New observations of the galaxy Messier 101 have yielded the discovery of an unusual black hole that can sustain a hugely voracious appetite while consuming material in an efficient and tidy manner – something previously thought impossible.
Messier 101 (M101), also known as the Pinwheel Galaxy or NGC 5457, is a spiral galaxy located in the constellation Ursa Major about 22 million light-years away from Earth.
In 2004, Chandra and XMM-Newton space observatories detected an ultraluminous X-ray source (ULX) in this galaxy.
X-ray sources give off high- and low-energy X-rays, which astronomers call hard and soft X-rays, respectively. In what might seem like a contradiction, larger black holes tend to produce more soft X-rays, while smaller black holes tend to produce relatively more hard X-rays.
The X-ray source in Messier 101, labeled ULX-1, is dominated by soft X-rays, so scientists expected to find a larger black hole as its energy source. In a surprising twist, however, the new observations indicate that ULX-1’s black hole is on the small side, and they don’t understand why.
The new data suggest that this black hole is unexpectedly lightweight (20-30 times the mass of our Sun), and, despite the generous amount of dust and gas being fed to it by a massive stellar companion, it swallows this material in a surprisingly orderly fashion.
“It has elegant manners. Such lightweights must devour matter at close to their theoretical limits of consumption to sustain the kind of energy output observed,” said Dr Stephen Justham from the National Astronomical Observatories of China, a co-author of the article published in Nature.