Why there are so many Main Sequence stars compared to the much smaller percentage of stars that are Red Giants and White Dwarfs?

Answer 1

For three reasons.

1) Hydrogen is the most abundant element in the universe.

2) ALL stars spend a part of their life on the main sequence because wile on the main sequence the fuel they are fusing is Hydrogen.

3) For a given mass of hydrogen, the energy output created by fusing hydrogen is the greatest of all fusible elements (i.e the elements up to Iron). Thus as stars start fusing other elements (and thereby moving off the main sequence) they burn through their fuel very quickly and either explode a supernovae or decay into white dwarfs (depending on their initial mass).

One may also note that the most common type of stars are red dwarf stars on the main sequence and this is because the rate of hydrogen fusion depends on the stars mass a really big star will only last a few million years while a small red dwarf will shine for trillions of years. Thus the big stars die quickly while the small ones last a long time so one ends up with more of them (more smaller stars may also be produced in the first place too).

Answer 2

As gravity pulls a star together in the main sequence the increased density and heat causes faster nuclear fusion of hydrogen into helium. This force tries to expand the star. But the more the star expands the slower and less powerful the fusion.

These two forces come into equilibrium until the hydrogen runs low. This takes a relatively long time. In other stages of stars life cycles they are not in equilibrium. Either the force of gravity or the expanding forces are stronger. In these cases the star contracts or expands.

There are other stable states for stars besides the main sequence. These sometimes do not last as long as the main sequence because the force keeping the star from collapsing further does not last as long. Some star states are actually more stable than the main sequance stage though. White dwarf stars will stay white dwarfs for longer than main sequence stars will stay in the main sequence.

Answer 3

Only stars that have enough mass, have a core temperature > 10 million degrees kelvin, which is when nuclear fusion occurs, the star is then said to be on the main sequence.

It will stay on the main sequence until all of the hydrogen in the core has been used up.

See related question

Answer 4

There aren't, really; it's just that the big main sequence stars are BIG and BRIGHT, and can be seen from thousands of light-years away, while a red dwarf like Proxima Centauri isn't visible from Earth, even though it is the closest star to our Sun.

The facts are that there are far more small dim red dwarf and even dimmer brown dwarf stars than there are big stars - but we can't see them without powerful telescopes.

The few big, bright stars get the attention, partly BECAUSE they are unusual.

For red giant and white dwarf stars, these are old stars near the end of their lives; they don't spend much time as "red giants" or "white dwarves".

Answer 5

Main Sequence stars are in the stable phase of their life cycle where they fuse hydrogen into helium. As a result, they stay on the Main Sequence for much longer than they do in the Red Giant or White Dwarf phases, leading to a higher abundance of Main Sequence stars. Red Giants and White Dwarfs represent later stages of stellar evolution, where stars have exhausted their hydrogen fuel and expanded or contracted accordingly.

Answer 6

Because luminosity is related to temperature

Answer 7

The lesser anthropic principle.

Expanding on that a bit: if the Sun were NOT a main sequence star, we wouldn't be around to be asking the question.

Answer 8

The main sequence is the longest period of a star's life.

Answer 9

Because they are hotter.