ASU astronomer Adam Schneider and citizen scientist volunteers at a NASA run project Panet 9has found the oldest and coldest known white dwarf. 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.
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.
"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.
Link to abstract; https://iopscience.iop.org/article/10.3847/2041-8213/ab0426
Article sourced from; asunow.asu.edu