A team of astronomers announces the discovery of a new sextuple star system (composed of six gravitationally bound stars) regularly eclipsing each other from Earth's point of view.
A black hole tearing apart a star, an exploding comet… the Transiting Exoplanet Survey Satellite (TESS) has spotted its share of surprises since its commissioning two years ago . This instrument, supposed to unearth new nearby exoplanets, this time reveals an intriguing new system made up of six stars:TC 168789840.
Found about 1900 light years away of the Earth, these objects merge into a single luminous point. Luckily, however, all evolve on a plane perfectly aligned with the Earth. In other words, each time one of these stars crosses another, it creates an eclipse visible from our planet. From a different point of view, this sixfold system would go completely unnoticed.
In their article published on the arXiv database (not yet peer-reviewed), the astronomers point out that this is not the first six-star system discovered. To date, three other such systems have indeed been isolated . The best known remains Castor (Constellation Gemini), one of the brightest "stars" in the night sky found 51 light-years from Earth.
Castor was first identified as a binary system (two stars) in 1719 by English clergyman and astronomer James Pound. Then, in 1905, astronomers realized that these two points were actually two pairs of stars orbiting each other and encircling a common center. Finally, in 1920, another team spotted a third pair of stars encircling the inner four, making it a six-star system.
These systems can also be organized in other ways. ADS 9731, another structure of the same kind, incorporates four light points surrounding a common center. Two of these bright spots are tight binaries, again making this a sixfold system.
"ICT 168789840 is on the other hand very similar to the famous Castor system “, write the authors. It consists of two inner pairs of stars that each spin in tight circles. In the first pair, the two stars rotate around every 31 hours and in the second every 38 hours. These two binaries, the "inner quadruple", also complete a circuit around a common center approximately once every 3.7 years.
Then two more "outer" stars orbit once every 197 hours and complete a full-system revolution once every 2000 years or so.
The presence of exoplanets within the system has not yet been confirmed, but if you lived on such worlds, "the night sky would be very special “, according to Tamás Borkovits, an astronomer at the Baja Astronomical Observatory in Hungary and co-author of the study. All inhabitants of these worlds "could see two suns, much like Luke Skywalker on Tatooine, along with four other very bright stars dancing around “.
Note that only one of these three pairs of stars could potentially have planets. The two inner binaries indeed rotate too very close to each other, forming their own quadruple subsystem. Planets formed in this environment would likely be ejected or engulfed by one of the four stars. The third more distant binary could on the other hand be a possible exoplanetary refuge according to the astronomer.
Researchers still do not yet know precisely how these complex multistar systems form. This new discovery offers essential data to try to solve this problem. In the future, TESS may also unearth others, providing us with other pieces of these complex puzzles.
