Hubble catches a runaway black hole

This Hubble Space Telescope archival photo captures a curious linear feature that is so unusual it was first dismissed as an imaging artifact from Hubble's cameras. But follow-up spectroscopic observations reveal it is a 200,000-light-year-long chain of young blue stars. A supermassive black hole lies at the tip of the bridge at lower left. The black hole was ejected from the galaxy at upper right. It compressed gas in its wake to leave a long trail of young blue stars. Nothing like this has ever been seen before in the universe. This unusual event happened when the universe was approximately half its current age. Credits: NASA, ESA, Pieter van Dokkum (Yale); Image Processing: Joseph DePasquale (STScI)
This Hubble Space Telescope archival photo captures a curious linear feature that is so unusual it was first dismissed as an imaging artifact from Hubble's cameras. But follow-up spectroscopic observations reveal it is a 200,000-light-year-long chain of young blue stars. A supermassive black hole lies at the tip of the bridge at lower left. The black hole was ejected from the galaxy at upper right. It compressed gas in its wake to leave a long trail of young blue stars. Nothing like this has ever been seen before in the universe. This unusual event happened when the universe was approximately half its current age. Credits: NASA, ESA, Pieter van Dokkum (Yale); Image Processing: Joseph DePasquale (STScI)
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The Hubble Space Telescope has found evidence of a “runaway” black hole that was ejected from its host galaxy after a tussle between it and two other black holes. It’s moving so fast that if it was in our own solar system, it could travel from Earth to the Moon in 14 minutes!
This supermassive black hole weighs around 20 million Suns, and instead of devouring the stars in its path, it has left behind a 200,000-light-year-long trail of newborn stars, twice the diameter of our Milky Way Galaxy. Nothing like it has ever been seen before, but it was captured accidentally by NASA’s Hubble Space Telescope.
“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 star formation trailing the black hole,” said Pieter van Dokkum of Yale University in New Haven, Connecticut. “What we’re seeing is the aftermath. Like the wake behind a ship we’re seeing the wake behind the black hole.” The trail must have lots of new stars, given that it is almost half as bright as the host galaxy it is linked to.

According to NASA: “The black hole lies at one end of the column, which stretches back to its parent galaxy. There is a remarkably bright knot of ionized oxygen at the outermost tip of the column. Researchers believe gas is probably being shocked and heated from the motion of the black hole hitting the gas, or it could be radiation from an accretion disk around the black hole.”

“Gas in front of it gets shocked because of this supersonic, very high-velocity impact of the black hole moving through the gas. How it works exactly is not really known,” said van Dokkum.

“This is pure serendipity that we stumbled across it,” van Dokkum added. He was looking for globular star clusters in a nearby dwarf galaxy. “I was just scanning through the Hubble image 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 cosmic rays we realized it was still there. It didn’t look like anything we’ve seen before.”

The researchers decided to do follow-up spectrocopy with the W. M. Keck Observatories in Hawaii because the black hole seemed to strange and van Dokkum describes the star trail as “quite astonishing, very, very bright and very unusual.” These observations led him to conclude that he was looking at the aftermath of a black hole flying through a halo of gas surrounding the host galaxy.

It is most likely the aftermath of multiple collisions of supermassive black holes. It is possible that the first two galaxies merged around 50 million years ago and brought together two supermassive black holes at their centres, which then whirled around each other as a binary black hole. The another galaxy approached with its own supermassive black hole, which caused a “chaotic and unstable configuration”.

According to NASA:

“One of the black holes robbed momentum from the other two black holes and got thrown out of the host galaxy. The original binary may have remained intact, or the new interloper black hole may have replaced one of the two that were in the original binary, and kicked out the previous companion. When the single black hole took off in one direction, the binary black holes shot off in the opposite direction. There is a feature seen on the opposite side of the host galaxy that might be the runaway binary black hole. Circumstantial evidence for this is that there is no sign of an active black hole remaining at the galaxy’s core. The next step is to do follow-up observations with NASA’s James Webb Space Telescope and the Chandra X-ray Observatory to confirm the black hole explanation.”

 

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I am a Chartered Environmentalist from the Royal Society for the Environment, UK and co-owner of DoLocal Digital Marketing Agency Ltd, with a Master of Environmental Management from Yale University, an MBA in Finance, and a Bachelor of Science in Physics and Mathematics. I am passionate about science, history and environment and love to create content on these topics.

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