A black hole has a tail of stars

A team of researchers discovered through an image from the Hubble telescope a black hole expelled from a galaxy with a tail of stars

A supermassive black hole ejected from its own galaxy is followed by a tail of newly forming stars that extends 200,000 light-years. Incredible sight, unlike anything astronomers have ever seen before, was identified by the Hubble Space Telescope. The black hole, with a mass equivalent to 20 million suns, is traveling so fast through space that it would be able to cover the distance between Earth and the Moon in just 14 minutes.

The incredible discovery

As it travels through space, the black hole is accumulating gas in front of it. When dense regions of gas, like those left in its wake, collapse, new stars are born. Normally, a black hole of this size would feed on the clouds of gas it passes through via the accretion process. But this cosmic monster is moving too quickly to feed on gas.

The consequence is that the black hole is creating a tail of newly forming stars that extend back to its original galaxy, the researchers said. Furthermore, the tail is nearly as bright as the galaxy, which means it is rich in stars. “It’s simple serendipity” said lead author of the study (ref.) Pieter van Dokkum, of Yale University. “I was scanning the Hubble image when I noticed a small streak. I thought it was a cosmic ray that had hit the camera’s detector, creating a linear artifact. But when we eliminated the cosmic rays, we realized it was still there”.

The researcher continued in his statement, trying to explain what is seen in the image. “We think we’re seeing a tail behind the black hole where the gas cools and is able to form stars. So, we’re observing star formation following a black hole”. Without a doubt, it is extraordinary that the phenomenon had never been noticed before. “It didn’t look like anything we had seen before. The gas in front is heated due to the supersonic impact with the black hole moving through the gas” van Dokkum said. “Exactly how it works is unknown”.

This archive photo from the Hubble Space Telescope captures reveal that it is a chain of young blue stars 200,000 light years long.
This archive photo from the Hubble Space Telescope reveal that it is a chain of young blue stars 200,000 light years long. Credit: NASA

Expulsion of a black hole from a galaxy

But something else is still unclear in this discovery. How was the supermassive black hole ejected from its galaxy? The researchers think the ejected black hole may have escaped its galaxy following multiple collisions of supermassive black holes. The first collision likely occurred when two galaxies merged 50 million years ago.

As these black holes orbited around each other, another galaxy entered the mix, bringing with it another supermassive black hole. The interaction between the three black holes was so chaotic that it led one black hole to be flung far out into space. This means there is a good chance another black hole has entered the system and eventually replaced the original.

As the fleeing black hole moved away from its previous companions, the new pair left behind would have moved in the opposite direction. In fact, there are hints of a runaway binary black hole on the opposite side of the host galaxy from the black hole racing through space with its tail of stars.

The next step for this research will be to search for evidence of these binary black holes with NASA‘s James Webb Space Telescope and the Chandra X-ray Observatory, with the help of the study team members. Scientists are hoping for the same stroke of luck van Dokkum and his team had when they made the extraordinary observation of this massive cosmic escape.

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