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Wind 'outburst' will help scientists unlock mysteries of black holes

An intense wind travelling at 3,000km (1,864 miles) per second has been discovered coming from one of the closest known black holes to the Earth.

During observations of V404 Cygni, which went into a bright and violent outburst in June 2015 after more than 25 years of quiescence, a team of international astrophysicists found the presence of the wind of neutral material (unionised hydrogen and helium).

It is formed in the outer layers of the accretion disc, regulating the accretion of material by the black hole.

The discovery was made using the 10.4m Gran Telescopio Canarias (GTC) - the biggest optical-infrared telescope in the world, situated at the Roque de los Muchachos Observatory (Garafia, La Palma) in the Canary Islands.

The results, which are published today in Nature, show that the 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.

Professor Phil Charles, from the University of Southampton, said: "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."

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

Teo Munoz Darias, a researcher at the Instituto de Astrofisica de Canarias (IAC) and the lead author of the study, said: "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.

"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."

V404 Cygni is a black hole within a binary system located in the constellation of Cygnus which is 8,000 light years away. 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.

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