Microquasar detected emitting high energy radiation from its outer reaches, not its core
Results from 1000 days of data have caught astrophysicists by surprise. Ben Lewis reports.
For the first time, scientists have detected a stream of gamma-radiation coming from the outermost regions of a microquasar – a compact stellar object that mimics the behaviour of a quasar.
The research, led by Jordan Goodman from the University of Maryland, US, is published in the journal Nature.
Microquasars are black holes that consume matter from nearby companion stars. Their interaction blasts out two powerful jets of very high energy particles and radiation. The microquasar that has intrigued astronomers in this study, named SS 433, is about 15,000 light-years from Earth.
Other microquasars have been observed with emission jets orientated towards Earth, like a flashlight being shone in its direction. SS 433, on the other hand, has its jets aimed away from Earth, suggesting an alternative source for the gamma rays detected.
Examining more than 1000 days of data captured at the High-Altitude Water Cherenkov Gamma-Ray Observatory, (HAWC) observatory, in Mexico, the team found that gamma rays were coming from the ends of the microquasar’s jets, not from the central region where the jets themselves are produced.
This, they suggest, could mean extremely high-energy electrons are colliding with the low-energy microwave background radiation that permeates space, resulting in gamma rays scattered in all directions, including towards Earth.
The formation of gamma rays in this way has never been seen before.
The discovery also raises questions about how the electrons are accelerated to the high energies required. The researchers write that the evidence suggests they are accelerated to the required levels as they approach the ends of the jets. However, the current models do not adequately explain how this could occur.
Future studies could examine the possibility of very concentrated magnetic fields, or standing shocks along the jets that could create this force, the researchers suggest.