Astronomers have revealed through a new study that they have managed to resolve 35 per cent of the high-energy X-ray background of the universe – something that they call the cosmic choir being sung in the language of X-rays.

While NASA’s Chandra mission has been instrumental in discovery of quite a few individual black holes said to be contributing to this x-ray background, NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) has upped the ante by finding large numbers of the black holes sending out the high-energy X-rays. Astronomers say that they have managed to resolve quite a lot of high-energy X-ray background – over a third of the known universe.

In a study published recently in The Astrophysical Journal, astronomers have revealed that thanks to NuSTAR they are not able to even see black holes hidden behind thick dust and gas. Over a period of time as black holes grow, the start pulling matter towards them. This intense gravity causes matter to heat up to extremely high temperatures and particles get boosted to close to the speed of light. Together, these processes make the black hole surroundings glow with X-rays. A supermassive black hole with an ample supply of fuel, or gas, will give off more high-energy X-rays.

Mapping these high-energy X-rays allow astronomers to expand their understanding of growth patterns of supermassive black holes over time. For instance, the supermassive black hole at the center of our Milky Way galaxy is dormant now, but at some point in the past, it would have siphoned gas and bulked up in size.

High-energy X-rays can reveal what lies around the most obscured supermassive black holes, which are otherwise hard to see. In the same way that medical X-rays can travel through your skin to reveal pictures of bones, NuSTAR can see through the gas and dust around black holes, to get a deeper view of what is going on inside. NuSTAR is the first telescope capable of focusing these high-energy X-rays into sharp pictures.

With NuSTAR’s more complete picture of supermassive black hole populations, astronomers can begin to puzzle together how these objects evolve and change over time. When did they start and stop growing? What is the distribution of the gas and dust that both feed and hide the black holes?

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