‘Superflares’ may make it hard for life to begin around dwarf stars
Powerful stellar eruptions could pose a serious challenge to the origin and evolution of life around the universe. Such outbursts throw off large amounts of ultraviolet (UV) radiation, which is not only directly harmful to life as we know it, but can also strip away the atmospheres of relatively close-orbiting planets. These issues are especially pronounced for worlds circling red dwarfs.
Red dwarfs are more active than Sun-like stars, especially when they’re young. Because each red dwarf is so dim, their ‘habitable zone’ is much closer in. “We found planets orbiting young stars may experience life-prohibiting levels of UV radiation, although some microorganisms might survive,” said Ward Howard, a doctoral student in the Department of Physics and Astronomy at the University of North Carolina (UNC), Chapel Hill.
Howard and his colleagues measured the temperatures of 42 superflares emitted by 27 red dwarfs. They did so by analysing observations made simultaneously by the Evryscope, an array of small telescopes at the Cerro Tololo Inter-American Observatory in Chile, and NASA’s Transiting Exoplanet Survey Satellite, which has been hunting for alien worlds from Earth orbit since 2018.
These observations were obtained every two minutes, allowing the scientists to get an extremely detailed temperature profile across the brief life of the red-dwarf superflares, which typically emit most of their UV radiation during a 10- to 15-minute-long peak. Temperature is strongly correlated with UV emission, so the researchers were then able to estimate the radiation loads imposed by the outbursts.