What is Red giant: Definition and 20 Discussions

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. Vanadium 50

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

    The Guardian claims Betelgeuse is the closest red giant to Earth. Not even close. Aldebaran Arcturus Mira Delta Andromedae The abominably named Gacrux Capella, which despite the color is a red giant Possibly Antares (distances are similar) And, what is likely the correct answer, Pollux. Think...
  2. Philosophaie

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

    What happens first Sun Red Giant or Andromeda collision?
  3. S

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

    I'm not sure this a strictly Astronomy question; perhaps it should go in Aerospace Engineering. I have always thought that Dyson's work was more of an Astronomy topic, although admittedly, from the POV of observing some other system's sphere. In any case, I was thinking about future...
  4. O

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

    Hey. Medium sized stars will turn into red giants. What about big sized stars? As far as I know they will turn into red SUPERgiants. But, will they pass through a red giant phase before it happens? In conclusion, will a big star turn firstly into a red giant and secondly into a red supergiant...
  5. T

    B Why will Betelgeuse go supernova?

    Betelgeuse is a red supergiant, yet I have heard that Betelgeuse will go supernova in the next million years. How is this possible? Wouldn't Betelgeuse be too cool to go supernova? Normally red supergiants produce white dwarfs and planetary nebulae.
  6. T

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

    When a high mass star starts to fuse heavier elements, the core heats up the outer layers enough to for them to begin fusion of their own. My question is: because the star hasn't gained any mass, but it has increased in temperature a lot, why doesn't the star expand and cool like a red giant...
  7. Madi Araly

    Increase in Radius when a Star becomes a Red Giant

    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...
  8. 2

    Difference between a red giant and red supergiant?

    These two types of stars clearly must have different properties because they form distinct groups on a Hertzsprung-Russell diagram. I have also read that red supergiants can form elements up to around carbon by nuclear fusion, whereas red supergiants can form up to iron, however there doesn't...
  9. JohnPrior3

    Death of Sun: Habitable Zone & Timeline

    So I am working on making a simulation that shows the habitable zone of our solar system from now until our sun reaches the end of it's red giant phase. The sun will die when it is 10 billion years old and will reach the end of the red giant stage at 5 billion years. I know the habitable zone...
  10. 1

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

    How can SSM be utilized to predict the radius of the Sun when it becomes a red giant?
  11. 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?
  12. 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?
  13. 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...
  14. 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...
  15. D

    Will the red giant sun destroy the Earth?

    Will the Earth be destroyed?
  16. 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?
  17. 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...
  18. L

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

    If we could move the Earth, how far away from the Sun would it need to be to maintain a temperature similar to what we have now when it becomes a red giant? How large would the Sun apear in the sky? Would the sky still be blue? Would everything have a red tint to it? I was...
  19. O

    Why do stars become red giants?

    A star which radiates as a blackbody has an increasing temperature almost it's entire life. If it begins as a huge, hot blue-white star, why is it that it's called a red giant when the hydrogen runs out? If the temperature is higher, it should be radiating mostly in the ultraviolet region of the...
  20. marcus

    How long before the sun goes red giant?

    A french poster (ant284) just came to HomeworkHelp with a question about the lifetime of the sun. Some say the sun will go red giant when it has consumed 12 percent of its hydrogen. The sun is now 75 percent hydrogen. We know its mass so we can tell how much hydrogen is supposed to be...