Scientists say a “runaway” black hole hurtling through the universe is unlike anything ever seen before.
The object first appeared as “scratches” on images from NASA’s Hubble Space Telescope.
But scientists now believe it is a black hole, which was ejected from its home galaxy and ripped apart the universe, leaving a trail of stars in its wake.
We think we are witnessing a wake behind the black hole as gas cools and is capable of forming stars. “We’re looking at the formation of stars that follow the black hole,” said Peter van Dokkum of Yale University.
“What we see are the consequences. Like a vigil behind a ship we watch beyond a black hole.”
Professor Van Dokkum spotted the accidental discovery in images from the Hubble telescope and documented it in a new paper, ‘A runaway black hole identified by shocks and star formation in its awakening’, published in 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 the Earth and the Moon in 14 minutes. Behind it is a trail of stars that stretches 200,000 light-years across, twice the width of our Milky Way galaxy.
These stars are thought to have formed when the black hole blasted through space, squeezing gas that then condensed and made the stars. Scientists think this happens because the black hole is moving so fast through this gas that it slams into it — but they still don’t know exactly how that works.
This unique phenomenon was spotted by chance when Professor Van Dokkum was searching for globular star clusters in a nearby dwarf galaxy. Instead, he saw what appeared to be artifacts on the photos, and said it was “pure coincidence that we stumbled upon them.”
“I was just scanning through the Hubble image and then I noticed we had a little line. I immediately thought, “Oh, a cosmic ray hitting the camera detector and causing a linear imaging artifact.”
When we removed the cosmic rays we realized they were still there. It didn’t look like anything we’d seen before.”
The runaway black hole likely formed from a group of black holes colliding together over time. The first two galaxies most likely formed when two galaxies merged about 50 million years ago, with two supermassive black holes at their center, then orbiting each other.
Then another galaxy joined with its own supermassive black hole. This destabilized the partnership and one of them may have been thrown into space, though scientists don’t know which.
Scientists hope to confirm this story using follow-up observations, investigating whether the object is indeed a black hole and how it might have formed.
If this can be confirmed, it would be the first time a black hole has been confirmed to have exited their home galaxy. This phenomenon was predicted decades ago.
“Nothing like this has ever been seen anywhere in the universe,” said Professor van Dokkum.
“We have long known that supermassive black holes exist, and it was predicted about 50 years ago that they can sometimes be ejected from galaxies. If confirmed, this would be the first evidence of a runaway supermassive black hole, validating this prediction.” .
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