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How habitable are the planets that orbit the red dwarfs – the most common type of star in the galaxy?



Barnard's star red dwarf

This artist’s illustration depicts an old red dwarf like Barnard’s star (right) and an orbital, rocky planet (left). Credit: NASA / CXC / M. Weiss

  • How hospitable are the red dwarf stars, the most common and long-lived stars in our Galaxy?
  • The researchers used data from Chandra and Hubble to examine the intensity and frequency of high-energy eruptions from a nearby red dwarf.
  • Barnard’s star is one of the closest stars to Earth at a distance of only 6 light years.
  • At its age of 10 billion years, the Barnard Star is still very active and potentially destructive to the atmospheres of all the planets orbiting it.

A research study using data from NASAis the Chandra X – ray Observatory and Hubble Space Telescope gives a new idea of ​​an important question: how habitable are the planets orbiting the most common type of star in the Galaxy? The aim of the new study is the Barnard star, which is one of the closest stars on Earth at a distance of only 6 light years. Barnard’s star is a red dwarf, a small star that slowly burns its fuel supply and can last much longer than medium-sized stars like our Sun. It is about 10 billion years old, which makes it twice as old as the Sun.

The authors used Barnard’s star as a case study to learn how eruptions from an old red dwarf could affect the planets orbiting it. The artist’s illustration at the top of this page depicts an old red dwarf like Barnard’s star (right) and an orbital, rocky planet (left).

Barnard's starlight curve

Credit: X-ray light curve: NASA / CXC / University of Colorado / K. France, etc .; UV light curve: NASA / STScI;

Chandra’s research team’s observations of the Barnard star in June 2019 revealed an X-ray flash, and their Hubble observations in March 2019 revealed two ultraviolet high-energy eruptions (shown in the chart above). Both observations lasted about seven hours and both graphs show X-ray or ultraviolet brightness extending to zero. Based on the length of the eruptions and the observations, the authors conclude that the Barnard star triggers potentially destructive bursts about 25% of the time.

The team then studied what these results meant for rocky planets orbiting the habitable zone – where liquid water could exist on their surface – around an old red dwarf like Barnard’s star. Any atmosphere formed at the beginning of life on a habitable planet was probably eroded by high-energy radiation from the star during its volatile youth. Later, however, the planet’s atmosphere can regenerate as the star becomes less active with age. This regeneration process can arise from gases emitted by solid material impacts or gases emitted by volcanic processes.

The onslaught of powerful eruptions such as those reported here, which have occurred repeatedly over hundreds of millions of years, can destroy any regenerated atmosphere of rocky planets in the habitable zone. The illustration shows the atmosphere of the rocky planet, carried to the left by energy radiation from eruptions produced by the red dwarf. This would reduce the chance of these worlds sustaining life. The team is currently studying high-energy radiation from many more red dwarfs to determine if Barnard’s star is typical.

Reference: “High-energy radiation environment around 10 Gyr M dwarf: Habitable at last?” By Kevin France, Girish Duvuri, Hilary Egan, Tommy Koskinen, David J. Wilson, Alison Youngblood, Cynthia C. Froning, Alexander Brown, Julian D. Alvarado-Gomez, Zahori K. Bertha-Thompson, Jeremy J. Drake, Cecilia Garafo, Lisa Kaltenegger, Adam F. Kowalski, Jeffrey L. Linsky, RO Parke Loyd, Pablo JD Mauas, Yamila Miguel, J. Sebastian Pineda, Sarah Rugheimer, P. Christian Schneider, Feng Tian and Mariela Vieytes, October 30 2020, The Astronomical Journal.
DOI: 10.3847 / 1538-3881 / abb465

A report describing these results, led by Kevin France of the University of Colorado at Boulder, appears in the October 30, 2020 issue of The Astronomical Journal. NASA’s Marshall Space Flight Center manages the Chandra program. The Chandra X-ray Center of the Smithsonian’s Astrophysical Observatory oversees science and flight operations from Cambridge and Burlington, Massachusetts.




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