October 1, 2014
Superflares From A Nearby Red Dwarf Star Observed By NASA’s Swift Satellite
April Flowers for redOrbit.com - Your Universe Online
The strongest, hottest and longest-lasting sequence of stellar flares ever seen from a nearby red dwarf star was detected by NASA's Swift satellite on April 23. The first salvo from this record-setting series of flares was easily 10,000 times more powerful than the largest solar flare ever recorded from our own Sun."We used to think major flaring episodes from red dwarfs lasted no more than a day, but Swift detected at least seven powerful eruptions over a period of about two weeks," said Stephen Drake, an astrophysicist at NASA's Goddard Space Flight Center. Drake presented his findings on the "superflare" at the August meeting of the American Astronomical Society’s High Energy Astrophysics Division. "This was a very complex event."
[ Watch the Video: Swift Catches Mega Flares From A Mini Star ]
The temperature of the flare reached 360 million degrees Fahrenheit at its peak - more than 12 times hotter than the center of our Sun.
Swift observed the superflare from one of the stars in a close binary system known as DG Canum Venaticorum (DG CVn), which is approximately 60 light-years from Earth. Both stars in the system are dim red dwarfs. They are each about one-third the mass of our Sun. The stars orbit each other so closely — at approximately three times the average distance of the Earth from the Sun — that Swift was unable to determine which star erupted.
"This system is poorly studied because it wasn't on our watch list of stars capable of producing large flares," said Rachel Osten, an astronomer at the Space Telescope Science Institute in Baltimore and a deputy project scientist for NASA's James Webb Space Telescope, now under construction. "We had no idea DG CVn had this in it."
Within a 100 light-year radius of our solar system, most of the stars are middle aged, like our Sun. Around a thousand or so young red dwarfs born elsewhere drift through the region, however, giving astronomers opportunities for detailed study of the high-energy activity of young stars. DG CVn is estimated to be around 30 million years old.
Swift's Burst Alert Telescope (BAT) was triggered by the rising tide of X-rays being emitted by the superflare at 5:07 pm EDT on April 23. Within seconds, BAT was able to calculate an initial position, determine if the activity merited investigation by other instruments, and send the position of the activity to the spacecraft. The Swift spacecraft turned to capture greater detail and alerted astronomers worldwide that the superflare was in progress.
"For about three minutes after the BAT trigger, the superflare's X-ray brightness was greater than the combined luminosity of both stars at all wavelengths under normal conditions," noted Goddard's Adam Kowalski, who is leading a detailed study on the event. "Flares this large from red dwarfs are exceedingly rare."
The flares observed were extraordinary. Swift's Optical/Ultraviolet Telescope measured an increase in both visible and ultraviolet light brightness by a factor of ten. The initial flare's X-ray output outstripped even the most intense solar activity ever recorded.
The largest explosions from our Sun are classified as X class, or extraordinary, because of the level of X-ray emission. "The biggest flare we've ever seen from the sun occurred in November 2003 and is rated as X 45," explained Drake. "The flare on DG CVn, if viewed from a planet the same distance as Earth is from the sun, would have been roughly 10,000 times greater than this, with a rating of about X 100,000."
[ Watch the Video: X-Class: A Guide to Solar Flares ]
DG CVn continued to erupt for the next 11 days, with each blast becoming successively weaker, much like the aftershocks of a major earthquake. The binary system took about 20 days total to settle back to its normal level of X-ray emission.
A crucial factor to such a relatively small star producing such enormous flares is the rapid spin of the star. The spin amplifies the magnetic fields of the star. The flaring star in DG CVn rotates about 30 or more times faster than our Sun. Astronomers believe that the Sun rotated much faster in its past, but is not capable of such activity now.