Scientists observe black hole with mass of 20 million suns escaping galaxy

A supermassive black hole appears to have been ejected into interstellar space at 4,500 times the speed of sound.
Chris Young
An illustration of a blackhole
An illustration of a blackhole


Astronomers spotted a runaway supermassive black hole that appears to have been powerfully ejected from its home galaxy.

And it's taking part of that galaxy with it.

The new observations, detailed in a new paper in preprint server arXiv, show how the colossal giant is dragging a group of stars in its wake. It is the first observational evidence that black holes can be ejected from their home galaxies into interstellar space.

A runaway supermassive black hole

The scientists behind the discovery discovered the runaway black hole in Hubble Space Telescope observations of the dwarf galaxy RCP 28, located roughly 7.5 billion light-years from Earth. 

They detected a bright streak of light in those images, prompting them to conduct follow-up observations of the region using the Keck telescope in Hawaii.

With the Keck telescope data, they determined that the streak measures more than 200,000 light-years across — meaning it's rough twice the width of the Milky Way — and it's likely made of compressed star-forming gas. The researchers tracked that streak of gas back to the galaxy's center, where a supermassive black hole would typically reside.

The researchers determined that this jumping black hole measures an estimated 20 million times the sun's mass and is speeding away from its galaxy at a massive 3.5 million mph (5.6 million km/h), or roughly 4,500 times the speed of sound.

"Clear evidence" of supermassive black hole escaping galaxy

The researchers conducted extensive analysis of their data to determine the streak of gas wasn't some other phenomenon, such as high-powered jets that are known to shoot away from supermassive black holes.

"We found a thin line in a Hubble image that is pointing to the center of a galaxy," lead study author Pieter van Dokkum, a professor of physics and astronomy at Yale University, told Live Science in an interview. "Using the Keck telescope in Hawaii, we found that the line and the galaxy are connected. From a detailed analysis of the feature, we inferred that we are seeing a massive black hole ejected from the galaxy, leaving a trail of gas and newly formed stars in its wake." 

The researchers believe their observations provide the first observational evidence of a supermassive black hole being ejected into interstellar space. "If confirmed, it would be the first time that we have clear evidence that supermassive black holes can escape from galaxies," van Dokkum said.

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