The work of scientists from the European Southern Observatory (ESO) found evidence of the invisible object while examining its two companion stars from one of the modern telescopes at the La Silla observatory in Chile. Located in the constellation Telescopium, the system found is so close that, on a clear night, the stars can be seen without the need for long-sight shots.
In the middle of the study, they came across a third body by surprise. Checks on the spectrograph spanned months and determined what they presumed: it was a black hole. The closest to our Solar System.
With deeper analysis, they were also able to know that the invisible object has a mass at least four times greater than that of the sun. Two main classes of black holes are known: stellar mass, like this, which usually has between three and up to dozens of times the solar mass, while the supermassive they are monstrous and weigh up to billions of solar masses, and lie at the centers of most large galaxies (last year the image of one of them, located some 55 million light-years from distance).
The HR 6819 it had gone completely unnoticed because it does not interact violently with its surroundings. A somewhat particular detail, since most of the black holes perceived in the galaxy do and in that activity they release powerful X-rays that end up betraying them. In this case, it made its presence known by its gravitational attraction, which forces one of the stars to enter orbit.
Although there are many puzzles around its formation and evolution, we know that black holes have existed since the earliest days of a galaxy’s life. Those of stellar mass are formed when a star runs out of fuel in its core, collapses under its own weight and triggers a supernova explosion. If the crushed core contains more than three times the mass of the sun, no known force can stop it from collapsing into a black hole. Once born, it can grow by accumulating matter that falls into it, including gas removed from neighboring stars or other black holes. Its gravitational pull is so strong that nothing, not even light, can escape.
If the hypotheses are correct, many more stars in the Milky Way galaxy will have collapsed at the end of their lives, so HR 6819 could provide clues to other hidden, silent and invisible black holes in our vicinity. Perhaps millions of them.
For scientists, the novelty is “the tip of an iceberg” and, in fact, they have already focused their telescopes on a second system, called LB-1, which could also be triple and, although a little further from Earth, still quite close in astronomical terms.