Astronomers have discovered a new black hole called “The Unicorn” that is both one of the smallest black holes on record and one of the closest to Earth. It has been dubbed The Unicorn in part because it was discovered in the constellation Monoceros (The Unicorn) and in part because it is one-of-a-kind. Researchers say when they looked at the data on the black hole, they found it’s about three times the mass of the sun.
That is very small for a black hole, and very few black holes of this mass have been discovered in the universe. On a cosmic scale, The Unicorn is also very close at 1500 light-years away, placing it inside the Milky Way galaxy. Researchers say the black hole appears to be a companion to a red giant star.
Scientists can’t see the black hole itself, but they can see its companion star, which has been well documented using multiple telescopes. Data about the red giant is widely available but hadn’t been analyzed in the way the researchers have. While analyzing the data, researchers on the team noticed something they couldn’t see appeared to be orbiting the red giant, causing the light from the start to change in intensity at various points of its orbit.
That pulling effect is called tidal distortion, and one option for the phenomenon is a black hole. Black holes less than five times the mass of our sun are part of a group that fall into a window called the “mass gap.” Researchers say just as the moon’s gravity distorts the oceans on Earth, producing high tides, the gravity of the black hole distorts the star into a football-like shape with one axis longer than the other.
Researchers say the simplest explanation for this is that a black hole is orbiting the star, and in this instance, the simplest explanation is the most likely one. Scientists were able to estimate the black hole’s mass based on the velocity of the red giant, the period of the orbit, and the way the tidal force distorts the star.