An international team of astronomers has conducted some detailed observations of two different black holes and was able to learn a little bit more about their jets. The researchers measured how quickly they turn on and how bright they shine, which provides some insight into their complex physics.
As reported in Nature Astronomy, the team was able to determine the “acceleration zone” of the black holes, i.e. the distance particles need to speed up around the cosmic object before they start emitting powerfully bright light. Those accelerated particles end up forming the jets but the cause of their acceleration is not clear.
To better understand it, the team looked at two “X-ray binaries”, V404 Cygni and GX 339-4. Both systems are made of a black hole and a star, and the black hole feeds on the material from the star. The material surrounds the black hole forming an accretion disk. Some of it will shoot outwards to form the jet.
“One of the best ways of observing a black hole is in a binary system, where the black hole is in orbit with a star and pulling gas from it. Some of this gas doesn't fall into the event horizon of the black hole, but is instead ejected in the form of a jet emanating from close to the black hole,” co-author Professor Vik Dhillon, from the University of Sheffield, said in a statement.
The current scenario suggests that X-rays are produced by material very close to the black hole. This material is accelerated by strong magnetic fields and encounters other particles. The collision generates optical light. By using the time delay between the optical and X-ray signals, the team was able to establish that the acceleration zone is about 30,000 kilometers (19,000 miles).
These observations are similar to the effects observed in the supermassive black holes at the center of galaxies. For example, in the galaxy BL Lacertae, the time delay was millions of times greater.
"We are excited because it looks as though we have found a characteristic yardstick related to the inner workings of jets, not only in stellar-mass black holes like V404 Cygni, but also in monster supermassive ones," lead author Poshak Gandhi, from the University of Southampton, said in a statement.
The team is now planning observations of more X-ray binaries as well as producing a theory to explain the jet formation for black holes of all sizes.