Stars can get in pretty peculiar configurations, which are often difficult to spot and even more difficult to model. But system TIC 168789840 truly is almost too extraordinary to be described. It is the first six-star system discovered where each pair of stars are eclipsing binaries.
Each star in the three pairings – A, B, and C – orbit each other in a matter of days. So, from the point of view of our planet, some of the stars in the system get covered partially by their companion. If this was not already exciting, the A and C systems orbit each other every four years. And those two systems orbit the B system every 2,000 years. A truly incredible stellar dance.
The study is accepted for publication in The Astronomical Journal. The team describes how this system is similar to Castor, the second brightest object in the Gemini constellation. Castor is also a six-star system, but only one pair in the Castor system eclipses from our point of view.
Another difference is just how similar the pairs in TIC 168789840 (also known by the equally catchy TYC 7037-89-1) are. They could be truly seen as triplets. And researchers believe that this is a crucial clue for how the system might have formed and evolved.
“In this work, we have presented the discovery of the first known sextuply-eclipsing sextuple star system TIC 168789840,” the international team wrote in the paper, which is available on the ArXiv.
“TIC 168789840 is a fascinating system that naturally merits additional observation and analysis. Though quite similar to the famous Castor system, the “triplet” nature of TIC 168789840 combined with the presence of three primary and three secondary eclipses enable further investigations into its stellar formation and evolution.”
The team put forward the possibility that star A and C form as a binary with a thick disk of material around them. They eventually encountered star B, which is captured on a wider orbit. All this excitement caused the collapse of gas in the disk into smaller companions, orbiting on roughly the same plane. It is a compelling hypothesis, but without more data, it remains highly speculative.
The discovery of this system is thanks to NASA’s Transiting Exoplanet Survey Satellite (TESS). TESS is keeping an eye on millions of stars and studying about 200,000 in detail. The team was able to use a machine-learning algorithm to find eclipsing binaries among 80 million stars. Among these, at least 100 were identified to be in systems with more than three stars.
TIC 168789840 is located 1,900 light-years away in the constellation Eridanus, a southern sky constellation named after the Latin name of Italy’s longest river.
[h/t: The New York Times]