Scientists have detected an intense wind from one of the closest known black holes to the Earth, by using the biggest optical-infrared telescope in the world.

During observations of V404 Cygni, which went into a bright and violent outburst in June last year after more than 25 years of quiescence, the team began taking optical measurements of the black hole's accretion disc using the 10.4m Gran Telescopio CANARIAS (GTC), situated at the Roque de los Muchachos Observatory in the Canary Islands.

The results show the presence of a wind of neutral material (unionised hydrogen and helium), which is formed in the outer layers of the accretion disc, regulating the accretion of material by the black hole.

This wind, detected for the first time in a system of this type, has a very high velocity (3,000 kilometres per second) so that it can escape from the gravitational field around the black hole.

"Its presence allows us to explain why the outburst, in spite of being bright and very violent, with continuous changes in luminosity and ejections of mass in the form of jets, was also very brief, lasting only two weeks," said Professor Phil Charles from Physics and Astronomy Department at the University of Southampton in the UK.

At the end of this outburst, GTC observations showed the presence of a nebula formed from material expelled by wind.

This phenomenon, which has been observed for the first time in a black hole, also allows scientists to estimate the quantity of mass ejected into the interstellar medium.

"The brightness of the source and the large collecting area of the GTC allowed us not only to detect the wind, but also to measure the variation of its properties on time-scales of minutes. The database obtained is probably the best ever observed for an object of this kind," said Teo Munoz Darias, from the Instituto de Astrofisica de Canarias (IAC) and the lead author of the study.

"This outburst of V404 Cygni, because of its complexity and because of the high quantity and quality of the observations, will help us understand how black holes swallow material via their accretion discs," said Darias.

"We think that what we have observed with the GTC in V404 Cygni happens, at least, in other black holes with large accretion discs," said co-authors of the study Charles and Jorge Casares from IAC, two of the discoverers of V404 Cygni in 1992.

V404 Cygni is a black hole within a binary system located in the constellation of Cygnus. In such systems, of which less than 50 are known, a black hole of around 10 times the mass of the Sun is swallowing material from a very nearby star, its companion star.

During this process material falls onto the black hole and forms an accretion disc, whose hotter, innermost zones emit in X-rays.

In the outer regions, however, we can study the disc in visible light, which is the part of the spectrum observable with the GTC.
The findings were published in the journal Nature.