NASA's black-hole-hunter spacecraft has discover 10 of them, and they are of the  supermassive kind.

The Nuclear Spectroscopic Telescope Array (NuSTAR) is as long as a school bus, and is the first of its kind to have the ability to focus "the highest-energy X-ray light into detailed pictures," a NASA press release reported.

"We found the black holes serendipitously," lead author David Alexander, a NuSTAR team member of the Department of Physics at Durham University, said. "We were looking at known targets and spotted the black holes in the background of the images."

The mission will last for two more years, and researchers expect to find hundreds more supermassive black holes over that period.

After NuSTAR made its 10 discoveries, researchers went back and looked at data from lower-energy X-ray light telescopes. They were able to detect the presence of the black holes in the lower quality images, but would have most likely missed them without NuSTAR. Researchers hope they will one day be able to count the number of black holes in the universe.

"We are getting closer to solving a mystery that began in 1962," Alexander said."Back then, astronomers had noted a diffuse X-ray glow in the background of our sky but were unsure of its origin. Now, we know that distant supermassive black holes are sources of this light, but we need NuSTAR to help further detect and understand the black hole populations." 

The mission aims to solidly identify what is causing the glow (called the cosmic X-ray background) detected by NuSTAR.

"The highest-energy X-rays can pass right through even significant amounts of dust and gas surrounding the active supermassive black holes," Fiona Harrison, a study co-author and the mission's principal investigator at the California Institute of Technology, Pasadena, said.

NASA's Wide-field Infrared Survey Explorer (WISE) has been helping out by weighing the mass of galaxies around the black holes.

"Our early results show that the more distant supermassive black holes are encased in bigger galaxies," Daniel Stern, a co-author of the study and the project scientist for NuSTAR at NASA's Jet Propulsion Laboratory, said. "This is to be expected. Back when the universe was younger, there was a lot more action with bigger galaxies colliding, merging and growing."