First Triple Black Hole system discovered

Science: Astronomers have discovered the first “black hole triple” system, exploring the system that contains a black hole that is hungrily devouring a companion star while being orbited by a more distant, cautious star. Black holes form during the violent deaths of massive stars in supernova explosions, but this surprising discovery may indicate a more benign black hole birth process called “direct collapse.” That’s because if this black hole had a more violent origin, it would have provided a “pre-natal kick” that would have ejected the loosely bound distant star from this triple star system.

The system in question is V404 Cygni, located within the Milky Way and about 8,000 light-years from Earth. This so-called “X-ray binary” of a black hole and its victim star was already known, and the system has been well-studied. However, closer investigation by a team led by Kevin Burdge of the Massachusetts Institute of Technology (MIT) revealed that this binary actually lies at the center of a triple star system. Scientists believe most black holes form from violent explosions of stars, but this discovery helps call this into question.

“This system is very exciting for black hole evolution, and it also raises the question of whether there are more triples out there,” Burdge told Space.com via email. “The fact that this star is still bound is surprising because it means it received a low-energy natal shock.

“Overall, it is not surprising that black holes should be in triplets because a large proportion of massive stars are in triplets, but what is surprising is that this system maintained the triplet after the black hole was formed.” The team found that while this black hole’s “victim star” orbits it in just 6.5 Earth days, the newly discovered third star in the system orbits the greedy cosmic titan so far away that it completes an orbit only once every 70,000 Earth years.