Most of the stars on the Hertzsprung-Russell (HR) diagram are classified as main sequence stars. Within the main sequence, the most common type of star is the main-sequence red dwarf, which is a cooler, smaller, and less luminous star compared to others. Red dwarfs make up about 76% of the main sequence stars, making them the dominant population on the HR diagram. These stars fuse hydrogen into helium in their cores, just like the Sun, but have lower masses and temperatures.
Main Sequence Stars
- The main sequence is a continuous band on the HR diagram where stars fuse hydrogen in their cores.
- About 90% of stars, including our Sun, lie along this main sequence band.
- Stars range from hot, luminous blue stars (upper left on the HR diagram) to cool, dim red dwarfs (lower right).
Red Dwarfs
- Red dwarfs are the smallest and coolest main sequence stars.
- They burn hydrogen slowly, allowing them to have very long lifetimes.
- They are so faint that most are not visible to the naked eye.
- Red dwarfs constitute the majority of stars in the universe and thus dominate the HR diagram.
In summary, the majority of stars on the HR diagram are main sequence stars, with most of those being red dwarfs, the most common stellar type in the universe.
