What Is A Red Dwarf?
Red dwarf stars make up the greatest number of stars in the galaxy, but they hide away from sight in the darkness of space as they are too dim to be seen with the naked eye from Earth.
Their small radiance helps them live for incredible amounts of time, far greater than that of our sun. Scientists predict that around 20 out of 30 stars near Earth are Red Dwarf stars. The closest star to the sun called Proxima Centauri, is a Red Dwarf.
The term ‘red dwarf’ does not refer to just one type of star, it is frequently used to describe objects which are cooling, including K and M dwarfs, which are true stars, and brown dwarfs often referred to as ‘failed stars’ because they do not sustain hydrogen fusion in their cores.
According to astronomer Michaël Gillon from the University of Liège in Belgium, “There is no true definition of red dwarfs”.
‘Space’ website writer Nola Taylor Tillman says that “Red dwarfs form just like other ‘main sequence stars’. A cloud of dust and gas is drawn together by gravity and begins rotating.
The material then clumps together at the centre, it eventually reaches critical temperature and fusion begins. Red dwarfs include the smallest stars, weighing between 7.5% and 50% of the mass of the sun. Because of their reduced size, it means they burn at a lower temperature, reaching around 6,380 degrees Fahrenheit.
In comparison, the sun has a temperature of 9,900 degrees Fahrenheit. This low temperature means they are far dimmer than normal stars. Because of their lower temperature, it means they burn through their fuel much more slowly. Other more massive stars burn through only hydrogen at the core before reaching the end of their lifetimes; red dwarfs consume all their hydrogen inside and outside their core.
This lengthens the lifetime of red dwarf stars to trillions of years, far beyond the lifetime of sun type stars”.
The Habitability Of Planets Near Red Dwarfs
NASA’s editor Lee Mohon states that “The planets orbiting close to the long-lasting red dwarf stars in our Milky Way may be less hospitable than previously thought.
A recent study using NASA’s Chandra X-Ray Observatory and the Hubble Space Telescope studied the red dwarf star named Barnard’s Star, which is approximately 10 billion years old, more than twice the age of the sun.
Barnard’s star is one of the closest stars to Earth at a distance of only 6 light-years. Young red dwarfs, with ages less than a few billion years, are sources of high energy radiation, including blasts of ultraviolet light and X-rays. However, scientists know less about how much damaging radiation red dwarfs give off later in their lifetimes”.
“New observations concluded that about 25% of the time, Barnard’s star unleashes searing flares, which are thought to potentially damage the atmospheres of planets closely orbiting. It’s only known planet does not have habitable temperatures, this adds to the evidence that red dwarfs may present serious challenges for life on their planets”.
“Red dwarfs are the most common type of star, and their small sizes make them favourable for studying orbiting planets.
Astronomers are interested in understanding what the prospects are for habitable planets around red dwarfs”, said Kevin France from the University of Colorado in Boulder. “Barnard’s Star is a great case study for learning about what happens around older dwarfs in particular”.
The Hubble observations research team of Barnard’s Star revealed two ultraviolet high energy flares, and Chandra observations found an X-Ray one too. Both observations were about seven hours long. The first in March 2019, the second in June 2019.
“If these snapshots are representative of how active Barnard’s Star is, then it is pumping out a lot of harmful radiation,” said study co-author Girish Duvvuri, also of the University of Colorado. “This amount of activity is surprising for an old red dwarf.”
What Does This Mean For The Atmosphere Of Nearby Planets?
NASA’s website editor Lee Mohon states that “Any atmosphere formed early in the history of a habitable zone planet was likely to have been blasted away by high energy radiation from the dwarf star during its energetic youth. Later on, though, planets’ atmospheres may have had enough time to regenerate as the star settles down with age.
This regeneration process may occur by gasses released by impacts of solid material or gases being released by volcanic processes. The attack of powerful flares like those reported here, repeatedly occurring over hundreds of millions of years may erode any regenerated atmosphere on rocky planets in the habitable zone.
This would significantly reduce the chance of these worlds supporting life. Due to these surprising findings, the team considered possibilities for life on planets orbiting older more calm red dwarf stars.
Although planets in the traditional habitable zone may not be able to hold onto their atmospheres because of flares, astronomers can extend their searches for planets out to greater distances from the host star.
Here the doses of high energy radiation are smaller. At these greater distances, it may be possible that greenhouse effects from gases other than carbon dioxide, like hydrogen, allows liquid water to exist”.
“It’s hard to say what the likelihood is of any ‘one’ planet in any one system being habitable either today or in the future”, said University of Colorado’s Allison Youngblood.
“Our research shows one important factor that needs to be considered in the complicated question surrounding whether or not a planet can support life.
A team is currently studying the high energy radiation from many more red dwarfs to figure out whether what they found from Barnard’s Star is typical or not. “It may turn out that most red dwarfs are hostile to life,” said co-author Tommi Koskinen of the University of Arizona in Tucson.
“In that case, the conclusion might be that planets around more massive stars, like our own Sun, might be the optimal location to search for inhabited worlds with the next generation of telescopes.”
Everything Has To Come To An End
Red dwarfs may be small and dim, but they live for extraordinary lengths of time. But, eventually, they will burn through their fuel supplies. When this eventually happens, red dwarfs become white dwarfs.
Essentially fusion stops occurring at the core, therefore they become ‘dead stars’. What comes after this is ‘black dwarfs’, where they eventually radiate away all of their heat.
The sun will become a white dwarf in billions of years, however, red dwarfs will take trillions of years to burn through their fuel. This is a huge amount longer than the age of the universe. Red dwarfs may be dim and slow-burning, but they sure do win the race of survival.
Ultimately, the jury is still out on whether it’s possible for nearby planets of a red dwarf star to host life. As science and technology has progressed, we have learnt more about the nature of red dwarf stars, and although earlier in history we thought there was a very good chance of habitable planets nearby red dwarf stars.
We have learnt more recently, the surges given out by red dwarf stars in their younger years may produce catastrophic irreparable damage to the nearby planets’ atmospheres. However, what we don’t know is whether the planet’s atmospheres may regenerate over time as the dwarf star settles down. As always in astronomy, there is certainly still hope yet.
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