The closest black hole to Earth has been discovered just 1,000 light years away.
It is so close to us that on a clear night its stars can be seen with the naked eye.
The hole, located in the constellation Telescopium, forms part of a “triple system” with two accompanying stars.
It was discovered by astronomers from the European Southern Observatory (ESO) and other institutes and is closer to our solar system than any other recorded to date.
The team found evidence of the invisible object by tracking its two companion stars using a 2.2 metre telescope at ESO’s La Silla Observatory in Chile.
No telescope or binoculars are needed to see the stars on a dark, clear night from the southern hemisphere.
Research co-author Petr Hadrava, Emeritus Scientist at the Academy of Sciences of the Czech Republic in Prague, said: “We were totally surprised when we realised that this is the first stellar system with a black hole that can be seen with the unaided eye.”
The team originally observed the system, called HR 6819, as part of a study of double-star systems.
But on analysing their observations they were stunned to discover a third, previously undetected body – a black hole.
The findings show one of the two visible stars orbits an unseen object every 40 days while the second star keeps a large distance.
The hidden black hole in HR 6819 is one of the very first stellar-mass black holes – formed by the collapse of a star – that does not interact violently with its environment and therefore appears truly black.
But the team could spot its presence and calculate its mass by studying the orbit of the star in the inner pair.
Study leader and ESO scientist Dr Thomas Rivinius said: “This system contains the nearest black hole to Earth that we know of.
“An invisible object with a mass at least four times that of the Sun can only be a black hole.”
Now experts believe this triple system could lead to many more similar black holes being found in the future.
Astronomers have spotted only a couple of dozen black holes in our galaxy to date, nearly all of which strongly interact with their environment and make their presence known by releasing powerful X-rays.
Scientists estimate many more stars collapsed into black holes as they ended their lives over the Milky Way’s lifetime.
They say discovery of a silent and invisible black hole in HR 6819 provides clues about where these might be.
And astronomers believe the revelation could shine some light on a second system called LB-1 which may also be a triple.
Dr Rivinus said: “There must be hundreds of millions of black holes out there, but we know about only very few. Knowing what to look for should put us in a better position to find them.”
The study was published in the journal Astronomy & Astrophysics.