Washington, Sep 1 - Astronomers have discovered a pair of supermassive black holes in a spiral galaxy similar to the Milky Way, NASA said Wednesday.
Approximately 160 million light years from Earth, the pair is the nearest known such phenomenon, said scientists at NASA's Chandra X-ray Observatory.
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses.
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.
Both the black holes are heavily obscured by dust and gas, which makes them difficult to observe in optical light.
Sine X-rays are more energetic, they can penetrate this obscuring material, Xinhua reported quoting the experts.
They said that Chandra's X-ray spectra show clear signatures of a pair of supermassive black holes.
"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 Centre for Astrophysics, who led the study published in the online edition of the journal Nature Wednesday.
"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," he said.
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.
When two equal-sized spiral galaxies merge, astronomers think it should result in the formation of a black hole pair and a galaxy with a disrupted appearance and intense star formation.
A well-known example is the pair of supermassive black holes in NGC 6240, which is located about 330 million light years from Earth.
However, NGC 3393 is a well-organized spiral galaxy, and its central bulge is dominated by old stars. These are unusual properties for a galaxy containing a pair of black holes, said the experts. (IANS)