Astronomers apparently found the most famous black hole to Earth, a strange little object called ‘The Unicorn’ that is only 1,500 light-years away from us.
The nickname has a double meaning. Not only does the black-hole candidate live in the constellation Monoceros (“the unicorn”), its incredibly low mass – about three times that of the sun – makes it almost one of a kind.
“Because the system is so unique and so strange, you know, it certainly justified the nickname ‘The Unicorn’,” said discovery team leader Tharindu Jayasinghe, an astronomer Ph.D. student at Ohio State University, has in a new video made the school to explain the find.
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“The Unicorn” has a companion – an inflated red giant star it is nearing the end of his life. (Our sun will swell like a red giant over five billion years.) The companion has been observed over the years by a variety of instruments, including the All Sky Automated Survey and the Transiting Exoplanet Survey Satellite.
Jayasinghe and his colleagues analyzed the large data set and noticed something interesting: the red giant’s light shifts from time to time, indicating that another object is pulling at the star and changing its shape.
The team determined that the object that was pulling was probably a black hole – one that contained only three solar masses, based on details of the star’s velocity 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 distorts the Earth’s oceans, causing the seas to bulge to and from the moon and produce high tides. , “studied co-author Todd Thompson, chair of the Ohio Department of Astronomy, 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.”
The statement, probably though, was not set in stone; ‘The Unicorn’ currently remains a black hole candidate.
Very few such super lightweight black holes are known because they are incredibly hard to find. Black holes are known to include 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 black holes with an extremely low mass have increased significantly over the past few years, Thompson said, so that we could soon learn a lot more about these mysterious objects.
‘I think the field is moving here, to really map out how many low-mass, how many intermediate-mass and how many high-mass black holes there are, because every time you find one, it gives you a idea of which stars are collapsing, which is exploding and which is in between, ”he said in the statement.
Jayasinghe and his team report the discovery 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 website arXiv.org.
Mike Wall is the author of “Out there“(Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.