Astronomers report the discovery of a record-breaking pair of ultracool brown dwarfs. Brown dwarfs are small stellar objects that were never massive enough to become full-fledged stars and, among them, the ultracold ones are failed stars that have a temperature just above the boiling point of the water. The LP 413-53AB pair breaks records in two respects. They are the oldest known pair and revolve around each other in 20.5 hours.
It is important to discuss a few things about these stellar objects to appreciate how different this pair is. Prior to LP 413-53AB, there were three other known pairs of ultracold dwarfs. All three were very young. At most, they were 40 million years old. It is childhood in cosmic terms. This newly discovered pair is billions of years old. And the stars have an orbital period at least three times shorter than that of all other ultracold dwarf binaries.
“It’s exciting to find such an extreme system,” Chih-Chun “Dino” Hsu, the Northwestern astrophysicist who led the study, said in a statement. “In principle, we knew that these systems should exist, but none of these systems had yet been identified.”
The two brown dwarfs are separated by less than one percent of the distance between Earth and the Sun. Image Credit: Adam Burgasser/University of California San Diego
The discovery of the system’s existence came from archival data based on an algorithm developed by Hsu. Then the pair was followed by observations using the WM Keck Observatory. And it is thanks to these observations that the team appreciated the speed with which these two brown dwarfs revolved around each other.
“When we were doing this measurement, we could see things changing within minutes of observation,” added co-author Professor Adam Burgasser of UC San Diego. “Most of the binaries we track have orbit periods of years. So you get a measurement every few months. Then after a while you can put the puzzle back together. With this system we could see the spectral lines deviate in real time. It’s amazing to see anything happening in the universe on a human scale.
Size and distance comparison of two brown dwarfs. Image Credit: Adam Burgasser/University of California San Diego
Brown dwarfs cool and shrink as they age, so turning the clock back means the stars were literally on top of each other if they stayed in their current position. The team thinks these two stars either migrated inward as they evolved, or maybe they had fun ejecting a third star.
There is a lot of interest in these particular systems, and researchers are hoping to discover many more.
“These systems are rare,” said Chris Theissen, study co-author and Chancellor’s postdoctoral fellow at UC San Diego. “But we don’t know if they’re rare because they rarely exist or because we just can’t find them. It’s an open question. We now have a data point that we can start building on. This data had remained in the archives for a long time. Dino’s tool will allow us to search for other binaries like this. »
Hsu will present this research at a press briefing at the 241st meeting of the American Astronomical Society in Seattle.