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Questions tagged [red-giant]

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Is there a theoretical minimum mass main sequence star that can become a red giant?

Wikipedia's Red Giant page says they range in mass from 0.3 to 0.8 solar masses. Which corresponds to an initial mass of a bit less than 1 solar mass, about 0.8 or so, if I was to estimate and a few ...
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What will be the temperature on Earth when Sun finishes its main sequence?

We know that presently Sun is 4.5 billion years into its main sequence. It has another 5 billion years before it enters the Red Giant phase. We also know that Sun's luminosity increases by 10% every ...
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1answer
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How long does it take a star to transition from main sequence to red giant?

I have read that it takes billions of years for stars of approximately the size of the Sun to get through the main sequence, after which it will enter the red giant phase. When that happens, how long ...
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How fast will the sun grow when it becomes a red giant?

We all know that our sun will become a red giant in a couple of billion years? But how fast will the process be when it starts? Would it be theoretically possible (disregarding the deadly effects of ...
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When a star reaches the red giant phase, why does it become more opaque?

Please refer to this answer from Quora: ... a star will become a red giant before it begins burning helium. In fact, it will bloat into a red giant while still burning hydrogen in a shell on the ...
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2answers
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Why is the track of the subgiant stage almost horizontal on the HR diagram?

It is stated that: After the main sequence, as fusion weakens or stops in the core, outward radiation weakens. The helium core contracts and heats up. Gravitational energy is converted to thermal ...
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4answers
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How can a red giant grow so big?

Supposedly when the sun becomes a red giant, it will grow big enough to swallow Earth. However, this requires the radius of the sun to expand by a factor of approximately 215×, meaning its volume ...
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How is Phosphorus made in in stars? [duplicate]

What elements are required to fuse into phosphorus in a star. Can someone give me a step by step process please e.g 4 hydrogen nuclei fuse into one helium nuclei and then 3 helium nuclei fuse ...
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Jupiter/Saturn's fate after Sun goes red giant and planetary nebula?

The solar wind contributes a very small amount of matter to the gas giants. As the sun approaches the red giant phase, the solar wind increases significantly. 10% of the sun's mass lost as solar ...
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2answers
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Origin of terms “white dwarfs” and “red giants”?

Can someone explain my why "white dwarfs" and "red giants" were so named? And maybe that's a silly question but why not in the opposite way? @EDIT Is this somehow co-related with Stefan–Boltzmann law?...
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2answers
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Could the Earth survive a red giant Sun?

So my question is that, is not a lie that we are flying away from the sun slowly, that is increasing by time because the sun loss mass, so when the scientist usually talk that we will get swallow by ...
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3answers
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When exactly does a sub giant become a red giant?

A simple, but interesting question I think. I understand that after the hydrogen exhaustion on the main sequence the post main sequence starts with the SGB where they burn hydrogen in a shell around ...
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1answer
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How can white dwarf form Oxygen ? (Temperature problem)

I’ve got a question about white dwarfs and oxygen. I read in a book that a temperature of 100 million degrees is required to fuse Helium in the core of a red giant. The Helium fuses into Carbon by ...
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2answers
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Why do post main sequence stars enter the red giants branch?

I am an early graduate student in astronomy and have hard time understanding why do post-MS stars move up the RGB. Here is what I understand about post main sequence evolution of stars. As their ...
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2answers
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What would be the apparent magnitude of Betelgeuse if it were as close to Earth as Sirius?

How large and bright would Betelgeuse appear if it were as close to Earth as Sirius, before and after it goes supernova?
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1answer
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Will the Sun rotate slower in red giant form?

When the Sun runs out of hydrogen to fuse it will grow bigger in size and my question is does it rotate more slowly, like a spinning ice skater extending their arms to reduce angular velocity? What ...
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Why do stars become red giants?

Disclaimer: I’m not a career astronomer. I don’t own a telescope. I have no professional credentials. But I do find this stuff fascinating, and I consume all the astronomy documentaries I can. ...
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1answer
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What happens to a star after it has become a red giant?

When our sun reaches the end of its lifetime , it will turn into a red giant. How long will it be a red giant, and what happens after a star has been a red giant? Does it turn into a planet after a ...