A star arrives on the main sequence after it starts hydrogen burning in its core and remains there throughout its core-hydrogen-fusion phase. A star's position and length of stay on the main sequence depend critically on mass. The most massive stars – the hot, blue-white O stars and B stars – occur to the upper left and have main-sequence lifetimes of only a few million or tens of millions if years. The least massive, hydrogen-burning stars, the red dwarfs, sit to the lower right and may remain on the main sequence for hundreds of billions of years.
Related category STELLAR ASTROPHYSICS
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