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Astronomie - Citizen scientist finds ancient white dwarf star with enigmatic dust rings

21.02.2019

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A volunteer working with the NASA-led Backyard Worlds: Planet 9 project has found the oldest and coldest known white dwarf — an old Earth-sized remnant of a sun-like star that has died — ringed by dust and debris. Astronomers suspect this could be the first known white dwarf with multiple dust rings.

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

Adam Schneider, a research scientist at Arizona State University's School of Earth and Space Exploration, was part of the team that unwrapped the discovery data to draw a picture of the white dwarf's surprising details.

Backyard Worlds: Planet 9 is a project led by Marc Kuchner, an astrophysicist at NASA’s Goddard Space Flight Center. Launched two years ago, it enlists volunteers to sort through infrared data for new discoveries using an online interface and search engine.

"This object was found by Melina Thévenot of Germany using the Backyard Worlds project," he said. "She originally thought it might be a cold brown dwarf, something the project is very interested in and has had a lot of success finding."

Brown dwarfs are low-temperature objects too big to be planets yet too small to be stars. They shine dimly at far infrared wavelengths and because of their low luminosity, all those known lie relatively close to the sun.

"When Melina investigated further, she found that although the object had significant infrared brightness; it was not a nearby brown dwarf," Schneider said. Instead it had to be something brighter and farther away, and the best candidate was a stellar evolution remnant: a white dwarf star. 

"The team looked at it together, and we determined it was likely a white dwarf with infrared excess," said Schneider.

Old star, warm rings 

The excess was believed to be radiating from a warm, dusty circumstellar disk. Such disks are thought to result from the continual breakup of small rocky planetesimals orbiting the white dwarf. Yet with an age of roughly 3 billion years, J0207 is colder and nearly three times older than any other white dwarf known to harbor such a disk.

"However, we were brown dwarf experts and not white dwarf experts, so we needed to 'phone-a-friend' and contacted white dwarf expert John Debes for help interpreting what Melina had found," said Schneider.

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

Above image: Backyard Worlds: Planet 9 volunteers scour infrared images from NASA, searching animated blinks for moving objects. Like other white dwarf stars, J0207 shows a bluish tinge in visible light (top), but also sports an orange hue in the infrared (bottom), indicating the unexpected presence of circumstellar dust rings. Credit: Digitized Sky Survey/WISE/NEOWISE, Aaron Meisner (NOAO)

"This white dwarf is so old that whatever process is feeding material into its rings must operate on billion-year timescales," Debes said. "Most of the models scientists have created to explain rings around white dwarfs only work well up to around 100 million years, so this star is really challenging our assumptions of how planetary systems evolve."

Adding to the puzzle, the J0207 disk may be composed of more than one distinct ring-like component, an arrangement never before seen in circumstellar material surrounding a white dwarf.

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

The Keck observations helped confirm J0207’s record-setting properties. Now scientists are left to puzzle how it fits into their models.

Debes compared the population of asteroid belt analogs in white dwarf systems to the grains of sand in an hourglass. Initially, there’s a steady stream of material. The planets fling asteroids inward towards the white dwarf to be torn apart, maintaining a dusty disk. But over time, the asteroid belts become depleted, just like grains of sand in the hourglass. Eventually, all the material in the disk falls down onto the surface of the white dwarf, so older white dwarfs like J0207 should be less likely to have disks or rings.

Follow-up with future missions like NASA's James Webb Space Telescope may help astronomers tease apart the ring’s constituent parts.

Backyard Worlds: Planet 9 bigger and better

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

The database that volunteers search comes from NASA's WISE satellite telescope. WISE, which stands for Wide-field Infrared Survey Explorer, was launched in late 2009 and has mapped the entire sky numerous times over the past 10 years. WISE detects infrared light, the kind of light emitted by objects at room temperature, like planets, brown dwarfs — and dusty rings around white dwarfs. 

"We built Backyard Worlds: Planet 9 mostly to search for brown dwarfs and new planets in the solar system," Kuchner said. "But working with citizen scientists always leads to surprises. They are voracious — the project just celebrated its second birthday, and they’ve already discovered more than 1,000 likely brown dwarfs. Now that we’ve rebooted the website with double the amount of WISE data, we’re looking forward to even more exciting discoveries."

For ASU's Schneider, the more the better.

"My job is to weed through the candidates found by the citizens, prioritize them for follow-up, and help organize the observations. It's like a front-row seat 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, National Optical Astronomy Observatory, the Space Telescope Science Institute in Baltimore, the University of California San Diego, Bucknell University, the University of Oklahoma, and Zooniverse, a collaboration of scientists, software developers and educators who collectively develop and manage citizen science projects on the internet.

NASA's Jet Propulsion Laboratory in Pasadena, California, manages and operates WISE for NASA's Science Mission Directorate. The WISE mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colorado. Science operations and data processing take place at the Infrared Processing and Analysis Center at Caltech, which manages JPL for NASA.

Quelle: ASU New American University

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German NASA volunteer finds oldest white dwarf star

A German volunteer scientist working with a NASA-led project has stumbled upon a white dwarf star 145 light years away. NASA believes the discovery could "help us learn about the distant future of our solar system."

Melina Thevenot, a volunteer scientist working with NASA's Backyard Worlds: Planet 9 project, has found the oldest and coldest known white dwarf star, the US space administration has announced.

The star, named J0207, is an Earth-sized remnant of a sun-like star located 145 light years away in the Capricornus constellation. Due to its temperature of 5,800 degrees Celsius (10,500 Fahrenheit), NASA believes the star is about 3 billion years old.

Read more: What you can see in space in 2019

NASA said in a statement on Tuesday that Thevenot's discovery "is forcing researchers to reconsider models of planetary systems and could help us learn about the distant future of our solar system."

Thevenot, a citizen scientist from Germany, had been searching for brown dwarfs, which are larger than planets but smaller than stars, while working in the European Space Agency's archives when she found something much brighter and much further away.

She initially thought it was bad data, according to NASA, but passed her findings to astronomer John Debes and astrophysicist Marc Kuchner, both of whom are based in Maryland. They then contacted Adam Burgasser, a collaborator with the University of California, San Diego, to use the Keck II telescope in Hawaii to study the white dwarf.

"That is a really motivating aspect of the search," said Thevenot as part of NASA's statement. "The researchers will move their telescopes to look at worlds you have discovered. What I especially enjoy, though, is the interaction with the awesome research team. Everyone is very kind, and they are always trying to make the best out of our discoveries."

Kuchner, the leader of the Backyard Worlds project, said working with citizen scientists "always leads to surprises."

Quelle: DW

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