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August 5, 2021
Astronomers have long suspected that superflares, bursts of extreme radiation from stars, can cause lasting damage to the atmosphere – and therefore to the habitability – of exoplanets. A new study published August 5 in the Monthly Notices of the Royal Astronomical Society reports that they pose only a limited danger to planetary systems.
“We know these are large flares, much larger than the ones we see on our own sun,†the co-author said. James davenport, Assistant Research Professor in Astronomy at the University of Washington. “Now we are seeing super-eruptions occurring at high latitudes, near the ‘poles’ of the star, which means that the bursts of radiation are not directed into the paths of orbiting exoplanets.”
Small stars actively ignite and expel particles that can alter and evaporate the atmosphere of planets in their orbit. New findings suggest that large super eruptions tend to originate from high latitudes, sparing planets that orbit the stellar equator.Leibniz Institute of Astrophysics Potsdam / J. Fohlmeister
Flares are magnetic explosions on the surface of stars that expel intense electromagnetic radiation into space. Large eruptions like super eruptions emit a cascade of energetic particles that can strike exoplanets orbiting the Blazing Star and in so doing alter or even evaporate planetary atmospheres.
Using optical observations from the Transiting Exoplanet Survey – or TESS – satellite, the team, led by astronomers from the Leibniz Institute for Astrophysics in Potsdam, studied large surges on red dwarfs, a class of young, small stars that have a lower temperature and mass than our own sun.
Many exoplanets have been found around these types of stars. A lingering question in exoplanet research is whether these exoplanets are habitable, because red dwarfs are more active than our sun and flare up much more frequently and intensely.
The team developed a method to determine the location on the surface of stars from which flares originate. The team did this by analyzing what are known as “white light flares” on rapidly rotating red dwarf stars. These types of eruptions last long enough that their brightness, as observed by TESS, varies as they rotate inside and outside the stellar surface.
“Since we cannot see the surfaces of these stars, determining the latitudes of things like hot flares and cold spots has traditionally been between difficult and impossible!” said Davenport, who is also associate director of data intensive research in astrophysics and cosmology – or DiRAC – Institute at UW. “This work combines intelligent data modeling with uniquely precise data from missions like TESS, and finds something remarkable.”
The team found rotating flares by processing the light curves of more than 3,000 red dwarf stars with TESS. Of those stars, they found four with flares large enough for their new method. The team used the precise shape of each star’s light curve to infer the latitude of the flare region and found that all four flares were occurring above about 55 degrees latitude, which is a lot. closer to the pole than the flares and spots on the surface of our sun. , which generally occur below 30 degrees of latitude. The team also showed that their detection method was not biased towards a particular stellar latitude.
These findings, even with just four eruptions, are significant: If the eruptions were evenly distributed over the stellar surface, the odds of finding four eruptions in a row at such high latitudes would be about 1 in 1,000.
This has implications for the models of the magnetic fields of stars and for the habitability of the exoplanets that orbit them.
“We have found that extremely large flares are launched near the poles of red dwarf stars, rather than their equator, as is usually the case on the Sun,” said lead author Ekaterina Ilin, doctoral student at Leibniz. . “Exoplanets that orbit in the same plane as the star’s equator, like the planets in our own solar system, could therefore be largely protected from these super-eruptions, because they are directed up or down outside. of the exoplanet system. This could improve the prospects for the habitability of exoplanets around small host stars, which would otherwise be much more threatened by energetic radiation and particles associated with flares compared to planets in the solar system.
The detection of these flares is further evidence that strong and dynamic concentrations of stellar magnetic fields, which can manifest as dark spots and flares, form near the rotating poles of rapidly rotating stars. The existence of such “polar points” has long been suspected from indirect reconstruction techniques such as Doppler imaging of stellar surfaces, but has not been detected directly until now.
“Nature tells us something important about how these typically young little stars produce magnetic fields that are much stronger than our sun,†Davenport said. “This has huge implications for how we think about the planets that orbit them.”
The co-authors are Katja Poppenhaeger, Sarah Schmidt, Silva Järvinen, Julián Alvarado-Gómez and Ilya Ilyin from the Leibniz Institute of Astrophysics in Potsdam; Elisabeth Newton at Dartmouth College; Sebastian Pineda at the University of Colorado Boulder; and Mahmoudreza Oshagh from the Canary Islands Institute of Astrophysics and the University of La Laguna in Spain. Ilin and Poppenhaeger also have appointments at the University of Potsdam. The research was funded by NASA, the German National Scholarship Foundation, the Leibniz Association and UW.
For more information, contact Davenport at [email protected].
Adapted from a Press release by the Leibniz Institute of Astrophysics in Potsdam.
Tag (s): astronomy and astrophysics • College of Arts and Sciences • Department of Astronomy • DIRAC Institute • James Davenport
