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Astronomers have detected gamma rays from the outermost regions of an unusual star system in our Milky Way. The source is a microquasar – a black hole that engulfs objects from a nearby star and projects two powerful jets of material. The observations suggest that acceleration of electrons and collisions at ends of jets of microquasar produced powerful gamma rays.
The SS 433 is a microquasar located in the constellation of Aquila, about 15 000 light-years from Earth. Image credit: L. Calçada / ESO.
Quasars are massive black holes that suck material from the centers of galaxies, rather than feeding on a single star. They actively emit visible radiation throughout the universe.
But most are so far away that the majority of the detected quasars must have their jets directed towards the Earth, which makes them easier to spot, as if you are looking directly into a flashlight.
On the other hand, the jets of a small scale version of the quasar called SS 433 are far from the Earth, making them more difficult to observe.
"Our results improve the understanding of particle acceleration in microquasar jets, which also illuminates jet physics in much larger and more powerful extragalactic jets in quasars," said Dr. Hao Zhou. co-lead author, researcher in the Physics and Theoretical Divisions at the Los Alamos National Laboratory.
Dr. Zhou and his colleagues collected data from the high-altitude gamma-ray observatory (HAWC) in Cherenkov water, a detector located at the top of a mountain in Mexico that observes the emission of gamma rays by the remains supernova, dense rotating stars called pulsars and quasars.
They examined HAWC data collected for more than 1,017 days of observation SS 433 and found that gamma rays originated from the ends of the jets of the microquasar, rather than the central part of the star system.
On the basis of their analysis, astronomers have concluded that jet electrons reach energies about 1,000 times higher than those obtainable with Earth-bound particle accelerators, such as the Large Hadron Collider.
The jet electrons collide with the low-energy microwave background radiation that enters the space, causing gamma-ray emission.
It is a recently observed mechanism to extract high energy gamma rays from this type of system. It differs from what scientists have observed when the jets are directed towards the Earth.
"What is amazing in this discovery is that all current theories on particle acceleration have difficulty explaining observations," said co-author Dr. Hui Li, theorist at Theoretical Division of Los Alamos National Laboratory.
"This certainly calls for new ideas on particle acceleration in microquasars and black hole systems in general."
The results were published in the October 4, 2018 issue Nature.
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A.U. Abeysekara et al. 2018. Acceleration of very high energy particles fed by the jets of the microquasar SS 433. Nature 562: 82-85; doi: 10.1038 / s41586-018-0565-5
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