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About 15,000 light-years away, an active black hole appears to periodically illuminate an otherwise unremarkable gas cloud with gamma rays. But there is a catch. The gas cloud is about 100 light years from the black hole – and how the cloud pulsates in time with it is a mystery.
It is unlikely, according to astrophysicists, that the pulses are directly generated by the jets of plasma emitted by active black holes. But it’s possible that the black hole is somehow projecting cosmic rays in a way that illuminates the gas cloud.
“This result calls into question obvious interpretations and is unexpected compared to previously published theoretical models,” said astrophysicist Jian Li of Deutsches Elektronen-Synchrotron in Germany.
“This gives us a chance to uncover the particle transport of SS 433 and probe the structure of the magnetic field in its vicinity.”
SS 433 is the black hole system, of a type known as a microquasar. It consists, of course, of the black hole – a relatively irritable type, weighing 10 to 20 times the mass of the Sun. Its binary companion is a main sequence supergiant, about 30 times the mass of the Sun.
The two are stuck in a very close orbit, just a hair’s breadth over 13 days, so the black hole siphons a constant stream of material from its stellar companion, wrapping around it like water around a drain. . In doing so, the material shines, just like a mini version of a quasar.
But not all the material is absorbed. Some of it is vented from the inner edge of the accretion disk around the outside of the black hole – we’re not quite sure how, but scientists believe it’s along the magnetic field lines.
This material is then radiated far – presumably – from the poles of the black hole in jets of plasma that can approach significant percentages of the speed of light.
In addition, the black hole of SS 433 wobbles, like a top, on its axis of rotation. This oscillation is called rotational precession, and it means that the jets, rather than firing in a straight line, soar through space, as shown in the video below from another previous microquasar, the V404 Cygni.
By observing SS 433 for a decade, Li and his team were able to determine that the black hole precession had a periodicity of just over 162 days, with the jet losing its spiral shape and relaxing into a cone after a few cycles. And the gas cloud vibrates with gamma radiation at the same time scales.
It may seem like an open and closed case, but there is a big problem. The cloud is not actually in the extrapolated jet cone.
“Finding such a clear connection by synchronization, about 100 light years from the micro quasar, not even in the direction of the jets, is as unexpected as [it is] amazing, ”Li said. But how the black hole can fuel the heartbeat of the gas cloud is not clear to us. “
It may not be clear, but that doesn’t mean there aren’t potential explanations. Cosmic rays – high-energy protons that travel almost at the speed of light – may be produced by the black hole, either at the ends of the jets or from its equator.
At the ends of the jets, or near the black hole, the subatomic particles of cosmic rays could be ejected towards the cloud. When they hit it, the impact could then produce gamma rays, as described in a theoretical paper from 2005.
Or it is possible that the cosmic rays are coming from the edge of the accretion disk.
“On an energetic level, the output of the disc could be as powerful as that of the jets and it is believed that it precedes in solidarity with the rest of the system,” explained astrophysicist Diego Torres from the Institute of Space Sciences in Spain. .
These cosmic rays should be emitted at a speed sufficient to produce the observed gamma ray emission. This, according to the researchers, is difficult to reconcile with our current understanding of the source environment.
So there’s a lot more work to be done to understand the system – and how it lights up a cloud of gas 100 light years away.
“The SS 433 continues to amaze observers at all frequencies and theorists,” the researchers wrote, “and is certain to provide a testing ground for our ideas on the production and propagation of cosmic rays near microquasars. for the coming years.”
The research was published in Nature astronomy.
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