Astronomers think they’ve discovered a black hole some 20 million times the mass of the Sun speeding away from the core of a distant galaxy. And as the supermassive black hole barrels through intergalactic space, it’s compressing the scant gas and dust available out there, leaving behind a thin line of newly formed stars that's some 200,000 light-years long.
"We think we're seeing a wake behind the black hole where the gas cools and is able to form stars," said Pieter van Dokkum of Yale University, who first identified the star trail, in a NASA release. "What we're seeing is the aftermath. Like the wake behind a ship, we're seeing the wake behind the black hole."
Despite being relatively thin, the black hole’s stellar wake is packed with plenty of hot blue stars, making it nearly half as bright as the parent galaxy it traces back to. Based on the available evidence, the researchers think this black hole was likely ejected during a complex dance between three supermassive black holes that were involved in a pair of galaxy mergers. If confirmed, this would be the first observational evidence showing that supermassive black holes can be ejected from their parent galaxies.
A paper detailing the candidate runaway black hole and its stellar wake was published April 6 in The Astrophysical Journal Letters.
Not so invisible after all
Although black holes themselves do not emit light, they often leave behind visible traces of their existence. For instance, many black holes are surrounded by dense disks of swirling, superheated gas and dust. Such accretion disks do emit copious light, making a black hole’s presence clearly known.