According to the team of astronomers and researchers, it's "forms part of a triple system that can be seen with the naked eye".
The presence of a hidden black hole in HR 6819 was discovered by researchers from the European Southern Observatory (ESO)'s La Silla Observatory in Chile. Based on the cosmic distance scale, one light-year equals about 6 trillion miles.
"We realised that one could not describe what we saw with just two stars", Dietrich Baade, an emeritus astronomer at European Southern Observatory (ESO) and a co-author of the study, was quoted as saying by Guardian. But he pointed out that the authors need to rely on an assumption in order to calculate the visible star's mass, and if that assumption is wrong, then the invisible object might be less massive-and potentially a neutron star or even a very light regular star, not a black hole at all. The second star is further out from the first star and the black hole. They found it hiding in a double-star system known as HR 6819, where scientists say the black hole - rendered effectively invisible by gravity so strong that even light can not escape - revealed itself in the curious orbit of the star nearer the center of the system.
This, combined with the fact that the body in question was four times as massive as the Sun, led the team to posit that it might be a black hole.
This wide-field view shows the region of the sky, in the constellation of Telescopium, where HR 6819 is located.
The new discovery has unseated the black hole found in system A0620-00, which is located more than 3,000 light-years away in the constellation Monoceros - and which for years was the nearest black hole to Earth that scientists had identified.
Astronomers have spotted only a couple of dozen black holes in our galaxy to date, almost all of which strongly interact with their environment and make their presence known by releasing powerful X-rays in this interaction.
For comparison, consider some of the best-known black holes in astronomy, the ones usually intriguing enough to make headlines. Astronomers theorise there are between 100 million to 1 billion of these small but dense objects in the Milky Way. This prompted us to resume our work on HR 6819 which confirmed the conclusion reached back in 2010 that this system consists of 2 luminous stars and one invisible object. As a result, the HR 6819 black hole remained "truly black", emitting no light or radiation, and was therefore invisible to direct detection by telescopes.
"An invisible object with a mass at least 4.2 times that of the Sun can only be a black hole", Dr. Rivinius said. "If their measurements are accurate", Markoff adds, the amount of missing mass for this unseen object "leaves no doubt that it is a black hole". "They have good evidence", says Todd Thompson, an astronomer at Ohio State University.
So, how, for a star so close by and easily spotted in the southern night sky, could a black hole have remained hidden there for so long?
"We shall try to obtain more observations to find and characterize more systems so that their commonalities can identify the patterns of their formation and evolution".
Astronomers have discovered a new black hole, and it is not really far away.