Violent Red Flashes Observed Occuring from 1st Black Hole Detected in the Milky Way

 

 

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Violent red flashes, lasting just fractions of a second, have been observed during one of the brightest black hole outbursts in recent years. In June of 2015, NASA's Swift satellite detected a rising tide of high-energy X-rays from the constellation Cygnus on June 15, just before 2:32 p.m. EDT. About 10 minutes later, the Japanese experiment on the International Space Station called the Monitor of All-sky X-ray Image (MAXI) also picked up the flare. The outburst came from V404 Cygni, a binary system located about 8,000 light-years away that contains a black hole shown in the center of the image above. Every couple of decades the black hole fires up in an outburst of high-energy light, becoming an X-ray nova. V404 Cygni, which is about 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.


In a new study published in the journal Monthly Notices of the Royal Astronomical Society, an international team of astronomers, led by the University of Southampton, report that the black hole emitted dazzling red flashes lasting just fractions of a second, as it blasted out material that it could not swallow.

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.

The inset above shows one still image of a red flash observed from the black hole V404 Cygni by the ULTRACAM fast imager on the William Herschel Telescope in the early morning hours of June 26, 2015. The flashes are incredibly short and last less than one second, with some of them being even faster than 1/40th of a second. The flashes are equivalent to a luminosity of about 1,000 times the Sun's power. The background image shows a region of the sky in the Cygnus constellation, with the Cygnus Loop supernova remnant on the bottom left. Credit: DSS2 / sky-map.org / Gandhi et al. Click through for a 6 second movie segment of the same data.

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“The very high speed tells us that the region where this red light is being emitted must be very compact," said lead author of the study Dr Poshak Gandhi, Associate Professor and STFC Ernest Rutherford Fellow in the University of Southampton’s Astronomy Group. "Piecing together clues about the color, 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. For example, V404 Cygni last erupted back in 1989. V404 Cygni was exceptionally bright in June 2015 and provided an excellent opportunity for such work. In fact, this was one of the brightest black hole outbursts in recent years. But most outbursts are far dimmer, making them difficult to study.

Each flash was blindingly intense, equivalent to the power output of about 1,000 Suns. And some of the flashes were shorter than 1/40th of a second — about ten times faster than the duration of a typical blink of an eye. Such observations require novel technology, so astronomers used the ULTRACAM fast imaging camera mounted on the William Herschel Telescope in La Palma, on the Canary Islands.

Professor Vik Dhillon, of the University of Sheffield and co-creator of ULTRACAM, said: "ULTRACAM is unique in that it can operate at very high speed, capturing high frame-rate 'movies' of astronomical targets, in three colours simultaneously. This allowed us to ascertain the red colour of these flashes of light from V404 Cygni."

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. These observations can be a real challenge, especially when attempting simultaneous observations from ground-based telescopes and space satellites."

The new work appears in 'Furiously Fast and Red: Sub-second Optical Flaring in V404 Cyg during the 2015 Outburst Peak', P. Gandhi et al, Monthly Notices of the Royal Astronomical Society, Oxford University Press, in press.

The William Herschel Telescope (WHT) is a 4.20-metre (165 in) optical/near-infrared reflecting telescope located at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands, Spain. The telescope, which is named after William Herschel, is part of the Isaac Newton Group of Telescopes. It is funded by research councils from the United Kingdom, the Netherlands and Spain.

ULTRACAM was developed by Professor Vik Dhillon of the University of Sheffield together with Professor Tom Marsh of the University of Warwick. It is supported by Science and Technology Facilities Council funding.
This research was a collaboration between the universities of Southampton, Sheffield and Warwick, together with international partners in Europe, USA, India and the UAE.

The Daily Galaxy via University of Southhampton

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