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10 facts about red dwarfs


One day, the universe has to come to an end, and the last star will stop shining and die. It will probably be a red dwarf. Unlike the other celestial bodies that have clear classification standards, red dwarfs fall into a variety of luminosities, masses and fusion activities, making them really interesting to study. They are also considered our best bets to find life forms outside of our solar system. The term “red dwarf” was first coined in 1915, but doesn’t actually hold a clear meaning, astronomically speaking.  The appellation was set only to distinguish them from their cousins, the blue dwarfs. So what do we know about red dwarfs, and what makes them our last hope for survival?

1.    Red dwarfs are little stars

To fully understand why red dwarfs are classified as stars, we first need to comprehend what makes any other star a star. With so many bodies out there in the universe, astronomers struggled to trace down a separating line between what could possibly be a really enormous planet, or an excessively small star. Dupuy finally solved the puzzle and broke it down to a single property: the mass. Dupuy stated the following: “Mass is the single most important property of stars because it dictates how their lives will proceed”. Obviously, there is a mass limit that separates stars from planets. This mass limit permit nuclear reactions that continuously converts hydrogen atoms into helium in the core of the star, thus resulting in its brightness. “Below this limit there's not to replenish the energy that's constantly being radiated into space," as Dupuy explained. "Objects with a given mass below this limit would simply cool forever."
Let’s now return to our red dwarfs. They are from 7 to 50% of the mass of our sun. The fact that the sun is considered by astronomers as an average star, in the matters of mass, makes red dwarfs look pretty small, not that much bigger than the planet Jupiter, barely crossing the mass limit defined by Dupuy. In fact, red dwarfs are right in the verge of being stars at all, and that’s exactly why they are called dwarfs. Any less than their actual mass and they would be brown dwarfs, or in other friendly words, failed stars, not able to perform nuclear fusion. Brown dwarfs lie right between stars and planets, in astronomical classification.

2.    Red dwarfs are dim

Do not be fooled by the appellation “red dwarfs”. While red usually refers to fire, light, brightness, red dwarfs are actually dim and not so luminous. So why on Earth do we call them red? Have astronomers gone mad? In fact, there is quite a strong reason why we do so, and that’s because they are actually red. Remember, red dwarfs are not very hot compared to other stars like our beloved sun, and yet they are red. To solve this riddle, think of fire. As known, the base of the fire is the hottest part, and it cools down all the way up to the top of the flame. Coincidentally, the top happens to be red whereas the bottom blue. Finally, red is not that hot and astronomers not that stupid, after all.
Being red and not very hot, red dwarfs can’t be seen by the naked eye. Ultra-modern observatories and sophisticated equipment turn out to be rather mandatory to observe one of them. 

3.    Red dwarfs are the longest-living bodies in the universe

Once again, do not be fooled by appearances. Unlike humans, where healthy and stronger people are more likely to live longer than the fragile and the dim, there is a completely different rule that dictates who should live longer up in space. In fact, it is all the other way around; the largest and most massive stars die quicker and burst into gigantic supernovas and enigmatic black holes, where red dwarfs, the smallest stars, live to what we can safely call forever, given our modest awareness of time.
As any other star, red dwarfs fuse hydrogen into helium, but instead of keeping the fused helium in the core of the star, red dwarfs are highly convective, meaning that hydrogen and helium remain mixed together, slowing the consumption of fuel -hydrogen- by a great deal, making it both dim, not very hot, not very bright, and live longer at the same time. Red dwarfs burn so slowly that the average timespan is estimated between one to ten trillion years. In comparison, the entire universe has lived only for 13.75 billion years, the thing that make all the red dwarfs still babies and in the early state of their development. The sun is estimated to die in one billion years, which makes red dwarfs more likely to outlive the universe.

4.    Red dwarfs outnumber all the other stars

Although it is impossible to observe a red dwarf with naked eyes, this does not imply any kind of scarcity whatsoever. All in all, astronomical observations showed that, at least 70% of the total number of stars in the universe are actually red dwarfs. Further, it is believed that 20 out of the 30 closest stars to Earth are no other than, guess what, red dwarfs.
The great importance of these little stars has risen a huge interest in studying them much more deeply, to the point of giving them names. Proxima Centauri is the designation of the closest one to the solar system, with 4.25 light-years far, followed by Bernard’s Star, a 5.978 light-years distant red dwarf, and Wolf359 with 7.86 year-light lying between it and the sun.


5.    Red dwarfs host planetary systems


If we search for planets upon which we want to put our feet, we’d better head toward red dwarfs. Yes of course, red dwarfs can be the center of complete systems. Further, they are more likely to have planets orbiting around them than standard stars. For this matter, the astronomer West declares: We now know for the first time in human history that almost every star has at least one planet, and it turns out that the red dwarfs appear to host more planets than other stars. Small planets are more abundant around small stars. The most common stars in the galaxy appear to be the most common planet hosts, including planets we could envision walking on. If you were to put money around where we would find the most habitable planet, it's likely to be around a red dwarf.”

6.    Red dwarfs are most likely not habitable


Only 5% of the red dwarfs in the milky way could be considered habitable and that for the following reasons: First, for a planet to be life-friendly, it must remain in the habitable zone. Astronomers call habitable zone the area around a star where water could hold its liquid form. However, even if a planet happens to be in this zone, it needs to be much closer to the red dwarf than Earth is to the sun, since the red dwarf is smaller, less hot and less bright.
And then, two other problems rise. First, if a planet was this close to a star, it would be tidally locked, meaning that while the planet orbits the red dwarf, it will keep the same side facing the star, resulting in a continuous hot day on one face, and a perpetual icy night on the other. Second, this small distant separating the planet from the star will make water evaporate completely, and the heat should alter the planet, sealing it to the same fate as Venus, a hot burning hell.

7.    Red dwarfs vary in their energy output

Red dwarfs are far more variable, violent and unstable than normal stars. They can output their emitted energy in many different ways. Red dwarfs can be covered by star spots that can dim the emitted light by up to 40%, for months in a row. At other times, the energy could take the form of gigantic burning flames, known as solar flares, that can make the star double its brightness in a matter of minutes. This dangerous phenomenon can be very damaging for life and planets’ atmosphere.
Nevertheless, astronomers estimate that a red dwarf flaring period is only the first 1.2 billion years of its existence. So, if a planet happens to be in the habitable zone, though far enough to avoid tidal locking of a red dwarf after its flaring phase, life can be possible up there. Even writers and movie producers are optimistic about the perspective of life forms in red dwarf systems, as the iconic superman is thought to come from Krypton, orbiting a tar called Rao, a red dwarf!

8.    Red dwarfs can help understand cosmology

Given their very long lifespan, and the astonishing snail speed with which they burn their fuel, the mass of red dwarfs hardly decreases. In comparison with standard stars, the mass of the dwarfs feels pretty much constant and not evolving through time at all. This interesting property allows humans to learn, or at least estimate the mass limit at which more massive stars derail off the main sequence, and thus calculate the age of star clusters.
They might also help us understand how stars form, how the universe will be like after the death of our sun, and more importantly answer the big question: Are we alone in the universe?

9.    All red dwarfs contain metals

All known red dwarfs contain metals. Astronomically speaking, metals are elements heavier than Hydrogen and Helium. They form due to the fusion of lighter elements giving Carbon, Oxygen up to Iron. This is rather strange and defy some physics rules and properties. Given the slow motion of red dwarfs and the relatively little time of the universe existence, our beloved dwarfs should not contain any element heavier than Helium since it requires a certain amount of speed far greater than what red dwarf elements react with. To this day, no metal-proof red dwarfs have been found, and the mystery always continue to elude humanity’s brightest minds.

10.                      Everything has to come to an end, even red dwarfs

Everything mentioned about red dwarfs and them being humanity last hope after the sun burst is quite beautiful in its own terms, but everything has to die at some point, even red dwarfs.
After what seems like trillions of years, the life of the last star in the universe will come to an end as it blasts in a final show, closing off the curtains. When a red dwarf consumes up all its hydrogen, it will become what we call blue dwarfs, burning up completely. Then it transforms into white dwarfs, very dense bodies of the size of Earth, that mainly consist of Helium atoms. With the absence of any source of energy, white dwarfs will cool down extremely slowly to finally enter its final phase: black dwarfs.

 By Yacine GACI

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