A volunteer of the Citizen Science project Backyard Worlds: Planet 9 has discovered the oldest and coldest known white dwarf surrounded by dust. The dust is organized in a ring, possibly even multiple ones, that have lasted for what seems to be billions of years. And that doesn’t fit with our models.
The white dwarf, known as LSPM J0207+3331 or J0207 for short, is located 145 light-years away in the constellation Capricornus. White dwarfs are stellar remnants, the final stage of evolution for many small stars. They are dense stellar cores, made of degenerate matter, and not much bigger than Earth. The objects slowly radiate energy away and get colder as they age. J0207 is estimated to be 3 billion years old and 5,800°C (10,500°F). As reported in The Astrophysical Journal Letters, the team now needs to reconsider models of planetary evolution around white dwarfs.
“This white dwarf is so old that whatever process is feeding material into its rings must operate on billion-year timescales,” lead author John Debes, an astronomer at the Space Telescope Science Institute, said in a statement. “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.”
When stars like the Sun run out of fuel in their core, they swell up into large red giants. Some planets are incinerated by this, while others survive. The big stars lose mass quite quickly, with their gravitational influence on the planet becoming weaker, leading to planets migrating to wider orbits. This could lead to asteroids and comets shifting into closer orbits. So far, these dusty disks are only seen in a few percent of white dwarfs observed.
The discovery is part of the Backyard World: Planet 9 project, which is being used to look for the hypothetical ninth planet of the Solar System. The project has also been used to discover many brown dwarfs in our corner of the galaxy. Melina Thévenot, the citizen scientist that discovered J0207, realized that this object was no brown dwarf and passed on her findings to the science team, who followed up with the Keck telescope.
“That is a really motivating aspect of the search,” said Thévenot, one of more than 150,000 citizen scientists on the Backyard Worlds project. “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.”
The project has been going on for over two years, with more than 1,000 likely brown dwarfs discovered.