A “runaway” black hole is shooting through the universe like never before, scientists say.
The object first appeared as a “scratch” in images from NASA’s Hubble Space Telescope.
But scientists now believe it is a black hole, ejected from its home galaxy and tearing through the cosmos, leaving a trail of stars in its wake.
“We think we’re seeing a wake behind the black hole where the gas cools and is able to form stars. So, we’re looking at the star formation behind the black hole,” said Peter van Dokkum of Yale University.
“What we’re seeing is the latter. We see wakes behind black holes, like wakes behind ships.”
Professor van Dokkum spotted the accidental discovery in images from the Hubble telescope and documented them in a new paper, ‘A candidate runaway supermassive black hole identified by shocks and star formation in its wake’, published Astrophysical Journal Letters.
The black hole weighs as much as 20 million suns and is traveling so fast that if it were in our solar system it would travel between Earth and the Moon in 14 minutes. Behind it lies a path of stars that spans 200,000 light-years, twice as wide as our Milky Way galaxy.
These stars are thought to form when black holes hurtle through space, compressing gas that then condenses to form stars. Scientists think this happens because the black hole is moving through that gas so fast that it pushes it – but still don’t know exactly how it works.
The entire unique phenomenon was discovered by accident when Professor van Dokkum was looking for globular star clusters in a nearby dwarf galaxy. Instead, he found that the images appeared to be artifacts, and said it was “pure serendipity that we stumbled upon it”.
“I was scanning through the Hubble images and then I noticed that we have a little streak. I immediately thought, ‘Oh, a cosmic ray hitting the camera detector and causing a linear imaging artifact.’
“When we eliminated the cosmic rays we realized it was still there. It doesn’t look like anything we’ve seen before.”
Runaway black holes were likely formed by a group of black holes that collided together over time. The first two probably formed when two galaxies collided about 50 million years ago, with two supermassive black holes at their centers, which then orbited each other.
Then another galaxy joins in, with its own supermassive black hole. This destabilized the partnership, and one of them was likely thrown into space, although scientists don’t know which one.
Scientists hope to confirm that story using follow-up observations to test whether the object is indeed a black hole and how it might have formed.
If confirmed, it would be the first time a black hole has been confirmed to be ejected from its home galaxy. Such an event has been predicted for decades.
“Something like this has never been seen anywhere in the universe,” said Professor van Dokkum.
“We’ve known for a long time that supermassive black holes exist and predicted for about 50 years that they could sometimes escape from galaxies. If confirmed, this prediction would be the first evidence of a runaway supermassive black hole.”