An international team of astronomers has discovered a most unusual system — one in which a gas cloud is sending out a ‘heartbeat’ of gamma rays in time with the pulses of a nearby black hole, despite being located 100 light-years away. The system demonstrating this highly unexpected and mysterious behavior is called SS 433, located 15,000 light-years away in the constellation of Aquila.
The black hole in question is part of a system that includes a giant star which is about 30 times the mass of our sun, and the two objects are close together, orbiting each other every 13 days. The black hole is gradually sucking away matter such as gas from the star and devouring it.
The black hole gives off pulses due to the way matter falls into it. “This material accumulates in an accretion disc before falling into the black hole, like water in the whirl above the drain of a bath tub,” lead author Jian Li of the German research center Deutsches Elektronen-Synchrotron explained in a statement. “However, a part of that matter does not fall down the drain but shoots out at high speed in two narrow jets in opposite directions above and below the rotating accretion disk.”
These jets produce gamma rays and sway back and forth like a spinning top, creating a spiral with a period of 162 days. This behavior is familiar to astronomers as it is similar to a smaller-scale version of a type of black hole called a quasar. Therefore it’s referred to as a microquasar.
So far, so typical. But things got really weird when the researchers looked at an apparently unremarkable cosmic dust cloud located relatively far away from the black hole. This gas cloud, called Fermi J1913+0515, is located 100 light-years away and yet is giving out a gamma ray signal with exactly the same period of 162 days. Scientists are baffled as to how this could be the case as the cloud seems to be too far away from the microquasar to be directly illuminated by it.
“Finding such an unambiguous connection via timing, about 100 light years away from the micro quasar, not even along the direction of the jets is as unexpected as amazing,” Li said. “But how the black hole can power the gas cloud’s heartbeat is unclear to us.”
The researchers theorize that there could be protons created at the ends of the jets interacting with the cloud and producing gamma rays, or that the outflow from the jets could be hitting the cloud and causing the pulses. But they say they’ll need to collect more data and develop new theories about how black holes interact with their surroundings to understand this unique system.
“SS 433 continues to amaze observers at all frequencies and theoreticians alike,” Li said. “And it is certain to provide a testbed for our ideas on cosmic-ray production and propagation near micro quasars for years to come.”
The findings are published in the journal Nature Astronomy.
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