Professional astronomers and volunteers working with the Backyard Worlds: Planet 9 Citizen Science Project have identified the oldest and coldest white dwarf known, surrounded by dust and debris. The discovery is described in an article from Letters from the Astrophysical Journal.
The newly discovered white dwarf, named LSPM J0207 + 3331, is located about 145 light-years from the constellation Capricorn.
White dwarfs cool slowly as they get older, and astronomers calculated that the object was about 3 billion years old, based on a temperature of just over 10,500 degrees Fahrenheit (5,800 degrees Celsius).
A strong infrared signal picked up by NASA's Wide-field Infrared Survey Explorer (WISE) suggested the presence of dust, making the LSPM J0207 + 3331 the white dwarf with the oldest and coldest dust ever known.
Previously, dust disks and rings had been observed around white dwarves only about a third of the age of LPSM J0207 + 3331.
"This white dwarf is so old that any process that feeds its rings into materials must operate on time scales of billions of years," said Dr. John Debes, astronomer at the Space Telescope Science Institute.
"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. "
When a Sun-like star runs out of fuel, it swells into a red giant, ejects at least half of its mass, and leaves behind a very hot white dwarf. During the giant phase of the star, planets and asteroids close to the star are engulfed and incinerated.
The more distant planets and asteroids survive, but move outward as their orbits grow. This is because when the star loses mass, its gravitational influence on surrounding objects is greatly reduced.
Some white dwarfs – between 1 and 4% – show an infrared emission indicating that they are surrounded by dusty discs or rings. Astronomers believe that dust can come from distant asteroids and comets close to the star by gravitational interactions with displaced planets.
As these small bodies approach the white dwarf, the star's high severity tears them into a process called low tide. Debris forms a ring of dust that will slowly wrap on the surface of the star.
LSPM J0207 + 3331 was first noticed by Melina Thévenot, a citizen scientist working for the Backyard Worlds: Planet 9 project.
"It's a very motivating aspect of the research," said Thevenot.
"The researchers will move their telescopes to look at the worlds you have discovered. What I particularly like is the interaction with the great research team. Everyone is very nice and always tries to make the most of our discoveries. "
According to astronomers, the LPSM ring J0207 + 3331 could even be composed of several rings.
They suggest that there could be two separate components, a ring ending at the point where the star tides break asteroids and a wider ring closer to the white dwarf.
Monitoring future missions such as NASA's James Webb Space Telescope could help them unravel the building blocks of the ring.
John H. Debes et al. 2019. A 3 Gyr white dwarf with hot dust discovered as part of the Back 9 World: Planet 9 Citizen Science project. ApJL 872, L25; doi: 10.3847 / 2041-8213 / ab0426