The oldest, coldest white dwarf known to be surrounded by a ring of dusty debris.

A citizen scientist working for NASA has found the oldest and coldest known white dwarf - an 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, is forcing researchers to reconsider models of planetary systems and could help us learn about the distant future of our solar system.

"This white dwarf is so old that whatever process is feeding material into its rings must operate on billion-year timescales," said John Debes, an astronomer at the Space Telescope Science Institute in Baltimore, working with the NASA-led Backyard Worlds: Planet 9 project.

"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," Debes added.

The findings were published in The Astrophysical Journal Letters.

J0207 is located around 145 light years away in the constellation Capricornus. White dwarfs slowly cool as they age, and Debes's team calculated J0207 is about three billion years old, based on a temperature just over 5,800 degrees Celsius.

Previously, dust disks and rings had only been observed surrounding white dwarfs about one-third J0207's age.

J0207's ring may even be multiple rings. Debes and his colleagues suggest there could be two distinct components - one thin ring just at the point where the star's tides break up the asteroids and a wider ring closer to the white dwarf.

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