The black hole is the closest to Earth, one of the smallest ever discovered

Scientists have discovered one of the smallest black holes ever – and the closest to Earth found yet.

Researchers have named it ‘The Unicorn’, partly because it is unique so far, and partly because it was found in the constellation Monoceros – ‘The Unicorn’. The findings are published in the journal today, April 21 Monthly Communications from the Royal Astronomical Society.

“When we looked at the data, this black hole – the Unicorn – just emerged,” said lead author Tharindu Jayasinghe, a graduate student of astronomy at Ohio State University and an Ohio State presidential fellow.

The Unicorn is about three times the mass of our sun – small for a black hole. Very few black holes of this mass have been found in the Universe. This black hole is 1,500 light-years from Earth, still in the Milky Way. And until Jayasinghe started analyzing it, it was essentially hidden in plain sight.

The black hole appears to be a companion of a red giant star, meaning the two are linked by gravity. Scientists cannot see the black hole – they are dark by definition, not only visually, but also to the tools that astronomers use to measure light and other wavelengths.

But in this case, they can see the black hole’s companion star. That star was well documented by telescope systems, including KELT, which was outside the state of Ohio; ASAS, the precursor to ASAS-SN, now from the state of Ohio, and TESS, a NASA satellite that searches for planets outside our solar system. Data on it was generally available, but had not yet been analyzed in this way.

When Jayasinghe and the other researchers analyzed that data, they noticed that something they couldn’t see seemed to orbit the red giant, changing the light from that star in intensity and appearance at various points in its orbit.

Something, they realized, was pulling the red giant and changing shape. That migratory effect, called a tidal deformation, signals astronomers that there is something to do with the star. One option was a black hole, but it should be small – less than five times the mass of our sun, and fall into a large window that astronomers call the ‘mass gap’. Only recently have astronomers considered it a possibility that black holes of that mass could exist.

“If you look differently, and that’s what we do, you come across different things,” said Kris Stanek, study co-author, professor of astronomy at Ohio State and leading university scholar. Tharindu looked at this thing that so many other people had looked at and instead of ruling out the possibility that it could be a black hole, he said, ‘Well, what if it could be a black hole?’

That tidal disturbance is caused by the tidal force of an invisible companion – a black hole.

“Just as the moon’s gravity warps the Earth’s oceans, swelling the seas towards and away from the moon and producing high tides, so the black hole warps the star into a football-like shape with one axis longer than the other” , said Todd Thompson, study co-author, chair of Ohio State’s department of astronomy and leading university scholar. “The simplest explanation is that it is a black hole – and in this case, the simplest explanation is the most likely.”

The speed of the red giant, the period of its orbit, and the way the tidal force deformed the red giant told them the mass of the black hole, leading them to conclude that this black hole was about three times the mass of the Sun, or three times that of the red giant. Sun.

For about the past decade, astronomers and astrophysicists have been wondering if they didn’t find these black holes, because the systems and approaches they used weren’t sophisticated enough to find them. Or, they wondered, did they just not exist?

Then, about 18 months ago, many of the members of this Ohio state research team, led by Thompson, published a scientific article in the journal Science, with strong evidence that these types of black holes exist. That discovery motivated Jayasinghe and others, both in the state of Ohio and around the world, to seriously search for smaller black holes. And that evaluation led them to the Unicorn.

Finding and studying black holes and neutron stars in our galaxy is crucial for scientists studying space, as it tells them about how stars form and die.

But finding and studying black holes is almost by definition difficult: individual black holes don’t emit the same kind of rays as other objects in space. For scientific equipment, they are electromagnetically silent and obscure. Most of the known black holes were discovered because they interacted with a companion star, which generated a lot of X-rays – and those X-rays are visible to astronomers.

More large-scale experiments to try to locate smaller black holes have been launched in recent years, and Thompson said he expects more “mass gap” black holes to be discovered in the future.

“I think the field is pushing here, to really map out how much low mass, how much intermediate mass, and how much high mass black holes there are, because every time you find one, you get a sense of what stars are collapsing, which explode and those in between, ”he said.

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