Supermassive black hole ejected from distant galaxy at high speed

A supermassive black hole – with a mass of perhaps a billion suns – could be ejected from its galaxy under special conditions when two black holes merge.

A supermassive black hole – with a mass of perhaps a billion suns – has been caught in the act of being ejected from its galaxy at high speed. If that galaxy were a bar, I would not like to cross paths with its bouncer.

We’ve heard for decades about supermassive black holes in the centers of galaxies. Even our own Milky Way might have its own giant black hole at its core.

The ejected object lies in a distant galaxy associated with a known X-ray source called CXO J122518.6+144545. The Hubble Space Telescope image above shows the suspected offset black hole. The white circle marks the center of the galaxy, and the red circle marks the position of the black hole leaving the galaxy at high speed.

This object was found by Marianne Heida of the University of Utrecht, working with an international team of astronomers. For her final-year project, Heida used the Chandra Source Catalog – a catalog of space objects shining in X-rays, made using the orbiting Chandra X-ray Observatory – to compare hundreds of thousands of sources of X-rays with the positions of millions of galaxies.

Normally each galaxy contains a supermassive black hole at its center. The material that falls into black holes heats up on its final journey, creating the strong X-rays often associated with black holes. Looking at one galaxy in the catalog, Heida noticed that the point of X-ray light was offset from the center and yet was so bright that it might be associated with a supermassive black hole of a billion times our sun’s mass.

Such a heavy object could be located so far from the center of a galaxy if it is being flung out of the center at high speed. The expulsion can take place under special conditions when two black holes merge. The newly formed black hole created after the merging process is then shot out of the center of the galaxy. Over the last few years various predictions have been made about the speed at which the hole would be slung away. These calculations have only recently become possible, as they require extremely powerful computers. The calculations reveal that the speed of the hole mainly depends on the direction and speed with which the two black holes rotate around their axes before merging.

Marianne Heida carried out her research at SRON Netherlands Institute for Space Research in Utrecht under the supervision of Peter Jonker. The research results have been accepted for publication in The Monthly Notices of the Royal Astronomical Society, under the title “A bright off-nuclear X-ray source: a type IIn supernova, a bright ULX or a recoiling super-massive black hole in CXO J122518.6+144545.”

Congratulations Marianne Heida on your amazing discovery! A supermassive black hole ejected from a galaxy is a wonderful addition to our conception of the universe.

Deborah Byrd