Red giant Definition and 23 Threads

A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses (M☉)) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around 5,000 K (4,700 °C; 8,500 °F) or lower. The appearance of the red giant is from yellow-orange to red, including the spectral types K and M, but also class S stars and most carbon stars.
Red giants vary in the way by which they generate energy:

most common red giants are stars on the red-giant branch (RGB) that are still fusing hydrogen into helium in a shell surrounding an inert helium core
red-clump stars in the cool half of the horizontal branch, fusing helium into carbon in their cores via the triple-alpha process
asymptotic-giant-branch (AGB) stars with a helium burning shell outside a degenerate carbon–oxygen core, and a hydrogen-burning shell just beyond that.Many of the well-known bright stars are red giants, because they are luminous and moderately common. The K0 RGB star Arcturus is 36 light-years away, and Gamma Crucis is the nearest M-class giant at 88 light-years' distance.

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  1. L

    I Expansion of a star to become a red giant

    How exactly does a star become a red giant, i.e how does its radius expand so much? When a star runs out of hydrogen to fuse into helium the star's core is essentially all helium, but the core isn't hot enough to start the triple alpha process to start fusing helium yet. So gravity takes over...
  2. jjson775

    I How Does Technetium-99 Appear in Red Giants Beyond the Iron Peak?

    Technetium 99 was detected by spectroscopy in a red giant. How did it get there if it is heavier than the “iron peak”, the upper limit for fusion?
  3. Astronuc

    I J0524-0336, surprisingly high Li concentration

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  4. Vanadium 50

    B Which star is the closest red giant to Earth according to The Guardian?

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  5. Philosophaie

    I What happens first -- Sun Red Giant or Andromeda collision?

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  6. S

    I Exploring Life & Technology In A Red Giant Sun's Sphere

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  7. O

    B Will Big Stars Turn Into Red Supergiants or Red Giants?

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  8. T

    B Why will Betelgeuse go supernova?

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  9. T

    B Why don't high mass stars expand and cool?

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  10. Madi Araly

    Increase in Radius when a Star becomes a Red Giant

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  11. 2

    Difference between a red giant and red supergiant?

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  12. JohnPrior3

    Death of Sun: Habitable Zone & Timeline

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  13. 1

    Predicting the Radius of the Sun as a Red Giant with SSM

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  14. J

    Will the Earth survive the Sun becoming a red giant?

    Is it likely that the Earth will survive or more likely that it will be engulfed?
  15. C

    Would Jupiter steal matter from our Sun when it reach red giant phase?

    It is closer to Sun than the distance between Sirius A and B. Yes I know that the Sun wound't expand so much to touch Jupiter, however it would be anyway blowing its mass away. Would Jupiter have strong enough gravitation to absorb significant amount of mass?
  16. R

    How Long Do Red Giant Stars Last?

    I have been unable to find any data or formula's on how long red giant type stars last other than a few million years!One would suppose that it is a function of its original mass and chemical composition. Any ideas...
  17. G

    Formation/Expansion of Red Giant

    Hello Physics Forums, complete astronomy noobie here. My question is about how a main sequence star turns into a red giant and starts expanding. Reading from here http://en.wikipedia.org/wiki/Red_giant "When the star exhausts the hydrogen fuel in its core, nuclear reactions in the core stop...
  18. D

    Will the red giant sun destroy the Earth?

    Will the Earth be destroyed?
  19. L

    Red Giant: The Death of a Star & Its Expansion

    When a star like the sun begins to die, what is the time frame over which the star develops into a red giant? How quickly will it expand?
  20. F

    The time of becoming a red giant

    How long would it take for a star, say approximately the mass of our Sun, to become a red giant? What I mean is the process of actually changing into a red giant. I know the star changes over its lifetime, but what I haven't found much information on is how fast the forming of a red giant...
  21. L

    What if the Earth could be moved away from the Sun when it becomes a red giant

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  22. O

    Why Do Stars Turn Red Giants as They Age?

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  23. marcus

    How long before the sun goes red giant?

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