Extreme Radiation Bursts From Stars Less Dangerous to Life Than Expected

Potsdam (Germany) Extreme radiation bursts (gamma-ray bursts) from stars, so-called superflares, have been considered to be dangerous atmospheric killers and thus there would be extremely poor conditions for life on the planets orbiting these stars. However according to a newly published study, it now shows that such eruptions pose limited danger to planetary systems as they do not explode towards the exoplanets.

As researchers from the Leibniz Institute for Astrophysics Potsdam currently report in the specialist journal “Monthly Notices of the Royal Astronomical Society”, astronomers have used optical, Time-resolved observations of the NASA planet finder “Transiting Exoplanet Survey Satellite” in collaboration with scientists from the USA and Spain and examined large superflares on young, small stars (red dwarfs) with temperatures and masses lower than our own sun.

In fact, numerous exoplanets have already been discovered around this type of star – including earth-sized and earth-like planets that orbit their star within its habitable zone. The question is whether these exoplanets are actually habitable, because red dwarfs are much more active than our sun and show frequent and intense outbreaks of radiation. “These so-called flares are magnetic explosions in the atmosphere of stars that eject intense electromagnetic radiation into space. Large flares are associated with the emission of high-energy particles which hit the exoplanets around the erupting star and can change or even destroy their atmospheres.” explain the researchers.

The team have now developed a method to determine from where on the surface of the stars the flares originate. “We discovered that extremely large flares ignite near the poles of red dwarfs and not at their equator, as is typically the case with the sun. Exoplanets that move on a plane around the equator of the star, like the planets in our own solar system, could therefore be largely protected from such superflares, as they are directed upwards or downwards out of the exoplanet system. This could improve the prospects for the habitability of exoplanets around small red dwarfs. Otherwise they would be much more endangered than planets in our solar system by the energetic radiation and particles that accompany flares.” says Ekaterina Ilin from the Leibniz Institute.

The astronomers see the evidence of near-polar flares as evidence that strong and dynamic concentrations of stellar magnetic fields form near the rotation poles of rapidly rotating stars, which can manifest as dark spots and flares. The existence of such “polar spots” has long been suspected by indirect reconstruction techniques such as Doppler imaging of star surfaces, but has not directly been proven yet.

The team has now succeeded in doing this by analyzing white light flares on rapidly rotating M dwarf stars. These last long enough to be modulated in their brightness by rotating in and out on the star’s surface. The authors were able to infer the geographical latitude of the flares directly from the shape of the light curve and also showed that the detection method is equally efficient for all latitudes. “I am particularly pleased that we can finally prove the existence of the polar spots in such rapidly rotating stars. In the future, this will help us to better understand the magnetic field structures of these stars.” adds Katja Poppenhäger, head of the Star Physics and Exoplanets department.