new six-star system discovered

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A team of astronomers announces the discovery of a new six-fold star system (therefore composed of six gravitationally linked stars) regularly eclipsing each other from the point of view of the Earth.

A black hole tearing apart a star, a exploding comet… The Transiting Exoplanet Survey Satellite (TESS) has spotted its share of surprises since its entry into service two years ago. This instrument, supposed to find new nearby exoplanets, this time reveals a new intriguing system composed of six stars: TC 168789840.

Found around 1900 light years of the Earth, these objects merge into a single point of light. Luckily, however, all of them operate on a plane perfectly aligned with 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.

Rare systems

In their article published on the database arXiv (not yet peer reviewed), astronomers point out that this is not the first six-star system discovered. Nowadays, three other systems of this kind have in fact been isolated. The best known remains Castor (Constellation Gemini), one of the brightest “stars” in the night sky found in 51 light years from Earth.

Castor was first identified as a binary system (two stars) in 1719 by the English pastor and astronomer James Pound. Then, in 1905, astronomers realized that these two points were in fact two pairs of stars orbiting each other and encircling a common center. Finally, in 1920, another team spotted a third pair of stars circling the inner four, making it a six-star system.

These systems can also be organized differently. ADS 9731, another similar structure, incorporates four light points surrounding a common center. Two of those bright spots are tight binaries, again making this a sixfold system.

TIC 168789840 is on the other hand very similar to the famous Castor system“, Write the authors. It is made up of two internal pairs of stars that each rotate in tight circles. In the first pair, the two stars turn 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 about once every 3.7 years.

Then, two more more “outer” stars revolve around once every 197 hours and complete one revolution of the whole system once every 2000 years or so.

Illustration of the complex orbits of the Castor system. The newly discovered system has a similar structure. Credit: NASA / JPL-Caltech

A “very special” night sky

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, astronomer at the Baja Astronomical Observatory in Hungary and co-author of the study. All the inhabitants of these worlds “could see two suns, just like Luke Skywalker on Tatooine, as well as 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 are in fact rotating too very close to each other, forming their own quadruple subsystem. Planets formed in this environment would likely be ejected or swallowed up by one of the four stars. The third most 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 more, delivering us more pieces of these complex puzzles.

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