Two brown dwarfs spin around each other in record time
Researchers from Northwestern University and the University of California report the discovery of a pair of ultra-cool, very narrow brown dwarfs. The two "failed stars", which represent the oldest binary system known for this type of object, revolve around each other in less than one Earth day.
Brown dwarfs are too massive objects to be considered as planets , but too small to trigger thermonuclear fusion reactions that would make them real stars. These objects emit their light mainly in the infrared, which makes them completely invisible to the human eye. Among them are brown dwarfs that are "cooler" than the others (called ultra-cold) whose effective temperature is just above the boiling point of water.
That being said, like stars, brown dwarfs can evolve alone or in pairs. So far, there have only been three known pairs, all of which are at most 40 million years old . This newly discovered pair (named LP 413-53AB b) is therefore interesting insofar as these binary systems are quite rare, at least to our knowledge.
However, this system is intriguing for two other reasons. On the one hand, these two ultra-cold brown dwarfs are much older than the other three formed since they formed several billion years ago . On the other hand, the two objects revolve around each other in just 20.5 Earth hours , which is a record for this type of object. The other pairs indeed have orbital periods that are sometimes several years long.
1% of the Earth-Sun distance
The researchers isolated this binary system by mining archival data using a new algorithm capable of modeling a star based on its spectral data . By analyzing the spectrum of light, researchers can derive some essential information, such as the star's chemical composition, temperature or rotation. These analyzes also show the movement of a star as it approaches and moves away from the observer (radial velocity).
However, the data from this particular system was visibly strange. Initially, early observations captured the system when the stars were roughly aligned. Thus, their spectral lines overlapped . The researchers then thought that it was just one of a single star. Then, as the stars moved through their orbits, the spectral lines also split in opposite directions. At that point, the team figured out that they were actually two stars locked in a very tight binary.
Follow-up observations from the WM Keck Observatory in Hawaii confirmed these data, revealing in passing that the distance between the two brown dwarfs was about 1% of the Earth-Sun distance , which is about 150 million kilometers.
The two brown dwarfs are separated by less than one percent of the distance between Earth and the Sun. Credits: Adam Burgasser/University of California San Diego
With the usual binaries, researchers get a measurement every few months and can, over time, piece the puzzle together. With this system, they were able to observe the spectral lines deviating in real time. It is quite rare to be able to observe a phenomenon occurring in the universe on a human scale.
" It's exciting to find such an extreme system ," said astrophysicist Chih-Chun "Dino" Hsu, who initiated the study. “ In principle, we knew that these systems should exist, but none of these systems had yet been clearly identified. "
It is also worth noting that brown dwarfs shrink as they age. Thus, there was a time when these two objects were truly on top of each other if they were in their current position. However, the researchers rather believe that these two "failed stars" migrated inward as they evolved. It is also possible that they got closer after the ejection of a third star member. Follow-up observations will be needed to test these two hypotheses.
Source:websites