Researchers have found the closest known black hole to Earth and among the smallest ever found on record. It lies 1,500 light-years from us.

The newfound black hole that researchers call “the Unicorn” is among the smallest scientists have ever found and the closest one yet.

Scientists gave this nickname for two reasons. One is because the black hole is clearly one of a kind. And second, because it lies within the Milky Way in the constellation Monoceros – Greek for a ‘one-horned rhinoceros.’

“Because the system is so unique and so weird, you know, it definitely warranted the nickname of ‘the Unicorn,'” discovery team leader Tharindu Jayasinghe, an astronomy Ph.D. student at The Ohio State University, said in a new video the school made to explain the find. 

While black holes are rather common in the universe, as are their discoveries. But what makes this one unique is that it’s been so close to us, and yet we haven’t detected it.

The Unicorn is about three times the mass of our sun. That’s tiny for a black hole and scientists have discovered very few black holes of this mass. The black hole is 1,500 light-years away from us, inside the Milky Way galaxy.

Reportedly, scientists never paid much attention to it because they didn’t think a black hole could be so small. Black holes typically are at least five times the mass of the sun.

“When we looked at the data, this black hole — the Unicorn — just popped out,” Tharindu Jayasinghe, who is pursuing his Ph.D. from the department of astronomy at the Ohio State University in the U.S., and led the study, told the press.

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What’s more interesting is that the Unicorn has a companion — a swollen red giant star that’s nearing the end of its life. Our sun will swell up, too, as a red giant in about five billion years. The researchers observed the Unicorn using a variety of instruments over the years, including the All-Sky Automated Survey and NASA’s Transiting Exoplanet Survey Satellite.

We can’t really see a black hole as they are pretty dark, not only visually but to the instruments astronomers use to measure light and other wavelengths. But in this case, scientists detected its companion star. That star had been well-documented by telescope systems including KELT, run out of Ohio State; ASAS, the precursor to ASAS-SN, which is now run out of Ohio State, and TESS, a NASA satellite that looks for exoplanets. Data about it had been widely available but hadn’t yet been analyzed in this way.

So, scientists analyzed all that data and noticed that the light of the red giant star shifts in intensity periodically. Thus, suggesting that another object is tugging on the star and changing its shape.

That pulling effect, called a tidal disruption, offers astronomers a signal that something is affecting the star.

Based on the velocity of the red giant, its orbital period, and the gravitational pull it appeared to be experiencing, the researchers concluded it could be a black hole — one harboring a mere three solar masses. For comparison, the supermassive black hole at the heart of our Milky Way galaxy packs about 4.3 million solar masses.

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That tidal disruption is produced by the tidal force of an unseen companion—a black hole.

“Just as the moon’s gravity distorts the Earth’s oceans, causing the seas to bulge toward and away from the moon, producing high tides, so does the black hole distort the star into a football-like shape with one axis longer than the other,” study co-author Todd Thompson, chair of Ohio State’s astronomy department, said in a statement. “The simplest explanation is that it’s a black hole — and in this case, the simplest explanation is the most likely one.”

Scientists have been wondering for quite a while now whether their methods of finding these black holes weren’t sophisticated enough, or they simply didn’t exist!?

Then, about 18 months ago, an Ohio State research team, led by Todd Thompson, published a scientific article in the journal Science, offering strong evidence that such black holes existed. That discovery motivated Jayasinghe and others, both at Ohio State and around the world, to search for smaller black holes. And that evaluation led them to the Unicorn.

Finding and analyzing black holes and neutron stars in our galaxy is crucial for studying space. That’s because it tells them about the way stars form and die.

Until now, astronomers have found very few super-lightweight black holes, because they’re pretty hard to find. As you know, black holes gobble up everything around them, including light. So scientists have looked for the impact they have on their surroundings. And the smaller the black hole, the smaller the impact.

Jayasinghe and his team published their findings on April 21, in the journal Monthly Notices of the Royal Astronomical Society. You can read it for free at the online preprint site

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