Astronomers Discover Closest Known Black Hole to Earth

Astronomers have discovered a black hole closer to Earth than any other previously found. It’s about ten times as massive as our sun and is located just 1,600 light-years away—rather nearby on a cosmic scale.

While scientists have only spotted about 20 black holes in the Milky Way to date, they estimate that some 100 million more are lurking in our galaxy, each between 5 and 100 times more massive than our sun.

With so many more undetected, the newly discovered black hole shouldn’t hold the title of “closest to Earth” forever, suggests their paper published last week in Monthly Notices of the Royal Astronomical Society.

“We think there are probably a lot that are closer,” Kareem El-Badry, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, says to Science News’ Lisa Grossman. “Just finding one… suggests there are a bunch more to be found.”

Most black holes are born from the deaths of large stars, according to NASA. When stars roughly ten times the mass of the sun or bigger reach the ends of their lives, they collapse in powerful supernova explosions. They leave behind the mass of at least several suns, tightly packed into a relatively small space: the black hole. These dense objects have incredibly strong gravitational pulls from which nothing, including light itself, can escape.

Since no light leaves a black hole, scientists cannot observe one directly. But as active black holes gobble up nearby material, they emit X-rays that point scientists to their existence, per the Times.

But dormant black holes, like the newly discovered one, are not feeding and therefore don’t emit X-rays. Though dormant black holes are more common, they can be harder to spot. But El-Badry and his colleagues found a hint to this one’s existence in data from the European Space Agency’s GAIA spacecraft, which tracks the positions and movements of stars in the Milky Way, per the Times.

The scientists noticed a star in the constellation Ophiuchus moving in unexpected ways, and they realized that the gravity of an unknown, massive object was to blame, according to a statement from the National Optical-Infrared Astronomy Research Laboratory (NOIRLab). The researchers then used observations from other telescopes, including one run by NOIRLab, to support the theory that this mystery object was a black hole.

Compared to the previously nearest-known black hole, this one is three times closer to Earth, per the statement.

Its nearby star is about the same size as our sun, and the two objects are roughly as far from each other as our sun and Earth are, per the Times. The researchers aren't sure why the star wasn’t consumed as its partner star expanded, died and formed the black hole.

“It poses many questions about how this binary system was formed, as well as how many of these dormant black holes there are out there,” El-Badry said in the statement.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.