Two objects, 100 light-years apart, appear to be pulsing to the same rhythm, and it’s thought that they may be related, but it is all deeply confusing.
It all started with a black hole in a binary system with a massive star. The system is called SS 433. The black hole is gravitationally stripping material from its companion as they whirl around each other every thirteen days. That material spirals into the black hole, generating a disc that in turn drives a jet. Now, like an imperfectly spinning top, this entire spinning, orbiting mess is wobbling, with its wobble painting out a circle as it precesses. This precession causes the jets to appear as a spiral, since their origin point is going around and around, and using several years of Fermi data, a research team has figured out that precession takes 162 days. So far, so good. This is all fairly standard behavior for a microquasar.
When we widen our field of view, however, and look at the surrounding material, something weird can be seen. An otherwise average blob of gas, with the unassuming name Fermi J1913+0515, is giving off its own gamma-ray pulse every 162 days. This blob of gas isn’t aligned with where we currently see the jets pointing. The only thing tying these two systems together is their 162-day period.
According to led researcher Jian Li: 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. But how the black hole can power the gas cloud’s heartbeat is unclear to us.
According to the paper on this system, which appears in Nature Astronomy, one possibility is that the accretion disc around the black hole is also precessing, and particles from the edge of this disc are illuminating the distant gas. A possible mechanism is the release of high-energy hydrogen protons that zip through space and collide with the gas to create the periodic gamma-ray pulse. If this is the case, this is the first time this kind of system has been discovered, and a lot of theoretical work is required to try and figure out what physics best matches this bizarre system.
I’m honestly not sure how I feel about high-energy particles from a black hole’s accretion disc being able to excite gas 100 light-years away into generating gamma-rays. What I do know is that it is an area of the galaxy we probably don’t want to visit.
“Gamma-Ray Heartbeat Powered by the Microquasar SS 433,” Jian Li et al., 2020 Aug. 17, Nature Astronomy