For the first time, researchers have discovered a pair of supermassive black holes orbiting one another in an ordinary galaxy. An international research team was able to discover them after the black holes ripped apart a star exactly when ESA's space observatory XMM-Newton was looking into their direction.

Previously, XMM-Newton spotted a tidal disruption event in galaxy SDSS J120136.02+300305.5 on June 10, 2010. It was approximately two billion light years away.

Usually, XMM-Newton looks at a fixed point for some time before slewing to the next fixed point. Scientists keep it on as it turns to see if anything unusual is happening up there. And this is what exactly happened, as the observatory caught X-rays from a faraway galaxy. The findings of the study are expected to be published in the May 10 issue of the Astrophysical Journal.

It is very rare to spot two supermassive black holes as most massive galaxies in the universe are known to have one supermassive black hole at the center. Scientists said that the unusual find means that the galaxy has merged with another.

All the double black hole galaxies discovered by scientists are active as of now, which means that they are constantly ripping gas clouds apart to eventually crush them out of existence. The destruction process heats the gas so much that it shines at many wavelengths, including X-rays. As a result, the galaxy gets an unusually bright center and makes it active.

However, the galaxy was not active in this case, as researchers did not notice any continuous x-ray stream coming out of it. Instead, X-rays were seen dimming and brightening. This led the researchers jump at the assumption of two black holes not one.

"This is exactly what you would expect from a pair of supermassive black holes orbiting one another", said lead author Fukun Liu from Peking University in China.