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Hubble Probes the Complex History of a Dying Star
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By NASA
NASA/Nichole Ayers On July 26, 2025, NASA astronaut Nichole Ayers took this long-exposure photograph – taken over 31 minutes from a window inside the International Space Station’s Kibo laboratory module – capturing the circular arcs of star trails.
In its third decade of continuous human presence, the space station has a far-reaching impact as a microgravity lab hosting technology, demonstrations, and scientific investigations from a range of fields. The research done on the orbiting laboratory will inform long-duration missions like Artemis and future human expeditions to Mars.
Image credit: NASA/Nichole Ayers
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By NASA
Explore Hubble Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Universe Uncovered Hubble’s Partners in Science AI and Hubble Science Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Astronaut Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts Multimedia Images Videos Sonifications Podcasts e-Books Online Activities 3D Hubble Models Lithographs Fact Sheets Posters Hubble on the NASA App Glossary News Hubble News Social Media Media Resources More 35th Anniversary Online Activities 2 min read
Hubble Homes in on Galaxy’s Star Formation
This NASA/ESA Hubble Space Telescope image features the asymmetric spiral galaxy Messier 96. ESA/Hubble & NASA, F. Belfiore, D. Calzetti This NASA/ESA Hubble Space Telescope image features a galaxy whose asymmetric appearance may be the result of a galactic tug of war. Located 35 million light-years away in the constellation Leo, the spiral galaxy Messier 96 is the brightest of the galaxies in its group. The gravitational pull of its galactic neighbors may be responsible for Messier 96’s uneven distribution of gas and dust, asymmetric spiral arms, and off-center galactic core.
This asymmetric appearance is on full display in the new Hubble image that incorporates data from observations made in ultraviolet, near infrared, and visible/optical light. Earlier Hubble images of Messier 96 were released in 2015 and 2018. Each successive image added new data, building up a beautiful and scientifically valuable view of the galaxy.
The 2015 image combined two wavelengths of optical light with one near infrared wavelength. The optical light revealed the galaxy’s uneven form of dust and gas spread asymmetrically throughout its weak spiral arms and its off-center core, while the infrared light revealed the heat of stars forming in clouds shaded pink in the image.
The 2018 image added two more optical wavelengths of light along with one wavelength of ultraviolet light that pinpointed areas where high-energy, young stars are forming.
This latest version offers us a new perspective on Messier 96’s star formation. It includes the addition of light that reveals regions of ionized hydrogen (H-alpha) and nitrogen (NII). This data helps astronomers determine the environment within the galaxy and the conditions in which stars are forming. The ionized hydrogen traces ongoing star formation, revealing regions where hot, young stars are ionizing the gas. The ionized nitrogen helps astronomers determine the rate of star formation and the properties of gas between stars, while the combination of the two ionized gasses helps researchers determine if the galaxy is a starburst galaxy or one with an active galactic nucleus.
The bubbles of pink gas in this image surround hot, young, massive stars, illuminating a ring of star formation in the galaxy’s outskirts. These young stars are still embedded within the clouds of gas from which they were born. Astronomers will use the new data in this image to study how stars are form within giant dusty gas clouds, how dust filters starlight, and how stars affect their environments.
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Claire Andreoli (claire.andreoli@nasa.gov)
NASA’s Goddard Space Flight Center, Greenbelt, MD
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Last Updated Aug 29, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
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Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
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By NASA
This graphic features data from NASA’s Chandra X-ray Observatory of the Cassiopeia A (Cas A) supernova remnant that reveals that the star’s interior violently rearranged itself mere hours before it exploded. The main panel of this graphic is Chandra data that shows the location of different elements in the remains of the explosion: silicon (represented in red), sulfur (yellow), calcium (green) and iron (purple). The blue color reveals the highest-energy X-ray emission detected by Chandra in Cas A and an expanding blast wave. The inset reveals regions with wide ranges of relative abundances of silicon and neon. This data, plus computer modeling, reveal new insight into how massive stars like Cas A end their lives.X-ray: NASA/CXC/Meiji Univ./T. Sato et al.; Image Processing: NASA/CXC/SAO/N. Wolk The inside of a star turned on itself before it spectacularly exploded, according to a new study from NASA’s Chandra X-ray Observatory. Today, this shattered star, known as the Cassiopeia A supernova remnant, is one of the best-known, well-studied objects in the sky.
Over three hundred years ago, however, it was a giant star on the brink of self-destruction. The new Chandra study reveals that just hours before it exploded, the star’s interior violently rearranged itself. This last-minute shuffling of its stellar belly has profound implications for understanding how massive stars explode and how their remains behave afterwards.
Cassiopeia A (Cas A for short) was one of the first objects the telescope looked at after its launch in 1999, and astronomers have repeatedly returned to observe it.
“It seems like each time we closely look at Chandra data of Cas A, we learn something new and exciting,” said Toshiki Sato of Meiji University in Japan who led the study. “Now we’ve taken that invaluable X-ray data, combined it with powerful computer models, and found something extraordinary.”
As massive stars age, increasingly heavy elements form in their interiors by nuclear reactions, creating onion-like layers of different elements. Their outer layer is mostly made of hydrogen, followed by layers of helium, carbon and progressively heavier elements – extending all the way down to the center of the star.
Once iron starts forming in the core of the star, the game changes. As soon as the iron core grows beyond a certain mass (about 1.4 times the mass of the Sun), it can no longer support its own weight and collapses. The outer part of the star falls onto the collapsing core, and rebounds as a core-collapse supernova.
The new research with Chandra data reveals a change that happened deep within the star at the very last moments of its life. After more than a million years, Cas A underwent major changes in its final hours before exploding.
“Our research shows that just before the star in Cas A collapsed, part of an inner layer with large amounts of silicon traveled outwards and broke into a neighboring layer with lots of neon,” said co-author Kai Matsunaga of Kyoto University in Japan. “This is a violent event where the barrier between these two layers disappears.”
This upheaval not only caused material rich in silicon to travel outwards; it also forced material rich in neon to travel inwards. The team found clear traces of these outward silicon flows and inward neon flows in the remains of Cas A’s supernova remnant. Small regions rich in silicon but poor in neon are located near regions rich in neon and poor in silicon.
The survival of these regions not only provides critical evidence for the star’s upheaval, but also shows that complete mixing of the silicon and neon with other elements did not occur immediately before or after the explosion. This lack of mixing is predicted by detailed computer models of massive stars near the ends of their lives.
There are several significant implications for this inner turmoil inside of the doomed star. First, it may directly explain the lopsided rather than symmetrical shape of the Cas A remnant in three dimensions. Second, a lopsided explosion and debris field may have given a powerful kick to the remaining core of the star, now a neutron star, explaining the high observed speed of this object.
Finally, the strong turbulent flows created by the star’s internal changes may have promoted the development of the supernova blast wave, facilitating the star’s explosion.
“Perhaps the most important effect of this change in the star’s structure is that it may have helped trigger the explosion itself,” said co-author Hiroyuki Uchida, also of Kyoto University. “Such final internal activity of a star may change its fate—whether it will shine as a supernova or not.”
These results have been published in the latest issue of The Astrophysical Journal and are available online.
To learn more about Chandra, visit:
https://science.nasa.gov/chandra
Read more from NASA’s Chandra X-ray Observatory Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
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.
News Media Contact
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
Corinne Beckinger
Marshall Space Flight Center, Huntsville, Alabama
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corinne.m.beckinger@nasa.gov
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Last Updated Aug 28, 2025 EditorLee MohonContactCorinne M. Beckingercorinne.m.beckinger@nasa.govLocationMarshall Space Flight Center Related Terms
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By European Space Agency
The NASA/ESA/CSA James Webb Space Telescope has revealed new details in the core of the Butterfly Nebula, NGC 6302. From the dense, dusty torus that surrounds the star hidden at the centre of the nebula to its outflowing jets, the Webb observations reveal many new discoveries that paint a never-before-seen portrait of a dynamic and structured planetary nebula.
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By NASA
A scanning electron microscope image of a micrometeorite impact crater in a particle of asteroid Bennu material. Credits: NASA/Zia Rahman 5 min read
NASA’s Bennu Samples Reveal Complex Origins, Dramatic Transformation
Asteroid Bennu, sampled by NASA’s OSIRIS-REx mission in 2023, is a mixture of dust that formed in our solar system, organic matter from interstellar space, and pre-solar system stardust. Its unique and varied contents were dramatically transformed over time by interactions with water and exposure to the harsh space environment.
These insights come from a trio of newly published papers based on the analysis of Bennu samples by scientists at NASA and other institutions.
Bennu is made of fragments from a larger parent asteroid destroyed by a collision in the asteroid belt, between the orbits of Mars and Jupiter. One of the papers, co-led by Jessica Barnes at the University of Arizona, Tucson, and Ann Nguyen of NASA’s Johnson Space Center in Houston and published in the journal Nature Astronomy, suggests that Bennu’s ancestor was made up of material that had diverse origins—near the Sun, far from the Sun, and even beyond our solar system.
The analyses show that some of the materials in the parent asteroid, despite very low odds, escaped various chemical processes driven by heat and water and even survived the extremely energetic collision that broke it apart and formed Bennu.
“We traced the origins of these initial materials accumulated by Bennu’s ancestor,” said Nguyen. “We found stardust grains with compositions that predate the solar system, organic matter that likely formed in interstellar space, and high temperature minerals that formed closer to the Sun. All of these constituents were transported great distances to the region that Bennu’s parent asteroid formed.”
The chemical and atomic similarities of samples from Bennu, the asteroid Ryugu (sampled by JAXA’s (the Japan Aerospace Exploration Agency) Hayabusa2 mission) and the most chemically primitive meteorites collected on Earth suggest their parent asteroids may have formed in a similar, distant region of the early solar system. Yet the differences from Ryugu and meteorites that were seen in the Bennu samples may indicate that this region changed over time or did not mix as well as some scientists have thought.
We found stardust grains with compositions that predate the solar system, organic matter that likely formed in interstellar space, and high temperature minerals that formed closer to the Sun.
Ann Nguyen
Planetary Scientist
Though some original constituents survived, most of Bennu’s materials were transformed by reactions with water, as reported in the paper co-led by Tom Zega of the University of Arizona and Tim McCoy of the Smithsonian’s National Museum of Natural History in Washington and published in Nature Geoscience. In fact, minerals in the parent asteroid likely formed, dissolved, and reformed over time.
“Bennu’s parent asteroid accumulated ice and dust. Eventually that ice melted, and the resulting liquid reacted with the dust to form what we see today, a sample that is 80% minerals that contain water,” said Zega. “We think the parent asteroid accumulated a lot of icy material from the outer solar system, and then all it needed was a little bit of heat to melt the ice and cause liquids to react with solids.”
Bennu’s transformation did not end there. The third paper, co-led by Lindsay Keller at NASA Johnson and Michelle Thompson of Purdue University, also published in Nature Geoscience, found microscopic craters and tiny splashes of once-molten rock – known as impact melts – on the sample surfaces, signs that the asteroid was bombarded by micrometeorites. These impacts, together with the effects of solar wind, are known as space weathering and occurred because Bennu has no atmosphere to protect it.
“The surface weathering at Bennu is happening a lot faster than conventional wisdom would have it, and the impact melt mechanism appears to dominate, contrary to what we originally thought,” said Keller. “Space weathering is an important process that affects all asteroids, and with returned samples, we can tease out the properties controlling it and use that data and extrapolate it to explain the surface and evolution of asteroid bodies that we haven’t visited.”
Ann Nguyen, co-lead author of a new paper that gives insights into the diverse origin of asteroid Bennu’s “parent” asteroid works alongside the NanoSIMS 50L (nanoscale secondary ion mass spectrometry) ion microprobe in the Astromaterials Research and Exploration Science Division at NASA’s Johnson Space Center in Houston. Credit: NASA/James Blair As the leftover materials from planetary formation 4.5 billion years ago, asteroids provide a record of the solar system’s history. But as Zega noted, we’re seeing that some of these remnants differ from what has been found in meteorites on Earth, because certain types of asteroids burn up in the atmosphere and never make it to the ground. That, the researchers point out, is why collecting actual samples is so important.
“The samples are really crucial for this work,” Barnes said. “We could only get the answers we got because of the samples. It’s super exciting that we’re finally able to see these things about an asteroid that we’ve been dreaming of going to for so long.”
The next samples NASA expects to help unravel our solar system’s story will be Moon rocks returned by the Artemis III astronauts.
NASA’s Goddard Space Flight Center provided overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator. The university leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Littleton, Colorado, built the spacecraft and provided flight operations. Goddard and KinetX Aerospace were responsible for navigating the OSIRIS-REx spacecraft. Curation for OSIRIS-REx takes place at NASA’s Johnson Space Center in Houston. International partnerships on this mission include the OSIRIS-REx Laser Altimeter instrument from the Canadian Space Agency and asteroid sample science collaboration with JAXA’s Hayabusa2 mission. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.
Melissa Gaskill
Johnson Space Center
For more information on NASA’s OSIRIS-REx mission, visit:
https://science.nasa.gov/mission/osiris-rex/
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Victoria Segovia
Johnson Space Center
(281) 483-5111
victoria.segovia@nasa.gov
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