A new study has discovered a black hole roughly 1500 light years from Earth, the closest such object on record.
The dormant black hole, known as Gaia BH1, is 10 times as massive as the mass of the sun and is orbited by a Sun-like star. BH1 was identified using the European Space Agency’s Gaia spacecraft, and it and its stellar companion can be found in the night sky in the constellation Ophiuchus.
“This is the nearest known black hole by a factor of three, and its discovery suggests the existence of a sizable population of dormant black holes in binaries,” Dr. Kareem El-Badry, an astrophysicist at the Max Planck Center for Astronomy and the primary author of the paper outlining the discovery, said in a press release.
Black holes are superdense concentrations of matter that exert a gravitational force so strong that not even light can escape it. Because of that, they are often difficult to spot: Albert Einstein posited their existence as early as 1916, alongside his theory of general relativity, but they remained purely theoretical until astronomers discovered the first observed black hole, Cygnus X-1, in 1964.
Because they emit no light, astronomers rely on a black hole’s gravitational influence on other nearby celestial bodies to observe them. Black holes can consume nearby stars and nebulae — ripping them apart in a bright and violent spectacle before their mass passes the black hole’s ‘event horizon’, the point where its gravity becomes so strong that light can no longer escape.
Gaia BH1 is considered ‘dormant’ because it is not consuming anything at the moment — its stellar companion seems to be in a stable orbit outside the event horizon.
“I’ve been searching for dormant black holes for the last four years using a wide range of datasets and methods,” said El-Badry. “My previous attempts — as well as those of others — turned up a menagerie of binary systems that masquerade as black holes, but this is the first time the search has borne fruit.”
Scientists have observed 20 black holes within the Milky Way Galaxy, but, because of how difficult it is for most ‘dormant’ black holes to be identified, scientists believe the true number is much higher. Astronomers believe there could be 100 million black holes in our galaxy alone.
Black holes form during the collapse of exceptionally large stars (>8 solar masses). Stars form when accretions of gas are massive enough that the heat and pressure at their cores is high enough to cause nuclear fusion, which transforms lighter elements such as hydrogen and helium into heavier elements, with high mass stars being able to produce every element up to and including iron via such fusion. A star ‘survives’ so long as the energy and internal pressure produced by its core can counterbalance the pull of its own gravity.
Conventional fusion can only go so far and last for so long, however — even high mass stars can only fuse elements up to iron. Once a star has exhausted the fuel in it collapses into itself and ‘dies.’ The outer layers of the star are expelled in a massive explosion called a supernova — which produces minute amounts of heavy elements like gold, lead and uranium — and form new stellar nebulae that will coalesce into the next generation of stars. The remnant of the core condenses into a super dense form until a new force counterbalances the force of gravity: a star the size of our Sun would become a ‘white dwarf’, while more massive stars would collapse into ‘neutron stars’.
A black hole only forms when the force of gravity is so strong that no other force can counter it.
Another supermassive black hole, Sagittarius A*, sits at the center of our galaxy and is thought to be more than 4 million times as massive as the Sun, and astronomers believe that similar black holes lie at the core of nearly all large galaxies. With the breakthrough discovery of Gaia BH1, it is quite possible that we will find many smaller black holes in our local neighborhood.