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Questions tagged [red-giant]

Questions about red giants, large luminous low-mass stars in a late phase of stellar evolution.

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When a star enters a red giant phase, does the pressure in its core increase or decrease?

When a star becomes a red giant, does the pressure in its core increase or decrease? From one side, the only source of pressure in a star is gravity. A red giant is much larger than an ordinary star, ...
cuckoo's user avatar
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1 vote
0 answers
34 views

Hayashi Track vs Red Giant branch

Are the red Giant branch and the Hayashi track the same thing? After doing some research, I found some similarities between the two, such as both aree fully convective. However, the T Tauri phase does ...
Astrovis's user avatar
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7 votes
1 answer
146 views

Where will all atoms on the Earth end up when the Sun engulfs the earth?

I am curious about what will happen to all atoms on the Earth including all of our atoms after the Sun engulfs the Earth? Will they become the part of the Sun's white dwarf? Or most of them will be ...
tvd's user avatar
  • 71
2 votes
2 answers
241 views

How to predict the radius of a Red giant

I am working on a sci-fi that goes over such a large length of time that I will be having stars dying out, and this raises a question that I would need to find an answer to. How can one predict the ...
DanceroftheStars's user avatar
6 votes
1 answer
204 views

How did we figure out that Stars become red giants and when did we find out that they will?

I always hear that the Sun will be one but never when we found that out or how.
R-Obsessive's user avatar
0 votes
0 answers
48 views

What are the primary astrophysical implications of a proposed mass of about 11 M⊙ for the SN 2023ixf progenitor?

The abstract of the arXiv preprint SN 2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova (itself recently "discovered" in the observatory) ...
uhoh's user avatar
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1 vote
1 answer
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How do they see BOTH "anomalously cool with a significant mid-IR excess" rather than one or the other? (SN 2023ixf progenitor)

The abstract of the arXiv preprint SN 2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova (itself recently "discovered" in the observatory) ...
uhoh's user avatar
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2 votes
0 answers
38 views

Radius and surface temp of red giant Sun [duplicate]

There is wildly conflicting information going around about the predicted parameters of the Sun as a red giant. The estimates for the radius vary from 100 to even 256 solar radii (with the larger ...
Adam Kamil Gola's user avatar
7 votes
1 answer
352 views

Are red giants still primarily made of hydrogen? What is their exact composition?

How much lower is the ratio of hydrogen to helium in a red giant vs a 'normal' main sequence star like our Sun? Also, how low does the ratio get at the end of a red giant's life? (Just before it ...
Kurt Hikes's user avatar
  • 5,157
1 vote
1 answer
159 views

Which star has a higher effective temperature, a red dwarf or a red giant?

According to the Hertzsprung-Russell diagram, they would roughly have the same temperature, but I've read in bibliography that the surface temperature of the red giant is about 5000K and the one of ...
user9867's user avatar
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7 votes
2 answers
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Can a brown dwarf accrete enough mass from red giant to become a star?

Let's assume a brown dwarf is on orbit around a main sequence star. Than the star becomes a red giant. Let's assume the brown dwarf has "the right" orbit and can syphon matter from the red ...
Heopps's user avatar
  • 647
3 votes
0 answers
42 views

How can I calculate evolutionary timescales of low mass stars?

How can I calculate how long a star of a given mass will spend on an evolutionary branch before evolving off it? I'm thinking about the evolution of low mass stars from the subgiant branch to the red ...
Holly Bee's user avatar
4 votes
2 answers
520 views

How hot would the core of the Red Giant Sun be?

After the Sun becomes a red giant, it will heat up its core to 100 million kelvins, which initiates the Triple-Alpha fusion process, which heats up the star's core even further and cause it to undergo ...
Alastor's user avatar
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3 votes
0 answers
89 views

Are there any binary red supergiants?

I wonder if we ever have identified or observed a pair of binary stars (red supergiants). And I also wonder what would happen if they exploded, (theoretically) as we haven’t observed it. Also, would ...
schrodingerscat's user avatar
9 votes
2 answers
2k views

How bright will Alpha Centauri A be from Earth when it becomes a red giant?

As of right now, both stars from Alpha Centauri are in their main sequence stages, but eventually Alpha Centauri A is going to quickly expand in a matter of time, and I’m pretty sure its luminosity is ...
Prince Pugs's user avatar
6 votes
0 answers
156 views

Source of information on density profile of a red giant star?

Is there a good source of information of the expected density profile inside a red giant star? I have read that when a star such as the sun has converted much or most of the hydrogen in its core into ...
PAUL MILENKOVIC's user avatar
1 vote
2 answers
272 views

How much of the earth would remain intact if the sun expanded into a red giant encompassing its orbit?

It seems to me that part of the earth might survive being absorbed by a red giant. How long would it take the heat, plasma, magnetic field, etc. of the sun to eat away at the earth? How long could it ...
joseph.hainline's user avatar
2 votes
1 answer
173 views

Does a red giant star produce more stellar wind than a yellow star?

Do red giant stars produce more stellar wind than when they were ordinary yellow stars? If so, how big a difference are we talking about?
Constantthin's user avatar
4 votes
1 answer
581 views

How much mass is lost in the red giant phase of a star?

The red giant phase of stars are relatively fast. How will this impact a star's total mass? Are there significant mass losses taking place when this happens? If so, do we know how much? The sizes of ...
Constantthin's user avatar
0 votes
1 answer
178 views

Will the planets be pushed outwards when the sun goes red giant?

When the sun goes red giant will the planets be pushed outwards towards the periphery of the solar system? If so, will this happen simultaneously to all planets or could, for example, a planet like ...
Constantthin's user avatar
1 vote
1 answer
401 views

What exactly will happen when the Sun leaves the main sequence? I know it expands to a red giant twice, but what happens exactly? What's the timeline? [duplicate]

I've seen numerous claims surrounding this, with some claiming the expansion of the Sun from its end-main sequence radius to its peak red giant radius will take over 1 billion years, while others ...
Cryoraptor's user avatar
2 votes
0 answers
47 views

Dynamics of red giant hydrogen shell

From what I understood from this answer to How can a red giant grow so big? But this is not at all the way the shell fusing in a red giant self-regulates its fusion rate-- it cannot regulate its ...
Passer By's user avatar
  • 121
4 votes
1 answer
359 views

Where will the frost line be when the Sun becomes a red giant and what effect will it have on the solar system?

I understand the frost line is currently about 5.2 AU and earlier in the solar systems formation was 2.7 AU. But when the Sun becomes a red giant the frost line should move outward. I understand the ...
Brooks Nelson's user avatar
1 vote
0 answers
51 views

Why red giants have cooler surface than MS stars?

I know that with increasing age and depletion of hydrogen in the core the radiation inside a main sequence (MS) star increases pushing the envelope/surface of the star outwards. What I don't ...
NeStack's user avatar
  • 313
3 votes
0 answers
45 views

What is the theoretical maximum variability a pulsating red giant can have such that a habitable planet can stay habitable for long periods of time?

I was reading about red giants and came across this statement: Some research suggests that, during the evolution of a 1 M☉ star along the red-giant branch, it could harbor a habitable zone for ...
WarpPrime's user avatar
  • 6,673
4 votes
1 answer
116 views

Do low-mass red giants last longer than high-mass red giants?

It turns out that red giant stars are not defined by uniform mass. Some can be only one-third as massive as our sun, whereas others can be eight times as massive. So I'm calling the both sides "...
JohnWDailey's user avatar
1 vote
0 answers
52 views

Is a star with 2/3 solar masses and 9/10 solar radii still in the main sequence?

As far as I know, K-type and G-type stars (among others) grow in radius as they age, eventually leading to red giant phases. My question is, would a star that is about 0.66 solar masses and 0.94 solar ...
Xi-K's user avatar
  • 403
2 votes
1 answer
484 views

How does the stellar evolution for low and intermediate mass stars differ?

I'm trying to understand stellar evolutionary tracks for different masses. So far I have the general understanding from a cloud of gas and dust to a white dwarf, neutron star or black hole. What I don'...
JohnGoodWill's user avatar
7 votes
1 answer
173 views

Exactly how long does it take for the exposed core of a star to cool from its starting temperature (several billion K) to ~50,000 K?

OK, I didn't know how I should word this question. But the basic point is that most white dwarfs that we have classified fall in temperature ranges from ~50,000 K to 6000 K. However, at the end of a ...
WarpPrime's user avatar
  • 6,673
1 vote
1 answer
334 views

How large will our Sun get during the red giant phase (ie which planets will it engulf) before the helium flash?

I have read that our Sun will increase in size to a red giant. But after it goes through the helium flash it will contract somewhat. Then after that grow again to be even larger before finally ...
Brooks Nelson's user avatar
2 votes
2 answers
431 views

What would a red giant Sun look like from Proxima b?

As of now, Proxima b is the only confirmed planet (or dwarf planet if it didn't clear its orbit - sorry, couldn't resist) around Proxima Centauri, the nearest-known star to the Sun about 4.2 ly away. ...
John's user avatar
  • 75
11 votes
1 answer
2k views

If Sunlike stars become a red giant and eventually a white dwarf, what do red dwarfs become?

The Sun is said to become a red giant at the end of its life (before that it will become an orange subgiant first and then an orange giant or so) and after ejecting its outer layers it should become a ...
Giovanni's user avatar
  • 227
0 votes
0 answers
168 views

Could the Sun's planetary nebula be dangerous for the planets?

Since the Sun's mass isn't high enough it won't go supernova being a red giant but instead release a planetary nebula. So that seems to be kind of a substitute for a supernova. Would ejecting the ...
user30007's user avatar
  • 1,226
22 votes
2 answers
5k views

Do we know a star that is similar to the Sun when it would be a red giant?

In about 5 billion years the Sun is predicted to become a red giant and have more than 200 times its current size, reaching a radius of about 5 AU when largest. I wonder what spectral class the Sun ...
user30007's user avatar
  • 1,226
16 votes
3 answers
3k views

How would the sky look if Earth orbited a red giant at a safe distance?

Let's say that instead of the sun, we have a red giant, but are orbiting it at a safe distance, within the goldilocks zone. Would the sky actually look more red? Or would it be closer to white/...
Andrej Butić's user avatar
1 vote
0 answers
107 views

What if the Sun turned into a red giant tomorrow? [closed]

Let's say that, hypothetically, our sun uses up all of it's hydrogen tonight, and tomorrow morning is the first day of its red giant phase. How long would it take for the star to turn red? How long ...
Andrej Butić's user avatar
1 vote
0 answers
56 views

Relation between initial mass and evolutionary phases lifetimes

Consider the following image (Source: An Introduction to Modern Astrophysics): There seems to be a relation between the initial mass/mass at the beginning of the MS and the time spent during ...
Hrsht's user avatar
  • 333
2 votes
1 answer
222 views

How Long Will Earth's Year be When Our Sun Goes Red?

We live in a planet that orbits 93 million miles from a G-type main-sequence star, or "yellow dwarf". That is far enough for a revolution of 365 days. Such is the case of Kepler's Third Law of ...
JohnWDailey's user avatar
1 vote
1 answer
113 views

How Wide Would the Habitable Zone Be in a Singular Red Giant System?

Astrobiologists looking for signs of life outside Earth usually take excitement over planets orbiting red giant stars because a larger, brighter star usually means a farther-away but still wider ...
JohnWDailey's user avatar
2 votes
1 answer
107 views

In System KIC 9246715, How Far Does One Star Orbit the Other?

I was going to ask if it's physically possible for one red giant to orbit another, but fortunately, I have just found such a thing--a red giant binary system known only as KIC 9246715. In this ...
JohnWDailey's user avatar
1 vote
1 answer
919 views

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 ...
userLTK's user avatar
  • 24.1k
3 votes
1 answer
176 views

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 ...
sidharth chhabra's user avatar
3 votes
1 answer
3k views

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 ...
Johnny Dollard's user avatar
9 votes
2 answers
3k views

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 ...
klutt's user avatar
  • 191
18 votes
2 answers
2k views

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 ...
Ian Kemp's user avatar
  • 283
11 votes
2 answers
869 views

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 ...
velut luna's user avatar
16 votes
4 answers
2k views

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 ...
user541686's user avatar
4 votes
0 answers
272 views

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 ...
Jevon McPherson's user avatar
2 votes
0 answers
254 views

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 ...
Brooks Nelson's user avatar
4 votes
2 answers
385 views

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?...
shurrok's user avatar
  • 143