Scientists has found explanation to what makes black holes found in the center of galaxies to produce X-ray bursts that are known as a cosmic X-ray background and more informally X-ray songs produced by a million supermassive black holes together. It was not easy for astrophysicists to unveil source of X-ray background.

As part of a new study, scientists took help of NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) X-ray space telescope, which has collected new data about black holes, those releasing powerful X-rays. The data had played an essential role to help find source of these so called X-ray "songs." The researchers have found sources of 2% to 35% of the X-ray background.

Though it is understood that X-ray background has high pitched components, it is not understood whether it come from large number of smaller quiet sources or a few, but louder black holes. So why at very first place these super powerful X-rays are released? Gas and dust swirl around black holes, once they heat up; they travel with almost a speed of light. Also, black holes that are at the center of galaxies emit more powerful X-rays into space than those who are located somewhere where universe ends, far into the space.

“Before NuSTAR, the X-ray background in high-energies was just one blur with no resolved sources. To untangle what's going on, you have to pinpoint and count up the individual sources of the X-rays”, said Fiona Harrison, Benjamin M. Rosen Professor of Physics and Astronomy at Caltech, the principal investigator of NuSTAR, and lead author of a new study.

This new knowledge about black holes can help scientists answer more questions, such as how black holes feed and how supermassive black holes evolve within thousands of years to millions.