Red Dwarf Stars

They may have the word dwarf in their name, but red dwarf stars are anything but small. They are the most common and longest-lived stars in the universe. Red dwarfs typically have a mass of between 7.5% and 40% of the Sun. Though not as large as the Earth's Sun, they are still large, but the largest only emit between 10% of the Sun's light and the smallest have just one ten-thousandth of the Sun's luminosity.

They are the largest population of stars in the galaxy and are too dim to be seen with the naked eye from Earth. Because of their limited brightness, the red dwarfs have extremely long lifetimes, much greater than the Sun. In fact, compared to the 10-billion-year lifetime of sun-like stars, most red dwarfs will last trillions of years.

Scientists believe that out of the 30 stars nearest to Earth, about 20 of them are red dwarfs. The closest star to the Sun is a red dwarf called Proxima Centauri. Red dwarfs are frequently applied to the coolest objects in space and do not always refer to a single kind of star. They include K- and M-dwarfs, which are true stars, and brown dwarfs which are often referred to as 'failed stars' because they do not sustain hydrogen fusion in their cores. There is not necessarily a true definition of red dwarfs.

Nevertheless, red dwarfs form like other stars. A cloud of dust and gas is pulled together by gravity and then begins rotating. The material clumps at the center and when it reaches a critical temperature, fusion begins. The lowest temperature reached by red dwarfs is about 6,238 degrees Fahrenheit and the highest temperatures reach 9,900 degrees Fahrenheit.

Because they burn dimmer, they burn through their supply of hydrogen less rapidly resulting in their longer lifespan. Because cool stars and brown dwarfs are so dim, they are often difficult to classify when they are first discovered. Astronomers study the atmosphere of the objects they find to measure its temperature.

Many red dwarfs in the galaxy have also been found with planets surrounding them. For many years, scientists believed red dwarfs would be unfit for habitability meaning liquid water could not form on one of the planets. However, new research has shown that some planets could develop in ways that would potentially allow life to evolve. Due to this new discovery, and because red dwarfs make up more than three-quarters of the stars in the galaxy, the possibilities for the evolution of life in the universe is increased. In 2010, a planet named Gliese 581g was called the first potentially habitable alien planet because it is near a red dwarf.

Though the red dwarfs live a long time, like all other stars, they will eventually burn through their supply of fuel. When this happens, the red dwarfs become white dwarfs or dead stars that no longer undergo fusion at their core. Later, the white dwarfs become black dwarfs when all the heat is radiated away.

The Earth's Sun will become a white dwarf in a few billion years, but the white dwarfs will take trillions of years to burn through their fuel. This is much, much longer than the age of the universe which is less than 14 billion years old. Though very small, the red dwarfs will be around significantly longer than any of the other stars in the universe.