Just like a caught lover running out without their clothes, astronomers have spotted a supermassive black hole escaping a galaxy that's trailing behind its belongings, in this case all the stars that were once orbiting it.
Astronomers using the Very Long Baseline Array (VLBA) in Hawaii spotted B3 1715+425 – a black hole inside a tiny remnant galaxy – that is escaping a larger galaxy called ZwCl 8193. The galaxy has lost most of its gas and dust, leaving the black hole almost naked and moving at more than 2,000 kilometers (1,200 miles) per second. The findings are published in the Astrophysical Journal (with a pre-print available on arXiv).
"We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger," said lead author James Condon of the National Radio Astronomy Observatory in a statement. "Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it. We've not seen anything like this before."
Artist's impression of the nearly naked black hole forming. Bill Saxton, NRAO/AUI/NSF.
The system is part of a galaxy cluster 2 billion light-years from the Milky Way. It was picked up because of its unusual spectrum, and analysis has shown it to be a fast-moving galaxy 3,000 light-years in diameter. An average galaxy like the Milky Way is 100,000 light-years across.
Based on the mass and how the black hole is moving, the astronomers believe that the most likely scenario is that a formerly normal galaxy fell into ZwCl 8193, and it was stripped of most of its dust, stars, and gas as it passed near the core of the giant galaxy.
B3 1715+425 and its dissolving galaxy are the last hints of this encounter. Still, the team think it hasn’t finished losing its stellar companions yet. This is why they describe it as a nearly naked black hole in their paper.
"In a billion years or so, it probably will be invisible," Condon added.
This discovery suggests that there might be wandering supermassive black holes speeding through the universe. More observations will help astronomers understand how unique B3 1715+425 is.