Red dwarfs are the most common and long-lasting stars in the Milky Way Galaxy, where the Solar System can be found. But how hospitable are they toward the planets orbiting around them?
Researchers looked at data from NASA's Chandra X-ray Observatory and Hubble Space Telescope to assess the intensity and frequency of high-energy flares from one nearby red dwarf, SciTech Daily reported.
They focused on Barnard's Star, one of the closest stars to Earth at a distance of six light-years away. At the age of ten billion, Barnard's Star is still very active and has the potential to be destructive for the atmospheres of its nearby planets that orbit around it.
A Target For Planet-Hunting
According to Space.com, red dwarfs make up the largest population of stars in the galaxy. But they could not be easily spotted because they are too dim to be seen with the naked eye. Through their limited radiance, they extend their lifetimes which are longer than other stars and the Sun in the Solar System.
Scientists believe that 20 out of 30 stars near Earth are red dwarfs, with the closest one is the Proxima Centauri. It is about 4.22 light-years from Earth, and the closest star other than the Sun.
The "red dwarf" term is used not only to describe a single star. The term is often used to call the coolest objects, like the true dwarfs K and M dwarfs, as well as brown stars which are referred to as "failed stars." This is due to their inability to sustain hydrogen fusion within their cores.
Astronomer Michaël Gillon of the University of Liège in Belgium told Space.com that "There is no true definition of red dwarfs." The term "generally refers to dwarf stars with a spectral type ranging from K5V to M5V," Gillon added.
Many red dwarfs have been found with planets orbiting them, which scientists have easily detected because of their dim light. It also made red dwarfs a popular target for planet-hunting.
How Hospitable Are Red Dwarfs?
SciTech Daily reported that scientists used the data from the Chandler and bubble to know how hospitable are red dwarfs toward the planets that orbit around them.
Looking at Barnard's Star as an example to study how flares from an old star could affect any planet orbiting it, they found that the X-ray flare uncovered by Chandra in June 2019 and the observations astronomers took using the bubble in March 2019 revealed two UV high-energy flares.
The two observations were seven hours long and show X-ray or UV brightness. In other words, Barnard's Star unleashes potentially destructive flares 25% of the time. The authors then looked at what these destructive flares could be doing to rocky planets orbiting around the habitable zone.
According to NASA Exoplanet Exploration, a habitable zone is a distance from a star at which liquid could be present on the surface of orbiting planets.
The team said that repeated onslaught of flares in the habitable zone for millions of years could have eroded the atmospheres of the planet even after being regenerated. Energetic radiation from the flares produced by the red dwarf could sweep away the regenerated atmosphere, reducing the planet's chance of supporting life.
Scientists are studying other red dwarfs to compare Barnard's Star if its behavior is typical in all red dwarfs. They published their study, "The High-energy Radiation Environment around a 10 Gyr M Dwarf: Habitable at Last?" in The Astronomical Journal.
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