A scientist discovers an ancient white dwarf star with enigmatic dust rings

February 19, 2019

Adam Schneider, astronomer of the USS, helps the research team to focus on a confusing astrophysical object

A volunteer working for the Backyard Worlds: Planet 9 project led by NASA discovered the oldest and coldest white dwarf known – an old vestige of the size of a solar star resembling the sun that is dead – surrounded dust and debris. Astronomers suspect that it would be the first known white dwarf with several rings of dust.

The star, LSPM J0207 + 3331 or J0207, is forcing researchers to reconsider models of planetary systems and could help us learn more about the distant future of our solar system.

Adam Schneider, a researcher at the School of Earth and Space Exploration at Arizona State University, was part of the team that unveiled the findings of the discovery to paint a picture of the surprising details of the white dwarf.

Worlds of the backyard: Planet 9 is a project led by Marc Kuchner, astrophysicist at NASA's Goddard Space Flight Center. Launched two years ago, it uses volunteers to sort infrared data for new discoveries with the help of an online interface and a search engine.

"This object was found by Melina Thevenot of Germany using the Backyard Worlds project," he said. "Initially, she thought that it could be a cold brown dwarf, which interests the project a lot and that he has been very successful at finding."

Brown dwarfs are low-temperature objects, too big to be planets but too small to be stars. They glow faintly at far infrared wavelengths and, because of their low light, are all relatively close to the sun.

"When Melina conducted further investigation, she discovered that even though the object had a significant infrared brightness, it was not a brown dwarf nearby," Schneider said. . Instead, it had to be something brighter and farther away, and the best candidate was a remnant of stellar evolution: a white dwarf star.

"The team looked at the situation together and we determined that it was probably a white dwarf with an excess of infrared," Schneider said.

Old star, hot rings

Excess was believed to radiate from a hot and dusty circumstellar disk. Such discs are thought to result from the continual fragmentation of small rocky planetesimals in orbit around the white dwarf. Yet, with an age of about 3 billion years, J0207 is colder and almost three times older than any other white dwarf known to house such a disc.

"However, we were experts in brown dwarfs and not experts in white dwarves, so we had to phone a friend and contact the white dwarf expert John Debes to ask him for help in interpreting this. that Melina had discovered, "said Schneider.

Debes is an astronomer at the Institute of Space Telescope Sciences in Baltimore.

Image above: Backyard Worlds: Planet 9 volunteers explore NASA's infrared images, looking for animated flashes to search for moving objects. Like other white dwarf stars, J0207 has a bluish hue in visible light (top), but also has an orange hue in the infrared (below), indicating the unexpected presence of circumstellar dust rings. Credit: Digitized Sky / WISE / NEOWISE Survey, Aaron Meisner (NOAO)

"This white dwarf is so old that whatever the process of feeding material to its rings, it has to run on time scales of a billion years," said Debes. "Most of the models that scientists have created to explain the rings around white dwarfs only work up to about 100 million years ago, so this star challenges our assumptions about how planetary systems evolve. "

By adding to the puzzle, the J0207 disc can be composed of more than one distinctive ring-shaped component, an arrangement never seen before in a circumstellar material surrounding a white dwarf.

To study the rings and their structure, Debes and Kuchner contacted collaborator Adam Burgasser of the University of California, San Diego to obtain follow-up observations with the Keck II telescope at the WM Observatory. Keck in Hawaii.

Keck's observations confirmed the recording properties of J0207. Now scientists are left puzzled as to how this fits into their models.

Debes compared the population of asteroid belt analogues in white dwarf systems to sand grains of an hourglass. Initially, there is a constant flow of material. The planets throw asteroids at the white dwarf to be torn apart, keeping a dusty disc. But over time, the asteroid belt is exhausted, just like grains of sand in the hourglass. Finally, all the contents of the disc fall on the surface of the white dwarf. Therefore, older white dwarfs like J0207 should be less likely to have discs or rings.

Monitoring future missions such as NASA's James Webb Space Telescope could help astronomers unravel the building blocks of the ring.

Backyard Worlds: Planet 9 bigger and better

The publication of the article in Astrophysical Journal Letters describing the star and the rings of the white dwarf coincides with a major upgrade of the original Backyard Worlds: Planet 9 project.

The database that volunteers are looking for comes from NASA's WISE satellite telescope. WISE, an acronym for Wide-field Infrared Survey Explorer, was launched in late 2009 and has mapped the entire sky many times over the last 10 years. WISE detects infrared light, the type of light emitted by objects at room temperature, such as planets, brown dwarfs and dusty rings around white dwarfs.

"We built Backyard Worlds: Planet 9 primarily to search for brown dwarfs and new planets in the solar system," said Kuchner. "But working with citizen scientists always gives rise to surprises – they are voracious – the project just celebrated its second birthday and has already discovered more than 1,000 likely brown dwarfs – now that we have restarted the website with twice as much from WISE data, we look forward to discovering even more exciting discoveries. "

For Schneider ASU, the more the better.

"My job is to examine the candidates found by the citizens, to prioritize them for follow-up and to organize the observations – it's like a place at the forefront for discoveries," he said.

Backyard Worlds: Planet 9 is a collaboration between NASA, the American Museum of Natural History in New York, Arizona State University, the National Observatory of Optical Astronomy, the Space Telescope Science Baltimore Institute, University of California at San Diego, Bucknell University, University of Oklahoma and Zooniverse, a collaboration of scientists, software developers and educators who develop and manage collectively citizen science projects on the Internet.

NASA's Jet Propulsion Laboratory in Pasadena, California, manages and operates WISE on behalf of NASA's Science Missions Directorate. The WISE mission was competitively selected as part of NASA's Explorers program, managed by the agency's Goddard Space Flight Center. The scientific instrument was built by the space dynamics laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colorado. Scientific operations and data processing take place at Caltech 's infrared processing and analysis center, which manages the JPL for NASA.

Top Photo: The star, designated LSPM J0207 + 3331, is the oldest and coolest white dwarf known to be surrounded by a dusty debris ring. This illustration describes the ring with two separate components, which scientists say best explains the infrared signal of the system, as well as an asteroid broken by the gravity of the white dwarf. Image: NASA Goddard Space Flight Center / Scott Wiessinger

Robert Burnham

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