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By NASA
Explore Hubble Science Hubble Space Telescope NASA’s Hubble Uncovers Rare… 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 Hubble’s Partners in Science Universe Uncovered AI and Hubble Science Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations 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 5 min read
NASA’s Hubble Uncovers Rare White Dwarf Merger Remnant
This is an illustration of a white dwarf star merging into a red giant star. A bow shock forms as the dwarf plunges through the star’s outer atmosphere. The passage strips down the white dwarf’s outer layers, exposing an interior carbon core. Artwork: NASA, ESA, STScI, Ralf Crawford (STScI) An international team of astronomers has discovered a cosmic rarity: an ultra-massive white dwarf star resulting from a white dwarf merging with another star, rather than through the evolution of a single star. This discovery, made by NASA’s Hubble Space Telescope’s sensitive ultraviolet observations, suggests these rare white dwarfs may be more common than previously suspected.
“It’s a discovery that underlines things may be different from what they appear to us at first glance,” said the principal investigator of the Hubble program, Boris Gaensicke, of the University of Warwick in the United Kingdom. “Until now, this appeared as a normal white dwarf, but Hubble’s ultraviolet vision revealed that it had a very different history from what we would have guessed.”
A white dwarf is a dense object with the same diameter as Earth, and represents the end state for stars that are not massive enough to explode as core-collapse supernovae. Our Sun will become a white dwarf in about 5 billion years.
In theory, a white dwarf can have a mass of up to 1.4 times that of the Sun, but white dwarfs heavier than the Sun are rare. These objects, which astronomers call ultra-massive white dwarfs, can form either through the evolution of a single massive star or through the merger of a white dwarf with another star, such as a binary companion.
This new discovery, published in the journal Nature Astronomy, marks the first time that a white dwarf born from colliding stars has been identified by its ultraviolet spectrum. Prior to this study, six white dwarf merger products were discovered via carbon lines in their visible-light spectra. All seven of these are part of a larger group that were found to be bluer than expected for their masses and ages from a study with ESA’s Gaia mission in 2019, with the evidence of mergers providing new insights into their formation history.
Astronomers used Hubble’s Cosmic Origins Spectrograph to investigate a white dwarf called WD 0525+526. Located 128 light-years away, it is 20% more massive than the Sun. In visible light, the spectrum of WD 0525+526’s atmosphere resembled that of a typical white dwarf. However, Hubble’s ultraviolet spectrum revealed something unusual: evidence of carbon in the white dwarf’s atmosphere.
White dwarfs that form through the evolution of a single star have atmospheres composed of hydrogen and helium. The core of the white dwarf is typically composed mostly of carbon and oxygen or oxygen and neon, but a thick atmosphere usually prevents these elements from appearing in the white dwarf’s spectrum.
When carbon appears in the spectrum of a white dwarf, it can signal a more violent origin than the typical single-star scenario: the collision of two white dwarfs, or of a white dwarf and a subgiant star. Such a collision can burn away the hydrogen and helium atmospheres of the colliding stars, leaving behind a scant layer of hydrogen and helium around the merger remnant that allows carbon from the white dwarf’s core to float upward, where it can be detected.
WD 0525+526 is remarkable even within the small group of white dwarfs known to be the product of merging stars. With a temperature of almost 21,000 kelvins (37,000 degrees Fahrenheit) and a mass of 1.2 solar masses, WD 0525+526 is hotter and more massive than the other white dwarfs in this group.
WD 0525+526’s extreme temperature posed something of a mystery for the team. For cooler white dwarfs, such as the six previously discovered merger products, a process called convection can mix carbon into the thin hydrogen-helium atmosphere. WD 0525+526 is too hot for convection to take place, however. Instead, the team determined a more subtle process called semi-convection brings a small amount of carbon up into WD 0525+526’s atmosphere. WD 0525+526 has the smallest amount of atmospheric carbon of any white dwarf known to result from a merger, about 100,000 times less than other merger remnants.
The high temperature and low carbon abundance mean that identifying this white dwarf as the product of a merger would have been impossible without Hubble’s sensitivity to ultraviolet light. Spectral lines from elements heavier than helium, like carbon, become fainter at visible wavelengths for hotter white dwarfs, but these spectral signals remain bright in the ultraviolet, where Hubble is uniquely positioned to spot them.
“Hubble’s Cosmic Origins Spectrograph is the only instrument that can obtain the superb quality ultraviolet spectroscopy that was required to detect the carbon in the atmosphere of this white dwarf,” said study lead Snehalata Sahu from the University of Warwick.
Because WD 0525+526’s origin was revealed only once astronomers glimpsed its ultraviolet spectrum, it’s likely that other seemingly “normal” white dwarfs are actually the result of cosmic collisions — a possibility the team is excited to explore in the future.
“We would like to extend our research on this topic by exploring how common carbon white dwarfs are among similar white dwarfs, and how many stellar mergers are hiding among the normal white dwarf family,” said study co-leader Antoine Bedrad from the University of Warwick. “That will be an important contribution to our understanding of white dwarf binaries, and the pathways to supernova explosions.”
The Hubble Space Telescope has been operating for more than three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
To learn more about Hubble, visit: https://science.nasa.gov/hubble
Facebook logo @NASAHubble @NASAHubble Instagram logo @NASAHubble Related Images & Videos
White Dwarf Merger Illustration
This is an illustration of a white dwarf star merging into a red giant star. A bow shock forms as the dwarf plunges through the star’s outer atmosphere. The passage strips down the white dwarf’s outer layers, exposing an interior carbon core.
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Last Updated Aug 13, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Contact Media Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov
Ray Villard
Space Telescope Science Institute
Baltimore, Maryland
Bethany Downer
ESA/Hubble
Garching, Germany
Related Terms
Hubble Space Telescope Astrophysics Astrophysics Division Goddard Space Flight Center Stars The Universe White Dwarfs
Related Links and Documents
Science Paper: A hot white dwarf merger remnant revealed by an ultraviolet detection of carbon, PDF (23.45 MB)
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Hubble Space Telescope
Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
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By NASA
Astronaut Victor Glover interacts with an Orion spacecraft simulator during NASA’s “All-Star Shoot for the Stars” event at The Children’s Museum of Indianapolis on Saturday, July 18, 2025. Credit: NASA/Zach Lucas From astronauts to athletes, researchers to referees, and communicators to coaches, NASA is much like basketball – we all train to reach the top of our game. Staff from NASA’s Glenn Research Center in Cleveland drove home this point during the “All-Star Shoot for the Stars” event at The Children’s Museum of Indianapolis, July 17-19. As part of WNBA All-Star Game activities, this event highlighted NASA technology while illuminating the intersection of sports and STEM.
The event offered a captivating look into space exploration, thanks to the combined efforts of NASA and museum staff. Highlights included a detailed Orion exhibit, a new spacesuit display featuring five full-scale spacesuits, and virtual reality demonstrations. Visitors also had the chance to enjoy an interactive spacesuit app and a unique cosmic selfie station.
On Friday, July 18, 2025, visitors at NASA’s “All-Star Shoot for the Stars” event at The Children’s Museum of Indianapolis look at a new spacesuit display featuring five full-scale spacesuits. Credit: NASA/Christopher Richards The event was made even more memorable by Artemis II astronaut Victor Glover, who connected with visitors and posed for photos. WNBA legend Tamika Catchings also made a special appearance, inspiring attendees with a message to “aim high!”
“All Star Weekend presented an excellent opportunity to share NASA’s mission with the Indianapolis community and people across the Midwest who were in town for the game,” said Jan Wittry, Glenn’s news chief. “I saw children’s faces light up as they interacted with the exhibits and talked to NASA experts, sparking a curiosity among our potential future STEM workforce.”
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By NASA
For Melissa John, protecting the environment is her way of contributing to space exploration while preserving the Earth we call home.
As the sustainability program lead at NASA’s White Sands Test Facility in Las Cruces, New Mexico, John manages efforts to reduce waste, prevent pollution, and promote eco-conscious practices. Over the past 13 years, she has helped shape a workplace culture that values innovation and environmental responsibility.
Official portrait of Melissa John. NASA/Brandon Teeples This is how I make a difference — by protecting the land, the community, and hopefully inspiring others to do the same.
Melissa John
Sustainability Program Lead
Through awareness campaigns and outreach events, John empowers employees to be mindful of their environmental impact. Whether she is fostering grassroots connections, leading hands-on events, or recognizing colleagues who prioritize climate-aware actions, John remains dedicated to making a lasting, positive impact on the planet.
John credits her Diné heritage and cultural values for fueling her passion to protect and preserve Earth for future generations.
John began her NASA career at White Sands as a document specialist, reviewing schedules and environmental reports. She later transitioned into technical editing and gradually got involved in green initiatives, volunteering her time before eventually stepping into her current leadership role.
Now, she coordinates a sitewide working group dedicated to reducing the facility’s environmental impact and inspires others to think critically about everyday actions and their ripple effects.
Melissa John in the propulsion test area near the main water tank at NASA’s White Sands Test Facility in Las Cruces, New Mexico.NASA/Brandon Teeples John did not always know how she would make her mark.
“Growing up, I remember a teacher asking how we could make a difference in the world,” she said. “I never forgot that question.”
During the years she spent working in accounting and in the mining industry, she kept returning to that question. It was not until she joined NASA that she found her answer:
“This — this is how I make my difference in the world.”
The work also helped John grow in ways she did not expect.
“I was painfully shy as a kid and terrified of speaking in front of a crowd,” she said. “But when I took on this role, I knew I had to find my voice. I still have timid moments, but the pride I feel in this work helps me push through. I’ve been through a lot, but I’m still here learning, growing, and showing up for the team I now call family.”
John credits her strong support system for that transformation. “I am in awe of the women I’ve worked with,” she said. “I hope I can inspire others as they have inspired me.”
From left to right: Mary Canavan, Melissa John, Amanda Skarsgard, and Pam Egan at the annual Plant Fair Share at White Sands Test Facility. Whether on Earth or beyond it, John believes that thoughtful action today leads to a brighter tomorrow. She is committed to leaving the world a better place for the next generation. Her legacy is simple: “Clean air, clean water, and clean land — that’s what I want to pass on.”
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By Space Force
Space Systems Command has activated two new System Deltas within the mission area of the Space Force Program Executive Officer for Space Sensing.
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By NASA
The NASA Ames Science Directorate recognizes the outstanding contributions of (pictured left to right) Sigrid Reinsch, Lori Munar, Kevin Sims, and Matthew Fladeland. Their commitment to the NASA mission represents the entrepreneurial spirit, technical expertise, and collaborative disposition needed to explore this world and beyond.
Space Biosciences Star: Sigrid Reinsch
As Director of the SHINE (Space Health Impacts for the NASA Experience) program and Project Scientist for NBISC (NASA Biological Institutional Scientific Collection), Sigrid Reinsch is a high-performing scientist and outstanding mentor in the Space Biosciences Research Branch. Her dedication to student training and her efforts to streamline processes have significantly improved the experience of welcoming summer interns at NASA Ames.
Space Science and Astrobiology Star: Lori Munar
Lori Munar serves as the assistant Branch Chief of the Exobiology Branch. In the past few months, she has gone above and beyond to organize a facility and laboratory surplus event that involved multiple divisions over multiple days. The event resulted in considerable savings across the groups involved and improved the safety of N239 staff and the appearance of offices and labs.
Space Science and Astrobiology Star: Kevin Sims
Kevin Sims is a NASA Technical Project Manager serving the Astrophysics Branch as a member of the Flight Systems Implementation Branch in the Space Biosciences Division. Kevin is recognized for outstanding project management for exoplanet imaging instrumentation development in support of the Habitable Worlds Observatory. Kevin has streamlined, organized, and improved the efficiency of the Ames Photonics Testbed being developed as part the AstroPIC Early Career Initiative project.
Earth Science Star: Matthew Fladeland
Matthew Fladeland is a research scientist in the Earth Science Division managing NASA SMD’s Program Office for the Airborne Science Program, located at Ames. He is recognized for exemplary leadership and teamwork leading to new reimbursable agreements with the Department of Defense, for accelerating science technology solutions through the SBIR program, and for advancing partnerships with the US Forest Service on wildland ecology and fire science.
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