For the first time in history, a team of international scientists discovered a dormant black hole outside the Milky Way. The new study published July 18 in the academic journal Nature Astronomy is based on observations from the European Southern Observatory’s (ESO) Very Large Telescope, in which researchers examine a binary system known as VFTS 243, some 160,000 light-years distant from Earth.
A binary system, made up of two stars revolving around each other, leaves behind an orbiting black hole with a luminous companion star. The black hole is “inactive” if it does not emit high levels of X-ray radiation, which is how these celestial objects are detected.
Located in the Large Magellanic Cloud, VFTS 243 is at least nine times the mass of our sun and orbits a hot blue star that weighs 25 times the mass of the sun, making it part of a binary system.
Although this was thought to be a fairly common cosmic phenomenon, according to the team of American and European researchers involved in the study, this is the first unequivocal detection of a dormant stellar-mass black hole outside the Milky Way.
In addition, the finding of the celestial object may also be extraordinary for another reason, since stellar-mass black holes typically form when massive stars run out of the fuel needed to continue nuclear fusion.
The end of the merger also ends the external pressure holding the star against complete gravitational collapse. The so-called core collapse that follows is often accompanied by a massive cosmic explosion called a “supernova,” which destroys the outer layers of the star.
However, the situation of the black hole in VFTS 243 appears to be different, with no visible traces of a supernova accompanying the collapse of the star. The team made the VFTS 243 find after six years of observations of nearly a thousand massive stars (each weighing at least eight times the mass of the Sun) in the Tarantula Nebula region of the Large Magellanic Cloud. in search of giant stars that could have a black hole as a companion. With VFTS 243, they found what they were looking for.
But, according to the study, identifying these companions as black holes is extremely difficult, since there are many alternative possibilities, so according to Tomer Shenar, co-author of the study, “We found a needle in a haystack” due to a process elimination.
First, the researchers identified stars that were part of binary systems. Subsequently, they searched for binary systems where the companion was not visible, and only then careful analysis revealed that VFTS 243 was a dormant black hole.