Supermassive black holes are cosmic powerhouses, continuously emitting X-rays as they pull and feed on matter. NASA scientists have compared this cosmic X-ray background to a chorus of a million voices and, thanks to their latest X-ray observatories like Chandra and NuSTAR, the song is becoming clearer.

The groundbreaking Chandra mission has already spotted many of the "choir singers", but NuSTAR's job is to find the most energetic supermassive black holes – the sopranos, the high-pitched singers of this universal choir.

“We've gone from resolving just two percent of the high-energy X-ray background to 35 percent," said Fiona Harrison, the principal investigator of NuSTAR at Caltech in Pasadena, in a statement. "We can see the most obscured black holes, hidden in thick gas and dust."

These findings are described in a new study that will be published in The Astrophysical Journal. Using this new data, the team hopes to understand how black hole feeding mechanisms change over time, which will also help researchers understand how they grow and how quickly.

The research will also have an impact on refining the current picture of galaxy evolution. There are profound links between supermassive black holes and their host galaxies, both in term of mass and dynamics, and NuSTAR is the first one capable of viewing the most powerful supermassive black holes in detail.

"We knew this cosmic choir had a strong high-pitched component, but we still don't know if it comes from a lot of smaller, quiet singers, or a few with loud voices," added co-author Daniel Stern, the project scientist for NuSTAR at NASA’s Jet Propulsion Laboratory. "Now, thanks to NuSTAR, we're gaining a better understanding of the black holes and starting to address these questions."

NuSTAR still has a long way to go, and its sharp eye will hopefully continue to solve the mystery of supermassive black holes.