Astrophysicists discover the most unusual ultracool dwarf binary system

The two stars take about 20.5 hours to revolve around each other.
Kavita Verma
An illustration of what a "Y dwarf" might look like.
An illustration of what a "Y dwarf" might look like.

NASA/JPL Caltech image 

Astrophysicists of the University of California San Diego (UC San Diego) and Northwestern University have discovered the most compact ultracool dwarf binary system known to date using W. M. Keck Observatory on Maunakea, Hawaii Island.   

These two stars are so close that they only take about 20.5 hours to revolve around each other, which means a year on these stars is not even a day on Earth.   

Astrophysicists discover the most unusual ultracool dwarf binary system
Illustration of the oldest known pair of ultracool dwarf stars that orbit each other so closely, they take less than one Earth day to revolve around each other.

Named LP 413-53AB, this newly discovered system comprises two ultracool dwarfs, the category of stars which are extremely low in mass and emit light mainly in the infrared because of their low temperature. These features make them completely invisible to the human eye, although they are the most common type of star in the cosmos. 

The unusual behavior of LP413-53AB 

In the past, only three short-period ultracool dwarf binary systems have been discovered by astronomers, and all of them were comparatively young — a maximum of 40 million years old. It is estimated that LP413-53AB is billions of years old — similar to our Sun. However, the system's orbital period is 1/3 of the other ultracool dwarf binaries discovered to date.     

The research was represented by Hsu in a press briefing at the 241st Meeting of the American Astronomical Society in Seattle. “Discovery of the shortest period ultracool dwarf binary” took place today (January 10) as part of a session on “Stars and Their Activity.” Members of the media can register here

This strange binary system was discovered by the team while analyzing archival data. An algorithm developed by Hsu can model a star on the basis of its spectral data. The chemical composition, temperature, gravity, and rotation of the star could be determined by observing the spectrum of light produced by a star. Through this analysis, the star’s motion as it moves towards or away from the observer could also be determined.   

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While examining the spectral data of LP413-53AB, Hsu observed something unusual. In early observations captured by the system, the stars were aligned roughly, and their spectral lines overlapped. Hence, Hsu believed it was just one star. However, when the stars moved in their individual orbits, their spectral lines were observed splitting into pairs, leading Hsu to realize that there were two stars arranged in an extremely tight binary. 

Chih-Chun “Dino” Hsu started this study as a Ph.D. student at UC San Diego, where he was guided by Professor Adam Burgasser.

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