Where's the hurry? We have all the time in the world!
*This series of posts are an homage to the Choose your own adventure book series, which my Earthling alter-ego so much enjoyed in her youth.
The interior of a red dwarf. Credit: NASA/CXC/M. Weiss
It was difficult to choose among all the stars in display, but in the end, you took home the little red dwarf. You may not have been very original (about 70% of the stars in your neighbourhood belong to this type), but you can tell the advantages: It does not only require less space (sizes come from about one half of the Sun's radius to about that of planet Jupiter), but its relatively low temperature (less than 3,300 degrees Celsius) makes it easier to manipulate as well. Moreover, you find its moderate glow (only 10% of that of a Sun-like star) very relaxing and intimate.
According to the salesperson, this is also a robust, long-lasting star. All thanks to its fully convective interior, which is very efficient in mixing the gas. Therefore, the helium resulting from the nuclear fusion does not accumulate in the core, allowing the star to burn a higher percentage of hydrogen than stars of higher masses. It also helps that it has such a low mass (less than 25% of the Sun's), so that the need for fuel to balance gravity is not as high as with other stars.
(Admittedly, it was also the cheapest type of star in the store, but that is secondary)
A flaring red dwarf may threaten life on surrounding planets. Credit: NASA, ESA and D. Player (STScI)
Playing with planets
You have arranged some planets around your little star. However, it is being quite hard to find a way to cultivate life forms in your planetary system. Although your star seems to have a special attachment for rocky planets, which is a good sign, its low surface temperature forces you to place a planet very close to it in order to get liquid water on the surface. This is tricky, because you do not want the planet and the star to crash!
The solution you have found is that the planet is always showing the same face to the star. This means that one side of the planet is always in daylight, and the other lies in a perpetual night... Whether this is good for life or not, you are not sure. After all, life needs a source of energy, but nobody said that the only possible source is starlight. What is clear, though, is that one side of the planet is very cold in comparison to the other. You are now experimenting with the atmosphere to see if you can find a way to make heat circulate.
Another reason for concern is the star's temperament. It may seem peaceful, but your little red dwarf has flares of character from time to time. Being so close to it, you fear that this may negatively affect your potentially habitable planet. Your only hope is that this activity decreases as the star ages.
After trillion of years, your star will become a helium white dwarf, and it will look similar to this artist's illustration. Credit: ESA and NASA
An eternal star?
And talking about aging... Millions, billions of years go by, and your star still looks pretty much the same. The salesperson didn't exaggerate at all about its durability!
Word of mouth says, your star will eventually use up all its hydrogen and contract to become a helium white dwarf... An even smaller ball of gas, hotter and bluer, which will then cool down for a long, long time.
However, when you ask other star owners you know, the answer is always the same: Nobody has ever seen a red dwarf die. It looks like the Universe is still too young for that!