Massive, exceptionally compact and ‘one of a kind’ triple star system detected for the first time

Earlier this year, scientists from the Niels Bohr Institute at the University of Copenhagen announced the discovery of an unusual star trio. The system discovered by them consists of two stars that orbit each other and a third, more massive star that orbits the pair. The research was published in the Monthly Notices of the Royal Astronomical Society in June.

“As far as we know, this is the first of its kind ever detected. We know of many tertiary star systems (three-star systems), but they are generally much less massive. The massive stars of this triplet are very close to the from each other – it’s a compact system,” said Alejandro Vigna-Gomez, corresponding author of the study and postdoctoral fellow at the Niels Bohr International Academy, in a press release.

The binary pair of two stars dancing around each other at the center of the system has a combined mass that is twelve times the mass of the sun. Binary also has an orbital period which is roughly the same length as a day on Earth. While the binary in the center may appear to be made of massive stars, the tertiary star is about 16 times the mass of our Sun, making it even more massive.

The system’s inner orbit is circular, with the tertiary star circling the binary pair nearly six times a year. It’s really fast when you consider the size of the stars in the system. The very bright system was first thought to be just a stellar binary when it was first detected.

But then a community of amateur astronomers discovered something a bit unusual while browsing through a public dataset from NASA’s Transiting Exoplanet Survey Satellite (TESS) observatory. They saw some anomalies in the detection and it turns out that what was initially thought to be two stars was actually three stars.

The researchers considered several possible explanations for how the system might have formed. And after more than 100,000 computer simulations, they came to the conclusion that there may have been two binary systems that formed initially before one of the binary systems merged to form the massive tertiary star.