Red and Brown Dwarf Stars
A dwarf star is a star that is relatively small and dim. Astronomers describe a stars’ luminosity in comparison to the brightness of the sun. Those much more luminous are giants, those much dimmer are dwarves. Additionally, astronomers graph stars based on their luminosity and temperature. This is on a Hertzsprung-Russell diagram, which shows us where red and brown dwarf stars place compared to other stars.
Red Dwarf Stars
Red dwarf stars are small stars as they are smaller than half the size of our Sun. They are cooler than most stars and also fainter. This means they are found on the bottom of the Hertzsprung-Russell diagram, near both axis. Red dwarf stars are extremely common and are found all around the Milky Way Galaxy.
Formation and Characteristics
Red dwarf stars form like other main-sequence stars. In simple terms, a clump of dust and gas are exposed to heat and fusion, and a star is formed. The low temperature of these stars means that they burn through hydrogen slower than a massive star like the Sun. Their lifetimes may extend to trillions of years. This is far longer than the lifetime of Sun-sized stars.
Why are red dwarf stars red?
Because red dwarf stars only burn a little bit of fuel at a time, they are not very hot compared to other stars. Think of a fire. The coolest part of the fire is at the top of the flame where it glows red. The hotter part in the middle glows yellow, and the hottest part near the fuel glows blue. Stars work the same way. Their temperature determines what color they are. Thus, we can determine how hot a star is by its color.
Brown Dwarf Stars
A brown dwarf has the same characteristics as a star but does not have enough mass for nuclear fusion. Without nuclearfusion, the star cannot glow. Brown dwarfs are not regular stars because they do not glow. However, they are not regular giant planets either.
Brown Dwarfs vs. Planets
When you look up at the night sky, it is easy to mistake a star for a planet, or vice versa. However, planets shine by reflected light and stars shine by producing their own light. Stars go through a process known as nuclear fusion. This process releases a gigantic amount of energy which causes the star to shine. Planets form from leftover particles of dust. They don’t have enough energy to produce their own light. Brown dwarf stars, although small compared to other stars, are large relative to planets.
Other Great Resources:
The Difference between Big Planets and Brown Dwarfs: https://www.universetoday.com/138338/wheres-line-massive-planet-brown-dwarf-star/
Study Tool for Dwarf Stars: https://astroquizzical.com/astroquizzical/what-different-types-of-dwarf-star-are-there-and
More on Dwarf Stars: https://www.space.com/23798-brown-dwarfs.html