Astrophysicists have discovered the closest and oldest ultracool dwarf binary every observed. This is described as the shortest-period, low-mass stellar binary system yet recorded.
The two stars take less than one Earth day to revolve around each other. This means each star’s “year” lasts just 20.5 hours.
The observation comes from Northwestern University and the University of California San Diego (UC San Diego). The newly discovered system, named LP 413-53AB. The two stars are ultracool dwarfs, a class of very low-mass stars. These stars are so cool that they emit their light primarily in the infrared, making them completely invisible to the human eye.
What is important about the discovery is that previous observations amount to only three short-period ultracool dwarf binary systems. Each of these are relatively young — up to 40 million years old.
In contrast, LP 413-53AB is estimated to be billions of years old and it has an orbital period that is at least three times shorter than all of the ultracool dwarf binaries discovered so far. The distance between the two stars is about one percent of the distance between the Earth and the sun.
The researchers discovered the strange binary system while exploring archival data. This came about through the development of an algorithm that can model a star based on its spectral data.
By analyzing the spectrum of light emitted from a star, astrophysicists can determine the star’s chemical composition, temperature, gravity and rotation. This analysis also shows the star’s motion as it moves toward and away from the observer, known as radial velocity.
The stars will either have migrated toward each other as they evolved, or they could have come together after the ejection of a third — now lost — stellar member. More observations are needed to test these ideas.
According to lead researcher Chih-Chun “Dino” Hsu: “It’s exciting to discover such an extreme system. In principle, we knew these systems should exist, but no such systems had been identified yet.”
The observations were made using the telescopes at the W.M. Keck Observatory, an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. The starts were detected when the telescopes were orientated toward the constellation Taurus.
When studying LP 413-53AB, Hsu noticed how when the stars were roughly aligned and their spectral lines overlapped. Initially it appeared that there was only one star. However, as the stars moved in their orbit, the spectral lines shifted in opposite directions, splitting into pairs in later spectral data. Hence, there were two stars locked into an incredibly tight binary.
The research was presented to the 241st Meeting of the American Astronomical Society in Seattle, U.S.
