Increase in Radius when a Star becomes a Red Giant

In summary, the conversation was about the life cycle of a star, specifically the red giant phase and how to determine the factor by which its radius will increase. The expert explained that this depends on the star's mass and chemical composition, making it a complex problem. They provided a resource for looking at the evolution of different stars and shared that most of the red giant phase has a log_R = 2.24, which is about 175 times the current solar radius. This answered the original question and the person was satisfied with the information.
  • #1
Madi Araly
19
1
Hi there,
I have a question regarding the life cycle of a star. I know that when entering the red giant phase of a star's life, its radius/overall size will increase dramatically, but I was wondering if there's a basic way to determine the factor it will grow by during this process.

I've seen predictions for our Sun's expansion range from 100x its current radius to 200x its current radius, but the considerable difference between these two measurements left me skeptical.

Is there a formula to determine (even an approximation of) what a star's radius as a red giant may be?
 
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  • #2
You might want to start here:
https://en.wikipedia.org/wiki/Stellar_evolution

The precise evolutionary track of a star depends quite sensitively on its mass and chemical composition (which in turn determine what types of nuclear reactions occur in the star (which in turn determine the energy output of a star (which in turn determines the star's hydrostatic equilibrium (which in turn determine the size of the star)))). So it's not a terribly straightforward problem. Maybe there's a simple formula for certain cases, but I don't know it.
 
  • #3
The http://mesa.sourceforge.net/assets/movies/1M_pre_ms_to_wd.mov is a great resource for looking at how stars of different masses and compositions evolve. http://mesa.sourceforge.net/assets/movies/1M_pre_ms_to_wd.mov has a movie of the evolution of a star like the sun. The radius changes a lot over time, which probably explains the different numbers you are seeing.

According to that MESA movie, most of the the red giant phase has a log_R = 2.24, which is about 175 times the current solar radius.
 
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Likes Madi Araly
  • #4
phyzguy said:
The http://mesa.sourceforge.net/assets/movies/1M_pre_ms_to_wd.mov is a great resource for looking at how stars of different masses and compositions evolve. http://mesa.sourceforge.net/assets/movies/1M_pre_ms_to_wd.mov has a movie of the evolution of a star like the sun. The radius changes a lot over time, which probably explains the different numbers you are seeing.

According to that MESA movie, most of the the red giant phase has a log_R = 2.24, which is about 175 times the current solar radius.

This is just what I was looking for, thank you!
 

Related to Increase in Radius when a Star becomes a Red Giant

1. What causes a star to become a red giant?

As a star runs out of hydrogen in its core, it begins to fuse helium to produce energy. This process causes the core to contract and the outer layers of the star to expand, eventually leading to the star becoming a red giant.

2. How much does a star's radius increase when it becomes a red giant?

The exact amount of increase in radius varies depending on the size of the star, but on average, a star's radius can increase by a factor of 10 or more when it becomes a red giant.

3. What happens to a star's temperature when it becomes a red giant?

As a star's outer layers expand and cool, its surface temperature decreases. This is why red giants appear red, as they emit more red and infrared light than blue and ultraviolet light.

4. How long does it take for a star to become a red giant?

The process of a star becoming a red giant can take millions to billions of years, depending on the size of the star. For example, a star like the Sun is expected to become a red giant in about 5 billion years.

5. What happens to a star's lifespan when it becomes a red giant?

When a star becomes a red giant, it has entered the final stages of its life. This phase can last for millions of years before the star eventually dies and sheds its outer layers, leaving behind a dense core known as a white dwarf.

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