Black holes can be really, really big – supermassive, if you will – and they can also be quite small, relatively speaking. But do any exist between these two extremes? Finding evidence for such mid-sized black holes has been difficult until now.
But a new study published in Astrophysical Journal Letters has found evidence for such an intermediate-mass black hole, roughly 5,000 times the mass of the Sun. For comparison, supermassive black holes at the center of galaxies measure up to several billion times the Sun’s mass, while stellar mass black holes are just a few dozen times the mass of the Sun.
This latest discovery, by a team from the University of Maryland (UMD), adds to about a half-dozen other intermediate black hole candidates that had been found before. It has been named NGC1313X-1, found in the galaxy NGC1313 about 14 million light-years from Earth. It was found using data from ESA’s XMM-Newton satellite, which was able to spot the ultraluminous X-rays coming from the black hole.
"This result provides support to the idea that black holes exist on all size scales," said lead author Dheeraj Pasham, a postdoctoral associate at the Joint Space-Science Institute, a research partnership between UMD's Departments of Astronomy and Physics and NASA Goddard.
Some of this same team had found a similar black hole last year, weighing 400 times the mass of the Sun, using NASA’s Rossi X-ray Timing Explorer (RXTE) satellite. But Pasham said that subsequent findings like this are needed to confirm the new class of black hole. "When you describe something for the first time, there is always some doubt," he said. "Identifying a second candidate with a different instrument puts weight behind both findings and gives us confidence in our technique."
This black hole was also found to have a pair of repeating flares, one flashing 27.6 times per minute and the other 17.4 times per minute, a ratio of exactly 3:2. While the cause of these flashes of light is not known, the 3:2 ratio is thought to be common to similarly sized or smaller black holes.
In 2016, NASA is planning to launch a new X-ray telescope called the Neutron Star Interior Composition Explorer (NICER), which the team hope to use to study their new intermediate black hole candidate – and others – further.