This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:. Our home planet is bombarded with particles from outer space all the time. And while we are mostly familiar with the rocky meteorites originating from within our solar system that create fascinating shooting stars in the night sky, it's the smallest particles that help scientists to understand the nature of the universe.
Subatomic particles such as electrons or protons arriving from interstellar space and beyond are one of the fastest particles known in the universe and known as cosmic rays. The origins and the acceleration mechanisms of the most energetic of these cosmic particles remains one of the biggest mysteries in astrophysics. Fast-moving matter outflows or "jets" launched from black holes would be an ideal site for particle acceleration, but the details on how and under which conditions acceleration processes can occur are unclear.
The most powerful jets inside our galaxy occur in microquasars: systems composed by a stellar-mass black hole and a "normal" star. The pair orbit each other, and, once they are close enough, the black hole starts to slowly swallow its companion. As a consequence of this, jets are launched from the region close to the black hole. In the past couple of years there has been growing evidence that microquasar jets are efficient particle accelerators.
It is, however, unclear how much they contribute, as a group, to the total amount of cosmic rays in the galaxy. The answer to this question requires understanding if all microquasars are able to accelerate particles or only a lucky few. Microquasars are usually classified depending on the mass of the star in the system into either "low-mass" or "high-mass" systems, with lower-mass systems being much more abundant.
However, up until now, evidence of particle acceleration was only found for the high-mass systems. For example, the microquasar SS , which was recently revealed to be one of the most powerful particle accelerators in the galaxy, contains a star with a mass approximately 10 times that of the sun.
