What is the difference between a brown dwarf and a red dwarf?

Brown dwarfs and red dwarfs are both small, cool stars, but they differ in a few key ways. Brown dwarfs are often referred to as 'failed stars' because they are not massive enough to sustain nuclear fusion in their cores, which is what powers the sun and other stars. Red dwarfs, on the other hand, are fully-fledged stars that are just smaller and cooler than the sun.

The primary difference between the two is their mass. Brown dwarfs have a mass that is between that of a giant planet and a small star (less than about 0.08 solar masses), while red dwarfs have a mass that is less than about 0.5 solar masses. This difference in mass means that red dwarfs are able to sustain nuclear fusion in their cores, while brown dwarfs are not.

Another difference between the two is their temperature. Brown dwarfs have temperatures ranging from about 1,000 to 2,500 Kelvin, while red dwarfs have temperatures ranging from about 2,500 to 3,500 Kelvin. This difference in temperature is due to the fact that red dwarfs are able to sustain nuclear fusion in their cores, which produces heat and light.