Strong winds around black holes in binary systems

Artist's concept of winds around a black hole stealing gas from a companion (Image courtesy NASA/Swift/A. Simonnet, Sonoma State University)
Artist’s concept of winds around a black hole stealing gas from a companion (Image courtesy NASA/Swift/A. Simonnet, Sonoma State University)

An article published in the journal “Nature” describes the study of 12 binary systems with X-ray emissions and the presence of a black hole. A team of researchers found evidence of the continuous presence of strong winds that surround the black holes studied throughout their outbursts, which consist in very intense emissions. This research offers new information on the way in which masses move towards black holes and on black holes’ influence on the environment around them.

Researchers have long known that stellar remnants, not just black holes but also neutron stars and white dwarfs, can be surrounded by streams of materials that may have been torn from a companion star. However, the mechanisms that regulate these processes are known in part but a lot of data were collected over the last 20 years by the RXTE (Rossi X-ray Timing Explorer), Swift, Chandra and XMM-Newton space telescopes. Now the data about 21 outbursts in 12 binary systems have been put together and studied.

An interesting conclusion of the authors of this new research was that magnetic fields are a very important factor in the phenomena related to the winds that surround black holes. There are no precise explanations yet but the researchers identified the importance of distance of the materials from the black hole to understand what happens to them.

Everything that falls within a radius that for black holes generated by stellar remnants ranges from 3 to 150 kilometers is slowly swallowed, even light. Instead, what’s a bit beyond a kind of safety distance is probably ejected from that area and projected far away.

The winds that are produced can sweep away a very large part of the materials in the area around that type of black hole. The researchers created models based on the data examined, which are still imprecise, and according to one of the possibilities they calculated those winds can sweep away even 80% of the materials present, subtracting them from the black hole.

The conclusion regarding the importance of magnetic fields in these mechanisms may seem strange considering that an article published in the journal “Science” in December 2017 reported that a precise measurement of the magnetic field of the corona of the black hole V404 Cygni was about 400 times lower than the previous estimates. This shows how much there’s still to be understood about these phenomena.

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