In the constellation Aquila you'll find supernova remnant W50, referred to on discovery as the Manatee Nebula, a cosmic gas cloud whose remarkable feature is a galactic microquasar. A black hole and a star are orbiting each other releasing powerful jets of material. Researchers have now detected that those jets are powering a “heartbeat” of gamma-rays in the nebula some 100 light-years from the microquasar SS433.
Microquasars are made by a star feeding material to a compact object. In the case of 433, the compact object is a black hole. The jets are a consequence of this feeding process and when they interact with the surrounding interstellar medium, gamma-rays can form.
What is puzzling in the case of W50 is the sheer vastness of scale. Usually, the effect is localized, but at 100-light years away, this is not the case. Reporting in Nature Astronomy, a team has linked the gamma-ray heartbeats of the nebula to the changes in the microquasar.
The W50 supernova remnant in radio (green) against the infrared background of stars and dust (red). NRAO/AUI/NSF, K. Golap, M. Goss; NASA’s Wide Field Survey Explorer (WISE).
The star is about 30 times the mass of the Sun, and the black hole is between 10 and 20 solar masses. They orbit each other in 13 days, with the black hole siphoning matter from the star. This process has created an accretion disk of material around the black hole from which the jets are released. The researchers discovered the geometry of the disk is key.
“The accretion disk does not lie exactly in the plane of the orbit of the two objects. It precesses, or sways, like a spinning top that has been set up slanted on a table,” co-author Professor Diego Torres, from the Institute of Space Science, Barcelona, said in a statement. “As a consequence, the two jets spiral into the surrounding space, rather than just forming a straight line."
The jets take 162 days to go back to their original position. The team saw the gamma-emission from another region in the nebula with the same period. This is more than a remarkable coincidence and the team is certain that the two must be linked.
“Finding such an unambiguous connection via timing, about 100 light-years away from the microquasar, not even along the direction of the jets is as unexpected as amazing,” lead author Dr Jian Li, from the Deutsches Elektronen-Synchrotron, said. “But how the black hole can power the gas cloud's heartbeat is unclear to us.”
The team doesn’t believe that direct interaction with the jets is happening. Instead, they put forward an interesting hypothesis to explain the connection: A stream of protons might be produced around the black hole or at the edge of the jets and these are what's interacting with the rest of the nebula.
“SS 433 continues to amaze observers at all frequencies and theoreticians alike,” added Li. “[I]t is certain to provide a testbed for our ideas on cosmic-ray production and propagation near microquasars for years to come.”
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