Red dwarfs are small stars – their mass and diameter are less than half that of the Sun – relatively cool. They are the most common in the Milky Way, and we have discovered quite a few exoplanets in their habitable zones – the distance from them where there can be liquid water – which has sparked speculation about the possibilities of life on the worlds. that orbit them. But research published in The Astronomical Journal , based on data collected by NASA’s Chandra X-ray Observatory and the Hubble Space Telescope, indicates that most red dwarfs create hellish environments.
Death by scorching
The observations have focused on Barnard’s star, located just 6 light years from Earth – it is one of the closest. And they have found that 25% of the time this red dwarf emits powerful bursts of high-energy X-rays and ultraviolet rays that would erode or burn the atmospheres of any nearby planet. This was already known to be the case for younger red dwarfs, but it had not been found for older ones, such as Barnard’s star. Conclusion: these celestial bodies would be hostile to life on the planets in their habitable zone, which would rule them out as an object of study in the search for extraterrestrial organisms.
The smallest stars have a longer life than the largest stars. While stars like the Sun have a lifespan of about 10 billion years, even the oldest red dwarf stars have not yet depleted their internal hydrogen stores. The heaviest red dwarfs have a lifespan of tens of billions of years; the smallest have a lifespan of billions of years. By comparison, the universe is only 13.8 billion years old. The faint red dwarfs will be the last stars to shine in the universe.
Red dwarfs will not go through a red giant phase in their evolution. Because convection occurs throughout the entire star, hydrogen is constantly recirculating from regions outside the core. Stars like the Sun are not completely convective and therefore burn only 10 percent of their hydrogen found in their cores. When that hydrogen is depleted, such stars will expand enormously as they begin to burn hydrogen in a shell surrounding their helium nuclei. Red dwarfs, however, due to convection, are completely efficient and will burn off your entire hydrogen supply. They will then get hotter and smaller, becoming blue dwarfs and eventually ending their lives as white dwarfs.
Due to its low luminosity, the habitable zone of a red dwarf (the region near a star where liquid water can be found on the surface of a planet) is very close to the star. A planet in that region would orbit the red dwarf every few weeks and thus often transit its star. Also, the transits would be quite remarkable, since the small radius of a red dwarf means that more of the star would be covered by the passing planet.
