Red Giant: The Death of a Star & Its Expansion

[ladykrimson]

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?

 

[Drakkith]

The phases a star goes through are very very long on a Human time scale. It would take thousands to millions of years for a star to fully transition from one phase to another.

 

[Radrook]

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?

The following is in reference to our sun as illustrated in the Wiki chart.


1 1/2 billion years for warming to start

5 1/2 half billion years to reach its red giant stage

1 billion years in red giant stage

1 billion years in the planetary nebula stage

3 billion years in the white dwarf stage

http://en.wikipedia.org/wiki/Stellar_evolution



Seven billion years to reach its red giant stage.

 

[ladykrimson]

So as a star goes through it's red giant stage, is it losing mass or gaining mass?

 

[Drakkith]

So as a star goes through it's red giant stage, is it losing mass or gaining mass?

Other than a star that is pulling in matter from something near it, all stars lose mass as they age due to solar wind, emitting light, ETC.

 

[Radrook]

So as a star goes through it's red giant stage, is it losing mass or gaining mass?

As the previous poster said all stars lose mass as they fuse one element into another. Our sun is fusing hydrogen into Helium and is presently losing approximetly 4 million metric tons per second in the process.

 

[qraal]

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?

The Sun will go off the Main Sequence in about 5.5 billion years. It will gradually rise in brightness and grow cooler during the Redwards Traverse. When The Sun is about 12.2 billion years old the slow rise picks up speed and it rapidly balloons to its maximum Red Giant size in about 30 million years. As it does so the solar wind intensifies and the Sun throws off about 25% of its mass in the last few million years.

The Red Giant stage ends with the Helium flash - a runaway helium fusion explosion in the Sun's core. Most of the energy released goes into expanding the core into a stable helium-fusion burning stage, the Horizontal Branch or Helium Main Sequence, which lasts just 100 million years, unlike the 10 billion of the Hydrogen Main Sequence. When the Helium Main Sequence ends the Sun swells rapidly into a new Red Giant stage, the Asymptotic Giant Branch, which sees multiple expansions and contractions of the Sun, throwing off another 20% of the Sun's mass. What remains is a slowly cooling carbon/oxygen white dwarf that, contrary to an earlier poster, lasts as long as matter survives. A white dwarf takes many billions of years to cool below red-heat (about 840 K), after which it can be called a "black dwarf", but the Universe isn't old enough for any to have grown so cold yet.

 

[Radrook]

There is definitely a limit to the white dwarf stage and its existence isn't limitless as the previous poster pointed out. As he himslf pointed out, the white dwarf eventually turns into a black dwarf, a burnt out cinder giving off no light at all. So it definitely isn't eternal as the previous poster's self-contradicttion says. Sorry but you can't have it both ways.


BTW
Perhaps the key to unravelling this mysterious eternal white dwarf statement lies in the "as long as matter survives" comment? But then again that comment is followed by an admission that it turns into a black dwarf? Which would require that the black dwarf and the rest of the universe be composed of something other than matter in order for the statement to make sense.

 

[Drakkith]

What remains is a slowly cooling carbon/oxygen white dwarf that, contrary to an earlier poster, lasts as long as matter survives.

My mistake, I meant a star that is "active", or whatever you want to call it, will lose mass due to solar wind and such. A white dwarf, not being active anymore, will not lose mass except by the emission of radiation until it cools completely, at which point it will not anymore.

 

[Radrook]

My mistake, I meant a star that is "active", or whatever you want to call it, will lose mass due to solar wind and such. A white dwarf, not being active anymore, will not lose mass except by the emission of radiation until it cools completely, at which point it will not anymore.

Thanx. You had me going there for a while. LOL

BTW
You have two different names on this forum?

 

[Drakkith]

Thanx. You had me going there for a while. LOL

BTW
You have two different names on this forum?

Lol no, I was responding to Qraal. You replied about 30 seconds before i did.

 

[qraal]

Radrook, a white dwarf star doesn't end if matter is eternal, but will eventually decay if protons are ultimately unstable.

 

[Radrook]

Radrook, a white dwarf star doesn't end if matter is eternal, but will eventually decay if protons are ultimately unstable.

Of course! It also depends on if the big rip happens based on the discovery of this mysterious dark energy which accelerates our universal expansion doesn't it? But the question wasn't about the ultimate fate of matter as far as I can tell. It is about the time it takes for our sun to reach the Red GIANT STAGE, the duration of that stage. I based my response on the chart provided at Wiki. Do you see any other way to understand that chart? It doesn't include the cinder burnt out stage of the star but just the white dwarf stage.

Also, a black cinder isn't a white dwarf. So a white dwarf is NOT eternal. It ceases to exist when it stops radiating. THe term "white" is in reference to the light it gives off as it continues to die or cool down. So what you really mean is that the remains of the white dwarf might be eternal if matter is eternal and not that the white dwarf is eternal. We have to get our terminology right in order to avoid confusion via misunderstandings.


.

 

[Ken G]

I based my response on the chart provided at Wiki. Do you see any other way to understand that chart?

I believe the answer there is that the Wiki chart is not intended to have an endpoint-- the "white dwarf" phase just continues for quite a while off the right edge of the chart. As you have already discussed with qraal, just exactly when a white dwarf should no longer be termed a white dwarf is a largely semantic issue, but it will take a lot longer than 3 billion years to encounter that semantic boondoggle, which is I think the main point qraal was making.

 

[qraal]

I believe the answer there is that the Wiki chart is not intended to have an endpoint-- the "white dwarf" phase just continues for quite a while off the right edge of the chart. As you have already discussed with qraal, just exactly when a white dwarf should no longer be termed a white dwarf is a largely semantic issue, but it will take a lot longer than 3 billion years to encounter that semantic boondoggle, which is I think the main point qraal was making.

Thanks Ken G,
My point exactly. As for the end of matter I was thinking of the very distant future prospect of proton decay, apparently via something other than GUTs since it hasn't been observed in any search yet conducted. Protons, being composite objects, should collapse into black holes over sufficiently long time spans - via the constituent partons overlapping their collective event horizon. A low probability event, but inevitable given enough time, unless we're totally wrong about particle physics.

 

[Radrook]

I believe the answer there is that the Wiki chart is not intended to have an endpoint-- the "white dwarf" phase just continues for quite a while off the right edge of the chart. As you have already discussed with qraal, just exactly when a white dwarf should no longer be termed a white dwarf is a largely semantic issue, but it will take a lot longer than 3 billion years to encounter that semantic boondoggle, which is I think the main point qraal was making.

If English is spoken clearly it is understood clearly. If a person says that a white dwarf never ends then that's very simply understood as stated. The duration time indicated by the chart is 3 billion years. Blame the chart for misleading. I simply stated what the chart indicates. If indeed the durartion is longer or unknown then the chart should have indicated it with an arrow indicating continuation at the least.

BTW
I just found the same chart on another website with a caption telling the reader that the duration of the white dwarf stage isn't known. If that caption had been responsibly included in the wiki chart I would not have made that statement.

 

[qraal]

If English is spoken clearly it is understood clearly. If a person says that a white dwarf never ends then that's very simply understood as stated. The duration time indicated by the chart is 3 billion years. Blame the chart for misleading. I simply stated what the chart indicates. If indeed the durartion is longer or unknown then the chart should have indicated it with an arrow indicating continuation at the least.

BTW
I just found the same chart on another website with a caption telling the reader that the duration of the white dwarf stage isn't known. If that caption had been responsibly included in the wiki chart I would not have made that statement.

I admit I didn't make myself very clear, but eye-balling figures off a Wikipedia article's chart isn't a very accurate data source to answer a questioner, surely?

 

[Radrook]

I admit I didn't make myself very clear, but eye-balling figures off a Wikipedia article's chart isn't a very accurate data source to answer a questioner, surely?

I find the Wiki info to be pretty reliable. In any case, I'm merely following what I see some
others doing here. Quoting wiki articles and directing questioners to Wiki as an acceptable information source. As for accuracy, all Wiki articles include sources. So once a reader is guided there all he needs to do is verify via those links. I usually do that myself but had no time due to serious personal problems. But since WIKI isn't acceptable, according to you, then I will never use it as a reference again. Thanx for the advice!

 

[ladykrimson]

I find the Wiki info to be pretty reliable. In any case, I'm merely following what I see some
others doing here. Quoting wiki articles and directing questioners to Wiki as an acceptable information source. As for accuracy, all Wiki articles include sources. So once a reader is guided there all he needs to do is verify via those links. I usually do that myself but had no time due to serious personal problems. But since WIKI isn't acceptable, according to you, then I will never use it as a reference again. Thanx for the advice!

I'm sure you can use Wiki as a reference, as long as you confirm the information with another source. The only reason Wiki is unreliable is because anyone can edit the information. I have checked some of the references that Wiki lists and found dead links. If you do use it, just confirm your information.

 

[ladykrimson]

OK, then if the sun will begin to lose mass once it enters the red giant phase, doesn't it stand to reason that the gravitational pull on Earth will decrease?

 

[Ken G]

Yes, and that means the radius of Earth's orbit will increase. This is the reason that the Earth will never be inside the Sun, even if the Sun's envelope eventually expands past 1 AU.

 

[qraal]

I find the Wiki info to be pretty reliable. In any case, I'm merely following what I see some
others doing here. Quoting wiki articles and directing questioners to Wiki as an acceptable information source. As for accuracy, all Wiki articles include sources. So once a reader is guided there all he needs to do is verify via those links. I usually do that myself but had no time due to serious personal problems.But since WIKI isn't acceptable, according to you, then I will never use it as a reference again. Thanx for the advice!

I salute your dedication in adversity. Use whatever source you wish - ignore my nit-picking, sorry. And thanks for the critique. Next time I'll try not to be so vague.

 

[Chronos]

A white dwarf that is not accreting from a companion star can take trillions of years to cool sufficient to be considered a black dwarf. None are believed to exist in the universe. I agree Wiki is not sufficiently reliable to be quoted as an authoritative source. I prefer arxiv, but, even arxiv is not bullet proof. I find about half the papers on arvix to include questionable assumptions. OK, I'm not very trusting.