JUNE 19, 2018
Since their discovery, the only acknowledged black hole varieties represent two extremes: one could swallow the sun, and the other could swallow an entire galaxy. Scientists have long sought proof of mid-size black holes that could fill the gap, and now, they’re one step closer.
For the first time, a group of researchers captured an intermediate-mass black hole as it swallowed a star with satellite imaging, according to Nature Astronomy. Though several potential black holes of its size have been discovered, scientists believe it’s evidence of many more undiscovered middle-tier black holes laying dormant in the universe.
The astrophysicists found the flare using three X-ray telescopes on the edge of a remote galaxy. They determined the black hole consumed the star in 2003, and the flare’s brightness decayed over 10 years.
Scientists also identified the size of a black hole by the type of flare it emits. A long flare like the one created by an intermediate black hole reaches maximum luminosity, or a state of balance achieved when gravitational forces of the black hole pulling a star inward equal the radiation it extends outward. A black hole’s tidal forces can destroy stars that come too close to it, and as it consumes most of the stellar debris, the star’s remains heat up and create an X-ray flare unique to each type of black hole.
“From the theory of galaxy formation, we expect a lot of wandering intermediate-mass black holes in star clusters. But there are very, very few that we know of, because they are normally unbelievably quiet and very hard to detect and energy bursts from encountering stars being shredded happen so rarely,” lead author Dacheng Lin said in a statement.
Intermediate-mass black holes have been spotted multiple times, but astronomists said the evidence is inconclusive. In 2015, researchers found a candidate for the black hole variety that emitted ultraluminous X-ray light, a rarity for the middle-tier black hole. The light produced by stellar debris that falls in intermediate-mass black holes isn’t as bright as that produced by supermassive black holes, which makes them more difficult to locate.
“The ultimate way of finding and identifying intermediate-mass black holes is not by emission of light, but by the emission of gravitational waves,” astrophysicist Tal Alexander told Space.com.
Intermediate-mass black holes are thought to weight between 100 and 100,000 solar masses. If accepted by astrophysicists, they’d sit between stellar-mass black holes, which weigh five to 10 times the sun’s mass, and supermassive black holes, which can outweigh the sun by millions or billions.
The earliest black holes formed following the big bang, NASA said, while stellar black holes occur when a massive star’s center collapses in on itself, creating a supernova. Supermassive black holes are thought to have formed at the same time of the galaxy they exist in, which affects the size and mass of the black hole. The cause of intermediate-mass black holes is unknown, though scientists posit they formed as a result of collisions in the earliest star clusters.