Black hole spotted racing across galaxy

Astronomers have been following what appears to be a speedy black hole racing across its home galaxy.

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The main image shows an artist’s illustration of a black hole being recoiled across space. Left inset is Hubble optical data showing two bright points at the centre of a galaxy. This, according to a new study, could suggest the recoiling of a supermassive black hole following the merger of two smaller black holes.
Credit: Illustration: CXC/M. Weiss; X-ray: NASA/CXC/NRAO/D.-C. Kim; Optical: NASA/STScI

Astronomers believe they may have discovered a black hole being flung across a galaxy 3.9 billion lightyears from Earth.

Most galaxies contain a supermassive black hole at their centre, and it is unusual to find them on the move, but one specimen that is 160 million times the mass of our Sun seems to be travelling across its home galaxy.

It is thought the black hole may have been formed via the merger of two smaller black holes, and that this action created a recoil force that has pushed it away from the galactic centre.

The merging of the black holes could have generated gravitational waves that were more strong in one direction than others. The black hole would then be kicked in the opposite direction of the stronger waves.

 


Read more about wandering black holes from BBC Sky at Night Magazine:


 

Because the strength of the kick is dependent upon the rate and direction of the spin of the two black holes before they merged, astronomers can study the speed of the recoiled black hole to learn more about how the two smaller black holes were behaving before they clashed.

The speedy black hole was discovered by a team of astronomers looking through X-ray and optical data for thousands of galaxies; specifically those with bright X-ray centres indicating the presence of a growing black hole.

Then, optical light observations using the Hubble Space Telescope revealed whether any of these galaxies showed two peaks of light near their centre, as this would indicate a pair of supermassive black holes or else the recoil of a supermassive black hole away from the centre of the galaxy.

Hubble data of one galaxy showed two bright points: one near the centre and one about 3,000 lightyears away. The latter source displayed properties of a growing supermassive black hole.

The astronomers determined that the growing black hole near the centre has a velocity different from the rest of the galaxy, indicating a black hole on the move.

They also noticed that the galaxy contains evidence of disturbances in its outer regions, suggesting a violent black hole merger occurred in its recent past.


Carousel image: artist's impression of two supermassive black holes merging
Credit: NASA
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