London, Sept 01 : The first pair of super massive black holes in a spiral galaxy similar to the Milky Way has been discovered by astronomers using NASA''s Chandra X-ray Observatory.

Approximately 160 million light-years from Earth, the pair is the nearest known such phenomenon.

The black holes are located near the centre of the spiral galaxy NGC 3393. Separated by only 490 light-years, the black holes are likely the remnant of a merger of two galaxies of unequal mass a billion or more years ago.

"If this galaxy weren't so close, we'd have no chance of separating the two black holes the way we have," said Pepi Fabbiano of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who led the study.

"Since this galaxy was right under our noses by cosmic standards, it makes us wonder how many of these black hole pairs we've been missing," added Fabbiano.

Previous observations in X-rays and at other wavelengths indicated that a single supermassive black hole existed in the centre of NGC 3393.

However, a long look by Chandra allowed the researchers to detect and separate the dual black holes. Both black holes are actively growing and emitting X-rays as gas falls towards them and becomes hotter.

Both of the supermassive black holes are heavily obscured by dust and gas, which makes them difficult to observe in optical light. Because X-rays are more energetic, they can penetrate this obscuring material.

Chandra''s X-ray spectra showed clear signatures of a pair of supermassive black holes.

The finding has been detailed in online issue of the journal Nature. (ANI)