Scientists Found an Ancient White Dwarf, J0207, with Multiple Dust Rings

The Backyard Worlds: Planet 9 project observed rings of debris and dust around an Earth-sized white dwarf star, called J0207.

LSPM J0207+3331, which is usually known as the J0207, is the oldest and coldest white dwarf star known to humanity. Recently, research led by NASA showed multiple rings of dust around this white dwarf and the findings were published in the journal ‘The Astrophysical Journal Letters’. John Debes, an Astronomer at the Space Telescope Science Institute who led the research, mentioned that it is the first incident that such an old star with rings is located and its discovery has forced the scientists to reconsider the models of planetary systems. He referred to that thought in the following words:

“This white dwarf is so old that whatever process is feeding material into its rings must operate on billion-year timescales. 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.”

Location of J0207

J0207 is located in the constellation Capricornus at a distance of about 145 light-years. According to the calculations of the researching team, it is around 3 billion years old. The age of white dwarfs is calculated by referring to their temperatures because they slowly cool as they age. It was found that it was nearly at 5,800^o C at the time of its discovery. The Wide-field Infrared Survey Explorer (WISE) of NASA detected a strong infrared signal to determine the presence of dust rings around J0207. Prior to this discovery, dust rings and disks had only been observed surrounding white dwarfs about one-third the age of J0207.

Formation of White Dwarfs

A white dwarf is usually born when a Sun-like star runs out of fuel. The star initially turns into a massive red giant before ejecting half of its mass to leave behind an incredibly hot white dwarf star. The asteroids and planets that are in the vicinity of this star are engulfed over time while the ones that are far away from it move outwards as the gravitational influence of the white dwarf is significantly less than the original star. That’s the reason why scientists believe that our Sun will swallow Mercury, Venus, and eventually Earth in the next 5 billion years.

Despite all that, some of the white dwarfs (like J0207) seems to have dusty rings around them. A popular theory suggests that this dust comes from distant asteroids and comets. The gravitational attraction of the star pulls these bodies towards the white dwarf. Once these objects come too close to the star, the strength of the gravitational force tears them apart (Tidal Disruption). The debris produced forms a ring of dust, which ultimately lands onto the surface of the white dwarf.

Infrared Signal of J0207

Melina Thévenot, a Citizen Scientist in Germany who is also a Co-author of the paper, initially considered the infrared signal of J0207 a bad data. She found the signal in the archives of the Gaia Satellite while she was searching for brown dwarfs. Upon examining the source of J0207, she found that it was too bright and too far away to be a brown dwarf. Consequently, she passed the data to the team of Backyard Worlds: Planet 9. She explained her experience by saying,

“That is a really motivating aspect of the search. The researchers will move their telescopes to look at the 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 senior member of the researching team, including Debes, obtained follow-up observations from the Keck II Telescope at the W.M Keck Observatory to confirm the special characteristics of J0207. Once it was confirmed that J0207 is a white dwarf with dust rings around it, the next challenge researchers faced was to fit the discovery into their existing models.

J0207 and Existing Models

In order to do that, Debes compared the asteroid belt analogs in white dwarf systems to the grains of sand in an hourglass. He deduced that eventually, all the material in the disk will fall onto the surface of the white dwarf which means that older stars should be less likely to host these dust rings. He proposed that there are two rings. One of them is closer to the star and is much wider than its companion. On the other hand, the outer ring is thin and is situated at the point where the asteroids are broken. Marc Kuchner, an Astrophysicist at the Goddard Space Flight Center and the Project Lead of Backyard Worlds: Planet 9, praised the efforts of citizen scientists and said,

“We built Backyard Worlds: Planet 9 mostly to search for brown dwarfs and new planets in the solar system. But working with citizen scientists always leads to surprises. Now that we’ve rebooted the website with double the amount of WISE data, we’re looking forward to even more exciting discoveries.”