Astronomy - Main sequence and red giants

[tosv]

What is the main reason why there are so many more stars in the Main sequence in comparison with the number of red giants?

 

[Drakkith]

I'd guess that the main sequence for moderate-low mass stars takes billions of years while the red giant phase is much much shorter. On the order of hundreds of millions to a billion or so years at most I think.

 

[twistedspark]

I'd agree with Drakkith on that point, plus not all main sequence stars will ever be red giants. They have to be born with 0.5 to 10 Solar masses worth of matter, or have it added to them by a companion during their lives. Akin to finding a four leaf clover on one specific day of the year.

 

[tosv]

Thanks for your replies!

I think my question have been answered now.

 

[pmacias]

The main reason for the larger number of stars in the main sequence compared to red giants is due to their different stages of evolution. Stars in the main sequence are in the early stage of their life cycle, where they are fusing hydrogen into helium in their core, releasing a large amount of energy and emitting visible light. This stage can last for billions of years, making it the longest phase in a star's life.

On the other hand, red giants are in the later stage of their life cycle, where they have exhausted their core's hydrogen fuel and have started to fuse helium into heavier elements. This fusion process causes the star's outer layers to expand, making it appear larger and cooler, hence the name "red giant." This phase is relatively short, lasting only a few million years.

Therefore, the large number of stars in the main sequence is a result of the long duration of this stage in a star's life. As stars age and move into the red giant phase, their numbers decrease, making them less common in the universe. Additionally, some stars may not even reach the red giant phase, as they may have lower masses and do not have enough fuel to undergo this expansion.

Overall, the difference in the number of stars in the main sequence and red giant phase is primarily due to the difference in their lifetimes. This highlights the importance of studying the main sequence, as it represents the most common and stable stage of a star's life.