Astronomers have found a pulsating, dead star beaming with the energy of about 10 million suns. This is the brightest pulsar - a dense stellar remnant left over from a supernova explosion - ever recorded. The discovery was made with NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR. "You might think of this pulsar as the 'Mighty Mouse' of stellar remnants," said Fiona Harrison, the NuSTAR principal investigator at the California Institute of Technology in Pasadena. "It has all the power of a black hole, but with much less mass." The discovery appears in a new report in the Thursday, Oct. 9, issue of the journal Nature. The surprising find is helping astronomers better understand mysterious sources of blinding X-rays, called ultraluminous X-ray sources (ULXs). Until now, all ULXs were thought to be black holes. The new data from NuSTAR show at least one ULX, about 12 million light-years away in the galaxy Messier 82 (M82), is actually a pulsar. "The pulsar appears to be eating the equivalent of a black hole diet," said Harrison. "This result will help us understand how black holes gorge and grow so quickly, which is an important event in the formation of galaxies and structures in the universe." ULXs are generally thought to be black holes feeding off companion stars -- a process called accretion. They also are suspected to be the long-sought-after "medium-size" black holes - missing links between smaller, stellar-size black holes and the gargantuan ones that dominate the hearts of most galaxies. But research into the true nature of ULXs continues toward more definitive answers. NuSTAR did not initially set out to study the two ULXs in M82. Astronomers had been observing a recent supernova in the galaxy when they serendipitously noticed pulses of bright X-rays coming from the ULX known as M82 X-2. Black holes do not pulse, but pulsars do. via JPL | News.