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Q & A: Formation of a Red Giant

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Most recent answer: 10/22/2007
Q:
How is a Red Giant formed and how long does it take for a star to reach the Red Giant stage?
- Laura (age 15)
Pioneer High School, Ann Arbor Michigan US
A:
Laura,

A Red Giant star is formed when a star like our sun, or one larger, runs out of its hydrogen fuel. Inside a star, hydrogen atoms are combined together to form helium atoms. This process creates the energy that the star needs to resist the force of gravity that is trying to crush the star together, and also causes the star to light up.

Once all of the hydrogen has been turned into helium (after about 5 to 10 billion years, depending on the size of the star) there is no longer energy keeping the star from collapsing, so gravity takes over and pulls the star into itself. But the star only collapses so far that the helium atoms can begin to combine into carbon atoms. This process now provides enough energy to stop the star from collapsing and actually pushes the outermost layers of the star out, making the star much larger than it origianlly started. The star is now a Red Giant.

Tim

(published on 10/22/2007)

Follow-Up #1: More on red giant stars

Q:
Do stars like our sun become larger when losing hydrogen or become smaller when losing it and then eventually collapse into a red giant?
- Michael (age 14)
Olney, MD, USA
A:
Hi Michael,
We thought we had answered the question but perhaps we didn't do a good job.
I suggest you take a look at the excellent wikepedia article that does better.


LeeH

(published on 10/22/2007)

Follow-up on this answer.