Red dwarf stars

Red dwarf stars

  • Red dwarf stars are the most common star type in the universe
  • Red dwarf stars are the smallest, dimmer, and longest-lived stars in the universe
  • Most planets found around other stars have been found around red dwarfs
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Stars come in a variety of types. The most common type of star in the universe is the red dwarf, which is also the smallest type of star. As the smallest and least massive stars in the universe, red dwarfs are also the darkest stars in the cosmos. Although the majority of the stars closest to the Sun are red dwarfs, not a single one is visible to the naked eye. The star closest to the sun, called Proxima Centauri, is a red dwarf star, and although it’s only 4.2 light-years away, it’s not visible even with a small telescope. What are some of the characteristics of red dwarf stars?

Characteristics of Red Dwarfs

Proxima Centauri is a red dwarf star that is also the closest star to the sun. NASA

Like every other star in the universe, red dwarf stars are powered by the fusion of hydrogen nuclei at their core. Despite their lower temperatures and pressures, hydrogen fusion still occurs in the cores of red dwarf stars, albeit much more slowly than in massive stars. Interestingly, the thermal motion through a red dwarf star differs from that of other stars. In medium to massive stars, the pressure is so high that the heat generated by fusion in the core cannot be transported by convection. Rather, massive stars rely on radiation to transport heat out of their core. Because red dwarf stars experience far less pressure than their larger counterparts, heat can move by convection. This leads to a rather interesting result. Because heat can move through a red dwarf star more efficiently, less helium accumulates in their cores. As a medium to high mass star fuses hydrogen into helium in its core, the lack of convection causes helium to build up in the core. This reduces the amount of hydrogen a star can fuse, and thus reduces the length of time the star can exist. Because red dwarf stars do not experience helium accumulation in their cores, they can exist much longer than other types of stars. The most massive stars in the universe will generally have used up their hydrogen supply in less than 10 million years. Meanwhile, red dwarf stars can continue to fuse hydrogen in their cores for hundreds of billions to even trillions of years. In fact, red dwarf stars have existed for so long that every red dwarf in the universe is still considered young. The largest known red dwarfs in the Universe are only about 10% as bright as the Sun. Red dwarfs range from as little as 0.08 solar masses to 0.6 solar masses. Red dwarfs generally have surface temperatures of around 1,700 degrees Celsius.

Planets around red dwarfs

Red dwarf system
Rendering of a solar system around a red dwarf star. NASA

Scientists have confirmed the existence of over 4,000 planets around other stars. The vast majority of these planets have been found orbiting red dwarf stars. Several factors have led to the finding of so many exoplanets around red dwarfs. Inevitably, since red dwarf stars are the most common type of star in the universe, they are also orbited by most of the planets in the universe. Additionally, methods for finding exoplanets work amazingly well for finding planets near red dwarfs. The two most popular methods for detecting exoplanets are the radial velocity method and the transit method. The radial velocity method relies on detecting the gravitational pull a planet exerts on its star, with lower mass stars being more strongly attracted to their planets. The transit method relies on finding planets passing in front of their star and blocking incoming light. The dimmer the star, the easier it is to spot a planet passing in front of it.

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