For a few minutes, the superflare's X-ray brightness outshone both stars' total luminosity in all wavelengths, researchers said. The eruption's temperature reached 360 million degrees Fahrenheit (200 million degrees Celsius) — about 13 times hotter than the sun's core.
But DG CVn wasn't done yet, firing off a number of other flares over the next 11 days, with each one being a bit weaker than the last. X-ray emission from the system finally returned to baseline levels 20 days after the April 23 event.
DG CVn's sustained activity surprised scientists.
"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 Drake, who gave a presentation about the DG CVn superflare in August at a meeting of the American Astronomical Society’s High Energy Astrophysics Division. "This was a very complex event."
Both of the stars in the DG CVn system are about one-third as massive as the sun. They orbit about 3 astronomical units from each other — too close for Swift to tell which one of them was responsible for the big flares this year. (One astronomical unit, or AU, is the average distance from Earth to the sun — about 93 million miles, or 150 million kilometers).
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