Astronomers have apparently found the most famous black hole to Earth, a strange little object called “The Unicorn” lurking just 1,500 light-years from us.
The nickname has a double meaning. Not only does the candidate of the black hole reside in the constellation Monoceros (‘the unicorn’), its incredibly low mass – about three times that of the sun – makes it almost unique.
“Because the system is so unique and so weird, you know, it certainly earned the nickname ‘The Unicorn,’” ”research team leader Tharindu Jayasinghe, an astronomy Ph.D. student at Ohio State University, said in a statement. new video the school did to explain the find.
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“The Unicorn” has a companion – one blown up red giant star that is nearing the end of his life. (Our sun will swell like a red giant in about five billion years.) That companion has been observed by several instruments over the years, including NASA’s All Sky Automated Survey and NASA’s Transiting Exoplanet Survey Satellite.
Jayasinghe and his colleagues analyzed that large data set and noticed something interesting: The red giant’s light periodically changes in intensity, suggesting that another object is pulling the star and changing its shape.
The team determined that the object that is pulling is likely a black hole – one with only three solar masses, based on details of the star’s speed and light distortion. (For perspective, the supermassive black hole at the heart of our Milky Way Galaxy contains about 4.3 million solar masses.)
“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” study co-author Todd Thompson, president of the Ohio State Astronomy Department, said in a statement. “The simplest explanation is that it is a black hole – and in this case, the simplest explanation is the most likely.”
That explanation, however likely, is not set in stone; “The Unicorn” currently remains a candidate for a black hole.
Very few such superlight black holes are known because they are incredibly difficult to find. Black holes gobble up everything, including light, so astronomers have traditionally detected them by noting the impact they have on their environment (although we recently first direct image of a black hole, thanks to the Event Horizon Telescope). And the smaller the black hole, the smaller the impact.
But efforts to find extremely low-mass black holes have increased significantly in recent years, Thompson said, so we could learn a lot more about these mysterious objects soon.
“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 in the statement.
Jayasinghe and his team report the detection of “The Unicorn” in an article accepted for publication in the journal Monthly Notices of the Royal Astronomical Society. You can read it for free on the online preprint site arXiv.org.
Mike Wall is the author of “Outside(Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the quest for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.