Astronomers have sighted a supermassive black hole traveling through space that appears to have been ejected from its host galaxy.
Researchers observing the dwarf galaxy designated RCP 28, roughly 7.5 billion light years away from our solar system, noticed an aberrant streak of light via the Hubble telescope. The “streak” appears to be a collection of stars being dragged out of their home galaxy by the immense gravitational force of a black hole.
The “runaway” black hole is the first of its kind to be observed, and appears to have been ejected from its original galaxy.
“We found a thin line in a Hubble image that is pointing to the center of a galaxy,” Professor Pieter van Dokkum of Yale University, the lead author of the study, said. “From a detailed analysis of the feature, we inferred that we are seeing a very massive black hole that was ejected from the galaxy, leaving a trail of gas and newly formed stars in its wake.”
The “stellar tail” in its wake is 200,000 light-years long, twice the diameter of our Milky Way galaxy.
The black hole in question is believed to be 20 million times more massive than the Sun, and it is traveling away from RCP 28 at a rate of 3.5 million miles per hour, roughly 4,500 times the speed of sound.
Black holes are celestial bodies where matter has been condensed and concentrated to such an extent that even light cannot escape its gravitational pull — as such, black holes are almost impossible to observe directly, and are usually spotted via their effects on nearby stars and nebulae (clouds of interstellar gas).
Black holes form during the collapse of exceptionally large stars. During the process of a large supernova, the gravitational force at the core of the star becomes so intense that it overpowers the other fundamental forces (the strong nuclear force, the weak nuclear force, electromagnetism), allowing incredible amounts of matter to be compressed into an exceptionally small space: physicists estimate that a black hole with the mass of our sun would measure only 6km in diameter (for comparison, the Sun measures ~1,400,000 km in diameter, making the blackhole 343 quadrillion times as dense).
Physicists don’t understand exactly how supermassive black holes (which range from hundreds of thousands to billions of times more massive than the Sun) formed, but they are believed to play a crucial role in galaxy formation as virtually every observed galaxy has one at its core, which their various stellar systems orbit. It’s unclear how such a massive object could be dislodged from its position in the galactic core.
“The most likely scenario that explains everything we’ve seen is a slingshot, caused by a three-body interaction,” van Dokkum said. “When three similar-mass bodies gravitationally interact, the interaction does not lead to a stable configuration but usually to the formation of a binary and the ejection of the third body. … Ejected supermassive black holes had been predicted for 50 years but none have been unambiguously seen. Most theorists think that there should be many out there.”