As supermassive black holes attract matter (gas, dust, stars etc.) from the center of their host galaxies, they create a mashed-up, hot accretion disk before the mass is accelerated to relativistic speeds and falls into the black hole, bulking it up. These active black holes cause their accretion disks to generate huge quantities of X-rays and the energy of this radiation gives astronomers clues as to black holes' feeding habits and therefore their evolution.
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So by tracking down the highest-energy X-ray sources, NuSTAR is gradually revealing the nature of some of the most energetic events in the cosmos.
"Before NuSTAR, the X-ray background in high-energies was just one blur with no resolved sources," said Harrison. "To untangle what's going on, you have to pinpoint and count up the individual sources of the X-rays."
"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," said Daniel Stern, project scientist for NuSTAR at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Now, thanks to NuSTAR, we're gaining a better understanding of the black holes and starting to address these questions."
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Interestingly, these highest-energy X-ray sources are often hidden deep inside dust-filled galactic cores and have therefore been invisible. But NuSTAR is able to see through this gas and dust to precisely resolve some of the most active (and therefore "loudest") supermassive black hole emissions that would have otherwise remained buried.
This research will be published in an upcoming issue of The Astrophysical Journal.