Image shows an artist’s impression of a black hole, similar to V404 Cyg, devouring material from an orbiting companion star. Credit: ESO/L. Calçada
Violent red flashes, lasting just fractions of a second, have been observed during one of the brightest black hole outbursts in recent years. June 2015, a black hole called V404 Cygni underwent dramatic brightening for about 2 weeks, as it devoured material that it had stripped off an orbiting companion star. V404 Cygni, which is ~7,800 light years from Earth, was the first definitive black hole to be identified in our Galaxy and can appear extremely bright when it is actively devouring material.
The astronomers associated the red colour with fast-moving jets of matter that were ejected from close to the black hole. These observations provide new insights into the formation of such jets and extreme black hole phenomena.
Dr P. Gandhi said: “The very high speed tells us that the region where this red light is being emitted must be very compact. Piecing together clues about the colour, speed, and the power of these flashes, we conclude that this light is being emitted from the base of the black hole jet. The origin of these jets is still unknown, although strong magnetic fields are suspected to play a role. “Furthermore, these red flashes were found to be strongest at the peak of the black hole’s feeding frenzy. We speculate that when the black hole was being rapidly force-fed by its companion orbiting star, it reacted violently by spewing out some of the material as a fast-moving jet. The duration of these flashing episodes could be related to the switching on and off of the jet, seen for the first time in detail.”
Due to the unpredictable nature and rarity of these bright black hole ‘outbursts’, astronomers have very little time to react. Eg V404 Cygni last erupted back in 1989. V404 Cygni was exceptionally bright in June 2015.
Each flash was equivalent to the power output of ~1,000 suns. And some of the flashes were shorter than 1/40th of a second – 10X faster than the duration of a typical blink of an eye. They used ULTRACAM fast imaging camera on William Herschel Telescope, Canary Islands. ULTRACAM can capture high frame-rate ‘movies’ of astronomical targets, in 3 colours simultaneously thus the flashes were seen as red.
Dr Gandhi concluded: “The 2015 event has greatly motivated astronomers to coordinate worldwide efforts to observe future outbursts. Their short durations, and strong emissions across the entire electromagnetic spectrum, require close communication, sharing of data, and collaborative efforts amongst astronomers.” http://mnras.oxfordjournals.org/content/early/2016/03/14/mnras.stw571 http://www.alphagalileo.org/ViewItem.aspx?ItemId=162123&CultureCode=en
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