No one lives in the neighborhood of red dwarfs.

No one lives in the neighborhood of red dwarfs.

Red dwarfs are small stars – their mass and diameter are less than half those of the Sun – relatively cold. 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 may be liquid water – which has sparked speculation about the possibility of life on the worlds. that orbit them. But research published in The Astronomical Journalbased on data collected by NASA’s Chandra X-ray Observatory and the Hubble Space Telescope, indicates that most red dwarf stars create hellish environments.

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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 for 25% of the time this red dwarf emits powerful bursts of high-energy ultraviolet and X-rays that would erode the atmospheres of any nearby planet or burn it. This was already known to be the case for the youngest red dwarfs, but not for the oldest 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.

Smaller stars have a longer life than larger stars. Although stars like the Sun have a lifespan of about 10 billion years, even the oldest red dwarf stars have not yet exhausted their internal reserves of hydrogen. The heaviest red dwarfs have lifetimes of tens of billions of years; the smallest have a lifespan of trillions of years. By comparison, the universe is only 13.8 billion years old. 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 being recirculated from the outer regions to the core. Stars like the Sun are not fully convective and therefore burn only 10 percent of their hydrogen found in their cores. When that hydrogen runs out, such stars will expand enormously as they begin to burn hydrogen in a shell surrounding their helium cores. Red dwarfs, however, due to convection, are completely efficient and will burn their entire supply of hydrogen. They will then get hotter and smaller, becoming blue dwarfs and eventually ending their lives as white dwarfs.

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Due to its low luminosity, a red dwarf’s habitable zone (the region near a star where liquid water can be found on a planet’s surface) is very close to the star. A planet in that region would orbit the red dwarf every few weeks and would therefore 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.

Red dwarfs were known and studied long before they were given the specific name “red dwarfs.” However, the term “red dwarf” is attributed to Ejnar Hertzsprung, a Danish astronomer, who first used it in the 1910s. The systematic study and classification of stars was accomplished through the joint work of two astronomers, one the aforementioned Ejnar Hertzsprung and, the other, Henry Norris Russell. They established that stars can be classified according to their luminosity and surface temperature in a diagram known as the “Hertzsprung-Russell diagram” (HR).

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