As well as consuming enormous amounts of matter, black holes also return a lot of energy to the Universe. When mass is attracted to black holes, this in turn causes the release of powerful X-ray radiation and strong jets of particles.
The variations between how this happens in different black holes have puzzled astronomers for a long time, but a study from the SRON Netherlands Institute for Space Research may have alighted on the reason for this divergence. The team believe that black holes may be likened to a large and efficient engine which can effectively change gear.
Set to appear in two papers in the Monthly Notices of the Royal Astronomical Society
, the research builds upon the discovery in 2003 that the jet outflow and the X-ray emissions from black holes are interconnected. It was assumed at first that this connection worked in the same way for all feeding black holes, but it soon transpired that this was not the case as ‘oddballs’ were found.
While the connection remained in these apparently anomalous examples, the proportions were different. Attempts to explain this with theories about two separate types of black hole as the number of supposed 'oddballs' grew were unsuccessful, but Michael Coriat – now at the University of Southampton – and his team recently observed one black hole which seemed to switch between the two different types.
Peter Jonker and PhD student Eva Ratti from SRON Netherlands Institute of Space Research have added weight to the hypothesis inferred from those observations that black holes, rather than occurring as two kinds of ‘engine’, are akin to one kind of engine with two distinct ‘gears’.
Using X-ray data from the Chandra X-ray Observatory and radio observations from the Expanded Very Large Array in New Mexico, the scientists charted the activity of two black holes up until the end of their so-called ‘feeding frenzies’.
"We found that these two black holes could also 'change gear', demonstrating that this is not an exceptional property of one peculiar black hole," remarked Ratti. "Our work suggests that changing gear might be common among black holes. We also found that the switch between gears happens at a similar X-ray luminosity for all the three black holes."
The work may have an important bearing on future theoretical models of the way black holes function, as well as contributing to our understanding of how they influence their astronomical neighbours.