During a two week long outburst last summer, a black hole located approximately 7,800 light years from Earth gave off a series of violent red flashes as it consumed material stripped from an orbiting companion star, researchers from the University of Southampton have discovered.
The black hole in question, V404 Cygni, underwent one of the brightest black hole outbursts in recent years last June, and according to Dr. Poshak Gandhi, associate professor and STFC Ernest Rutherford Fellow in the university’s Astronomy Group, and his colleagues reported in the latest edition of the journal Monthly Notices of the Royal Astronomical Society.
V404 Cygni, the first definitive black hole to be confirmed in the Milky Way, can appear to be extremely bright when devouring material, the study authors explained. During its two week stretch of activity in June 2015, it emitted red flashes that lasted a fraction of a second each as it ejected material that it was unable to swallow, they added.
Each of the flashes had brightness equal to the power output of nearly 1,000 suns, and some were less than 1/40th of a second in length, or nearly ten times faster than it normally takes a human to blink his or her eyes. The astronomers believe that the flashes’ red color was linked to the rapidly moving jets of matter ejected from close to the black hole.
The red flash in question (Credit: University of Southampton)
Outburst was the brightest event of its kind in many years
The observations, which were captured using the ULTRACAM fast imaging camera instrument equipped to the William Herschel Telescope in the Canary Islands, may improve our knowledge of how these jets form and other extreme characteristics of black holes, Dr. Gandhi said.
“The very high speed tells us that the region where this red light is being emitted must be very compact,” he explained. “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,” Dr. Ghandi added, “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.”
The unpredictable nature of black hole outbursts presents a challenge for astronomers, who must quickly respond when such an event begins if they hope to study it. As an example, V404 Cygni had not erupted since 1989 when it did so last June, and the researchers were fortunate enough to monitor what turned out to be one of the brightest black hole outbursts in several years.
“The 2015 event has greatly motivated astronomers to coordinate worldwide efforts to observe future outbursts,” said Dr. Gandhi. “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.”
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Image credit: ESO/L. Calçada
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