The HR diagram sort stars according to their colour and size. They show 3 distinct star types. The spectral classes covered by the HR diagram are as follows, from hottest to coldest: O, B, A, F, G, K, and M. The main types of stars covered by the spectral classes classification system are giants and the main sequence stars.
Giant stars are comprised of blue giants, red giants, blue hypergiants and red supergiants. Main sequence stars are made of blue stars, yellow dwarfs, orange dwarfs and red dwarfs. Dead stars are comprised of white dwarfs, neutron stars and black holes. Brown dwarfs do not have enough hydrogen in their core to become a real star but emit their own infrared light to not be called a planet.
Blue stars on the main sequence are on spectral classes O and B. They can live up to 40 million years, while yellow dwarfs, like our Sun, live up to 17 billion years, but are on spectral class G. Orange dwarfs are on spectral class K and live up to 30 billion years, which short compared to a red dwarf's lifespan - 10 trillion year! However, red dwarfs are dim and are on spectral class K. They are also the most common type of star.
Blue giants are on spectral classes O, B and A, and they live up to 100 million years. However, blue hypergiants can only live up to 10 million years, so any blue hypergiants that existed when dinosaurs existed are probably black holes now. On the other end of the spectrum, red giants are stars which evolved out of the main sequence. They are stars beginning to die. They live up to 2 billion years after first becoming a red giant, and are on spectral classes M and K. Stars in the main sequence with more than 10 solar masses turn into a red supergiant instead, and once turned into a red supergiant, will last another 200 million years. They are on spectral classes M and K.
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| Betelgeuse, a red supergiant. Credits to ALMA/O’Gorman/P. Kervella. File under CC BY 4.0. |
I wanted to learn more about dead stars, and I enjoyed learning spectral classes.
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