrino-driven explosion
• Rare-metal abundance points to a missing companion star for the supernova Cassiopeia A
• Clumpy structure in remnant probably formed in supernova explosion itself

Reference:

1.Sato, T., Maeda, K., Nagataki, S., Yoshida, T., Grefenstette, B., Williams, B. J., Umeda, H., Ono, M. & Hughes, J. P. High-entropy ejecta plumes in Cassiopeia A from neutrino-driven convection . Nature 592 537–540 (2021). doi: 10.1038/s41586-021-03391-9The webpage will open in a new tab.

Source: RIKEN/News

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The Clumpy and Lumpy Death of a Star

Tycho supernova remnant

Credit: X-ray: NASA/CXC/RIKEN & GSFC/T. Sato et al; Optical: DSS

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A Tour of Tycho's Supernova Remnant - More Animations

Astronomers now know that Tycho's new star was not new at all. Rather it signaled the death of a star in a supernova, an explosion so bright that it can outshine the light from an entire galaxy. This particular supernova was a Type Ia, which occurs when a white dwarf star pulls material from, or merges with, a nearby companion star until a violent explosion is triggered. The white dwarf star is obliterated, sending its debris hurtling into space.

As with many supernova remnants, the Tycho supernova remnant, as it's known today (or "Tycho," for short), glows brightly in X-ray light because shock waves — similar to sonic booms from supersonic aircraft — generated by the stellar explosion heat the stellar debris up to millions of degrees. In its two decades of operation, NASA's Chandra X-ray Observatory has captured unparalleled X-ray images of many supernova remnants. 

Chandra reveals an intriguing pattern of bright clumps and fainter areas in Tycho. What caused this thicket of knots in the aftermath of this explosion? Did the explosion itself cause this clumpiness, or was it something that happened afterward? 

This latest image of Tycho from Chandra is providing clues. To emphasize the clumps in the image and the three-dimensional nature of Tycho, scientists selected two narrow ranges of X-ray energies to isolate material (silicon, colored red) moving away from Earth, and moving towards us (also silicon, colored blue). The other colors in the image (yellow, green, blue-green, orange and purple) show a broad range of different energies and elements, and a mixture of directions of motion. In this new composite image, Chandra's X-ray data have been combined with an optical image of the stars in the same field of view from the Digitized Sky Survey.

By comparing the Chandra image of Tycho to two different computer simulations, researchers were able to test their ideas against actual data. One of the simulations began with clumpy debris from the explosion. The other started with smooth debris from the explosion and then the clumpiness appeared afterwards as the supernova remnant evolved and tiny irregularities were magnified.

A statistical analysis using a technique that is sensitive to the number and size of clumps and holes in images was then used. Comparing results for the Chandra and simulated images, scientists found that the Tycho supernova remnant strongly resembles a scenario in which the clumps came from the explosion itself. While scientists are not sure how, one possibility is that star's explosion had multiple ignition points, like dynamite sticks being set off simultaneously in different locations. 

Understanding the details of how these stars explode is important because it may improve the reliability of the use of Type Ia supernovas "standard candles" — that is, objects with known inherent brightness, which scientists can use to determine their distance. This is very important for studying the expansion of the universe. These supernovae also sprinkle elements such as iron and silicon, that are essential for life as we know it, into the next generation of stars and planets. 

A paper describing these results appeared in the July 10th, 2019 issue of The Astrophysical Journal and is available online. The authors are Toshiki Sato (RIKEN in Saitama, Japan, and NASA's Goddard Space Flight Center in Greenbelt, Maryland), John (Jack) Hughes (Rutgers University in Piscataway, New Jersey), Brian Williams, (NASA's Goddard Space Flight Center), and Mikio Morii (The Institute of Statistical Mathematics in Tokyo, Japan).

3D printed model of Tycho's Supernova Remnant

Credit: RIKEN/G. Ferrand, et al & NASA/CXC/SAO/A. Jubett, N. Wolk & K. Arcand

Another team of astronomers, led by Gilles Ferrand of RIKEN in Saitama, Japan, has constructed their own three-dimensional computer models of a Type Ia supernova remnant as it changes with time. Their work shows that initial asymmetries in the simulated supernova explosion are required so that the model of the ensuing supernova remnant closely resembles the Chandra image of Tycho, at a similar age. This conclusion is similar to that made by Sato and his team. 

A paper describing the results by Ferrand and co-authors appeared in the June 1st, 2019 issue of The Astrophysical Journal and is available online. 

NASA's Marshall Space Flight Center manages the  Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science and flight operations from Cambridge, Massachusetts.

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Fast Facts for Tycho's Supernova Remnant:

Scale: Image is about 12 arcmin (45 light years) across.
Category: Supernovas & Supernova Remnants
Coordinates (J2000):  RA 00h 25m 17s | Dec +64° 08' 37"
Constellation:  Cassiopeia
Observation Date: 14 pointings between Oct 1, 2001 & April 22, 2016
Observation Time: 336 hours 2 minutes (14 days 0 hours 2 minutes)
Obs. ID: 115, 3837, 7539, 8551, 10093-10097; 10902-10904; 10906, 15998
Instrument: ACIS
Also Known As:  G120.1+01.4, SN 1572
References: Sato, T. et al. 2019, ApJ, 879, 64; arXiv:1903.00764
Color Code: X-ray Broadband: Red: 0.3-1.2 keV, Yellow: 1.2-1.6 keV, Cyan: 1.6-2.26 keV, Navy: 2.2-4.1 keV, Purple: 4.4-6.1 keV; X-ray Motion Shift Orange: 1.7666-1.7812 keV, Blue: 1.9564-1.971 keV; Optical: Red, Blue
Distance Estimate:  About 13,000 light years

Source: NASA’s Chandra X-ray Observatory

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