Ultraluminous X-ray Source (ULX) that astronomers had thought was a
black hole is really the brightest pulsar ever recorded. ULXs are
objects that produce more X-rays than most “normal” X-ray binary
systems, in which a star is orbiting a neutron star or a stellar-mass
black hole. Black holes in these X-ray binary systems generally weigh
about five to thirty times the mass of the sun.
Astronomers used NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array)
and Chandra X-ray Observatory to study two ULXs in the center of M82, a
galaxy located just over 11 million light years from Earth. This
composite image shows X-rays from NuSTAR (purple) and Chandra (blue)
that have been combined with optical data from the NRAO 2.1-meter
telescope (gold). The extended X-ray emission is unrelated to the two
ULXs.
Until now, astronomers have thought that matter falling onto black holes
powered the bright X-ray emission in all ULXs. Most of the black holes
in ULXs are thought to weigh at least 10 to 50 times the mass of the
sun, but some of the brightest ULXs are thought to weigh 100 times the
sun’s mass, or more.
