Black hole discovered just 1,000 light years from Earth (Artist’s impression of the triple system with the closest black hole © ESO/L. Calçada)

Black hole discovered just 1,000 light years from Earth

Discovery of the closest black hole to our home planet suggests there could be many more out there, scientists explain.

European astronomers have found the closest black hole to Earth yet – so near that two stars orbiting it can be seen by the naked eye.

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Of course, close is relative on the galactic scale. This black hole is about 1,000 light-years away and each light-year is 9.46 trillion kilometres.

But in terms of the cosmos and even the Galaxy, it is nearby, said European Southern Observatory astronomer Thomas Rivinius, who led the study published in the journal Astronomy & Astrophysics.

The previous closest black hole is probably about three times further, about 3,200 light-years, he said.

The discovery of a closer black hole, which is in the constellation Telescopium in the Southern Hemisphere, hints that there are more out there. Astronomers theorise there are between 100 million to 1 billion of these small but dense objects in the Milky Way.

But scientists can usually only spot them when they’re absorbing sections of a partner star or another object falls into them.

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Astronomers believe most black holes, including this newly discovered one, do not have anything close enough to swallow. So they go undetected.

Astronomers found this hole because of the unusual orbit of a star. The new black hole is part of what used to be a three-star dance in a system called HR6819. The two remaining super-hot stars are not close enough to be sucked in, but the inner star’s orbit is warped.

This chart shows the location of the HR 6819 triple system, which includes the closest black hole to Earth, in the constellation of Telescopium. This map shows most of the stars visible to the unaided eye under good conditions and the system itself is marked with a red circle. While the black hole is invisible, the two stars in HR 6819 can be viewed from the southern hemisphere on a dark, clear night without binoculars or a telescope © ESO, IAU and Sky & Telescope
This chart shows the location of the HR 6819 triple system in the constellation of Telescopium © ESO, IAU and Sky & Telescope

Using a telescope in Chile, they confirmed that there was something about four or five times the mass of our Sun pulling on the inner star. It could only be a black hole, they concluded.

“It will motivate additional searches among bright, relatively nearby stars,” said Ohio State University astronomer Todd Thompson.

Like most of these type of black holes, this one is tiny, maybe 40km in diameter.

“Washington, DC would quite easily fit into the black hole, and once it went in it, would never come back,” said astronomer Dietrich Baade, a study co-author.

This wide-field view shows the region of the sky, in the constellation of Telescopium, where HR 6819 can be found, a triple system consisting of two stars and the closest black hole to Earth ever found. This view was created from images forming part of the Digitized Sky Survey 2. While the black hole is invisible, the two stars in HR 6819 can be viewed from the southern hemisphere on a dark, clear night without binoculars or a telescope © ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin
The region of the sky, in the constellation of Telescopium, where HR 6819 can be found © ESO/Digitized Sky Survey 2/Davide De Martin

These are young hot stars compared to our 4.6 billion-year-old Sun.

They are maybe 140 million years old, but at 15,000°C, they are three times hotter than the Sun, Dr Rivinius said.

About 15 million years ago, one of those stars got too big and too hot and went supernova, turning into the black hole in a violent process, he said.

“It is most likely that there are black holes much closer than this one,” said Avi Loeb, director of Harvard’s Black Hole Initiative.

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“If you find an ant while scanning a tiny fraction of your kitchen, you know there must be many more out there.”

Reader Q&A: Do black holes collapse?

Asked by: Patricia Rodrigues, King’s Lynn

The Schwarzschild radius (event horizon) of a black hole is sometimes thought of as the black hole’s ‘size’. It is proportional to mass, which means that more massive black holes have bigger Schwarzschild radii.

Left alone, black holes lose mass due to ‘Hawking radiation’, so that their event horizons are slowly shrinking. A typical black hole would take many billions of times the age of the Universe to completely ‘evaporate’ and disappear.

But, the interior of the black hole, or its ‘singularity’ (the point at which all the black hole’s matter is concentrated) has already reached the limit of its density and cannot ‘collapse’ any further.

Read more about black holes: