Recently, we discussed the discovery of a black hole in a neighboring galaxy. It appears to be swallowing matter at a rate that's close to the theoretical limit on this process. This discovery raises the hope that we'll be able to get a clear view of the environment around the black hole, where the inflow of matter leads to the formation of particle jets that expel some of the matter at relativistic speeds. This process is also thought to power quasars, where the jets of supermassive black holes generates some of the brightest objects in the Universe.
But there's a small caveat that should temper astronomers' enthusiasm: we don't know for a fact the same process that powers jets from small black holes can scale up to objects that may weigh billions of times the mass of the Sun. Conveniently, in the same week this discovery was announced, another team of astronomers has provided evidence that all of these jets have similar properties.
Although black holes are happy to swallow most of the matter that comes their way, a bit of it escapes—if by "escapes" we mean "gets shot away from the black hole at nearly the speed of light." These jets of particles are so energetic that, in at least some cases, they're entirely thrown out of the galaxy where the black hole resides. Various models indicate the black hole's intense magnetic field lines power the jets by latching on to charged particles in the matter that is falling in towards the event horizon.
We've got some great models of how this can work and how the environment narrows and focuses the jets, sending them in a beam lined up with the black hole's north and south pole. But we're only just starting to resolve some of the features near the black holes at the center of quasars. Given that most quasars are quite distant and the core of galaxies are crowded places, there are likely to be limits to how well we can ever resolve the details of the environment that forms the jets.
That explains the appeal of objects like gamma ray bursts (which result from a black hole's formation) and microquasars (stellar-mass black holes actively swallowing matter). These have been found much closer to Earth (including in our own galaxy) and don't necessarily reside in the galactic center, which means we should be able to get a relatively unobstructed view of one. And, with a bit of luck, we could potentially get a clearer perspective on the jets' formation.
But that raises the question of whether what we learn from these smaller bodies is actually relevant to black holes. Remember, these are so big that, if you dropped one in place of the Sun, its edges would extend out past the most distant planets. Earlier studies had suggested that microquasars and the full-sized versions operate through a similar process. The new study now extends this to gamma-ray bursts.
The authors searched for any reports of observations of the jets of black holes, ranging in size from the gamma-ray bursts that accompany the formation of black holes up to the blazars that are generated by supermassive black holes in galactic cores. These objects create gamma ray emissions as charged particles are whipped around at the base of the jets as they form. They also used radio observations to track the total energy in the jets.
When the two values were plotted against each other, the resulting points all fell along a single line. This suggests there's a simple, linear relationship between the two: the more energy in the jets, the stronger the gamma rays they can produce. So perhaps, there is indeed a single mechanism for accelerating the particles into a jet, one that works across all masses of black holes. The apparent mass independence should help constrain the models we make of jet formation and will mean that any information we get from one object will tell us about the remaining ones.
Science, 2012. DOI: 10.1126/science.1227416 (About DOIs).
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