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Tags astronomy , Betelgeuse , supernovas

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Old 25th January 2020, 09:34 PM   #1
cullennz
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Apparently Betelgeuse is about to go Supernova

https://www.forbes.com/sites/startsw.../#54871a2b43a2


Pretty freaky
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Old 25th January 2020, 10:25 PM   #2
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Unable to read that because it wants to disable ad blocking. Are they saying Betelgeuse nova'ed six hundred plus years ago so we'll see it soon, or are they saying it's about to nova now and it'll be visible here in six hundred plus years?

I'm sure it'll be pretty but possibly not worth waiting around for.
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Old 25th January 2020, 11:44 PM   #3
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Originally Posted by TragicMonkey View Post
Unable to read that because it wants to disable ad blocking. Are they saying Betelgeuse nova'ed six hundred plus years ago so we'll see it soon, or are they saying it's about to nova now and it'll be visible here in six hundred plus years?

I'm sure it'll be pretty but possibly not worth waiting around for.
Fair call quite interesting though
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Old 26th January 2020, 12:46 AM   #4
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Actually, it probably isn't. According to some recent models, it as a whole may be younger than we previously thought, being actually the merger of two smaller stars. So it may have a few million more years left.
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Old 26th January 2020, 04:11 AM   #5
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I give you this thread on the same subject.

Which is first: Betelgeuse Supernova or Second Coming
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Old 26th January 2020, 04:18 AM   #6
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I guess if some neutrino detectors detect heaps of neutrinos then heaps of telescopes will turn their attention to this star no matter what the cause of the neutrinos is.
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Old 26th January 2020, 05:01 PM   #7
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Rats.

I was hoping this was going to be a thread about Beetlejuice Goes Hawaiian...

https://en.wikipedia.org/wiki/Beetle...ossible_sequel
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Old 26th January 2020, 05:08 PM   #8
HansMustermann
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Originally Posted by TragicMonkey View Post
Unable to read that because it wants to disable ad blocking. Are they saying Betelgeuse nova'ed six hundred plus years ago so we'll see it soon, or are they saying it's about to nova now and it'll be visible here in six hundred plus years?

I'm sure it'll be pretty but possibly not worth waiting around for.
IF Betelgeuse actually were "about to go supernova", it would really mean it happened already and we're about to observe it.
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Old 26th January 2020, 05:21 PM   #9
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Just my luck. It's winter in The Great Northwet and "sky" is somewhat of an abstract concept. Like "sun".
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Old 26th January 2020, 11:01 PM   #10
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One thing about red giants is that although their radius and volume is much bigger, the actual mass is not so much.

So, Wikipedia gives the mass of Betelgeuse as 11.6+5.0/−3.9 M☉ but its radius is 900 times bigger than our sun and its volume is 700 million times larger, so it's much less dense on average. I wonder if the mass is relatively uniformly distributed or if it's much denser at the center than near its surface?
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Old 27th January 2020, 12:05 AM   #11
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Originally Posted by Puppycow View Post
One thing about red giants is that although their radius and volume is much bigger, the actual mass is not so much.

So, Wikipedia gives the mass of Betelgeuse as 11.6+5.0/−3.9 M☉ but its radius is 900 times bigger than our sun and its volume is 700 million times larger, so it's much less dense on average. I wonder if the mass is relatively uniformly distributed or if it's much denser at the center than near its surface?
On the surface there is nothing compressing the material. However deeper down there is all the mass above that to compress the material. It is also far more likely to be made of the heavier elements. Hence the density difference increases the older and the heavier the star is.
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Old 27th January 2020, 04:35 AM   #12
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If mass were evenly distributed, you wouldn't get fusion in the core. You actually need the pressure and temperature there for fusion.
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Old 27th January 2020, 04:46 AM   #13
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That said, on the topic of more mass but less density, it helps to remember that all the photons coming from the centre exert radiation pressure on the plasma above. Photons don't have mass, but have momentum anyway, so when a photon coming from below is absorbed by a charged particle above, conservation of momentum still applies, so that particle is shoved upwards. When it's re-emitted, it's in a random direction, which means half the time it's backwards, so the particle is nudged even more upwards. (And the layers below that absorb it get pushed a bit downwards.)

So basically the star is so big because it produces a lot of energy, i.e., a lot of photons, which keep pushing its outer layers outwards. While gravity is doing its best to keep them back. Basically it's like when you throw a ball upwards. If you throw it with more energy, it goes higher. Except here the ball is a particle in the plasma that makes up the star.

When fusion stops, there's nothing more pushing upwards, and the star starts to collapse fast. If the resulting extra pressure and heat (as potential energy gets converted into kinetic energy) are enough to start fusing the next set of elements, the star restarts basically. If it already went as high as it can go (either not big enough, or it already fused up to iron and nickel), then not. And if it's big enough, its outer layers can go kablooie.
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Old 27th January 2020, 05:11 AM   #14
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Thanks for that explanation. Putting the "E" in the JREF forum.
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Old 27th January 2020, 06:10 AM   #15
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When you consider the huge volume - out past the orbit of Mars in our solar system, and the relatively low mass - only about twelve times the mass of our Sun, then the outer parts of Betelgeuse are an extremely good vacuum.
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Old 27th January 2020, 09:18 AM   #16
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In terms of density? Absolutely. In terms of pressure? Eh, maybe not so much.
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Old 27th January 2020, 09:29 AM   #17
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The article in the OP doesn't seem to be suggesting an immanent supernova. From the link in the OP:
Quote:
There's no scientific reason to believe that Betelgeuse is in any more danger of going supernova today than at any random day over the next ~100,000 years or so, but many of us — including a great many professional and amateur astronomers — are hoping to witness the first naked-eye supernova in our galaxy since 1604.
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Old 27th January 2020, 12:43 PM   #18
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Originally Posted by lomiller View Post
The article in the OP doesn't seem to be suggesting an immanent supernova. From the link in the OP:
Please remember in astronomy 100,000 years is soon. If it will explode in the next 100,000 years then the probability of it exploding in the next 20 years is one in 5,000. People have bought tatts tickets with worse odds than that.
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Old 27th January 2020, 12:59 PM   #19
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Originally Posted by ceptimus View Post
When you consider the huge volume - out past the orbit of Mars in our solar system, and the relatively low mass - only about twelve times the mass of our Sun, then the outer parts of Betelgeuse are an extremely good vacuum.

On average Betelgeuse is five decimal orders of magnitude less dense than Earth's atmosphere. But pretty much the out parts of any atmosphere are going to be near vacuum.

Originally Posted by HansMustermann View Post
In terms of density? Absolutely. In terms of pressure? Eh, maybe not so much.

What distinction are you making here? Density and pressure would be related.
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Old 27th January 2020, 02:10 PM   #20
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Originally Posted by RecoveringYuppy View Post
What distinction are you making here? Density and pressure would be related.
Sure, they're related to temperature as well. You can increase pressure by increasing temperature without increasing density.
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Old 27th January 2020, 02:17 PM   #21
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Originally Posted by phunk View Post
Sure, they're related to temperature as well. You can increase pressure by increasing temperature without increasing density.
But Betelgeuse isn't sealed in a bottle.
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Old 27th January 2020, 02:53 PM   #22
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Originally Posted by RecoveringYuppy View Post
What distinction are you making here? Density and pressure would be related.
Related, yes. Identical, no.

Think this: why does a hot air ballon rise? The pressure inside is identical to the pressure outside, since it has an open bottom. But a lot less density is needed to achieve the same pressure, if the temperature goes up a bit.

Really, there is no requirement for anything to be sealed in a bottle. The ideal gas law is the same: PV = nRT. Where P is pressure, V is volume, n is number of moles of gas, R is the ideal gas constant, and T is temperature. And if you move V to the right side, n/V is proportional to density for the same gas, and basically what you get is that the pressure is proportional to density (for the same gas) times the temperature.

That applies just as well to the air outside, or near your heater, or whatever. It's what causes convection for example. If pressure is constant (because it's atmospheric pressure), when temperature rises, density must fall, so you get less dense air, and it rises courtesy of Archimedes.
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Old 27th January 2020, 02:59 PM   #23
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Or to apply that to Betlegeuse, think this: what is the density of hydrogen on Earth at ground pressure and temperature. About 0.08 kg/m3. Well, not a whole lot. Now think that the surface of Betlegeuse is about 3500k, so about 12 times room temperature. To have the same 1 atmosphere pressure without violating that gas law, it only needs to be 12 times less dense. About 0.007 kg/m3 would do the trick. It's not a lot of density, but it gets you 1 atmosphere pressure.
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Old 27th January 2020, 03:05 PM   #24
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Originally Posted by HansMustermann View Post
Really, there is no requirement for anything to be sealed in a bottle.
The relation phunk cited requires constant volume.

Originally Posted by HansMustermann View Post
The ideal gas law is the same: PV = nRT. Where P is pressure, V is volume, n is number of moles of gas, R is the ideal gas constant, and T is temperature. And if you move V to the right side, n/V is proportional to density for the same gas, and basically what you get is that the pressure is proportional to density (for the same gas) times the temperature (and across longer distances the only other factor is the r-squared fall off).

That applies just as well to the air outside, or near your heater, or whatever. It's what causes convection for example. If pressure is constant (because it's atmospheric pressure), when temperature rises, density must fall, so you get less dense air, and it rises courtesy of Archimedes.

That's all nice but doesn't help explain what you said about the outer edges of Betelgeuse's atmosphere. Both density and pressure are going to be low there. Pressure in the outer edges of Betelgeuse's atmosphere is simply a function of cumulative density above whatever point you are talking about. That will hold across any distance short enough to avoid the r-squared falloff of the gravitational field.

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Old 27th January 2020, 04:29 PM   #25
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Originally Posted by HansMustermann View Post
Or to apply that to Betlegeuse, think this: what is the density of hydrogen on Earth at ground pressure and temperature. About 0.08 kg/m3. Well, not a whole lot. Now think that the surface of Betlegeuse is about 3500k, so about 12 times room temperature. To have the same 1 atmosphere pressure without violating that gas law, it only needs to be 12 times less dense. About 0.007 kg/m3 would do the trick. It's not a lot of density, but it gets you 1 atmosphere pressure.

You've only accounted for one similarity/difference to Betelgeuse so this situation you describe doesn't necessarily describe Betelgeuse at all. And I still don't see how this relates to what you said earlier.

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Old 27th January 2020, 04:58 PM   #26
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Originally Posted by RecoveringYuppy View Post
On average Betelgeuse is five decimal orders of magnitude less dense than Earth's atmosphere. But pretty much the out parts of any atmosphere are going to be near vacuum.
Yes - and obviously the core of the star is extremely dense - but with huge giants like Betelgeuse, even when you're about half way between the centre and the outer 'surface' that we measure the star's diameter at - so many tens of millions of miles deep inside the star - you're still in a pretty good vacuum - a very hot vacuum admittedly, but on Earth we would class both the pressure and density there as 'near vacuum'.

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Old 27th January 2020, 05:20 PM   #27
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Originally Posted by ceptimus View Post
Yes - and obviously the core of the star is extremely dense - but with huge giants like Betelgeuse, even when you're about half way between the centre and the outer 'surface' that we measure the star's diameter at - so many tens of millions of miles deep inside the star - you're still in a pretty good vacuum - a very hot vacuum admittedly, but on Earth we would class both the pressure and density there as 'near vacuum'.
OK. So your point is that even quite a bit of the inner portions of Betelgeuse are near vacuum. Obviously I agree that Betelgeuse is tenuous since I just cited the average density.
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Old 27th January 2020, 05:39 PM   #28
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Originally Posted by HansMustermann View Post
IF Betelgeuse actually were "about to go supernova", it would really mean it happened already and we're about to observe it.
Over 600 years ago..
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Old 27th January 2020, 05:42 PM   #29
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@RecoveringYuppy
ceptimus said "the outer parts of Betelgeuse", not the atmosphere of it.

We're talking about a start that's about 700 million kilometres in radius. So where do you draw the line that the "outer parts" begins? I mean, if you go 100 million kilometres inside, it's still pretty outer, right? (Incidentally it puts you at 4 times the orbital radius of Earth, or 2 times the orbital radius of the asteroid belt. Seems kinda outer to me.)

Well, the pressure there (including radiation pressure) has to support the weight of the 100 million km above it. At at a gravity 12 times or so higher than the Sun's. Low density as that may be, it's still adding up. I wouldn't necessarily call that pressure a very good vacuum, is all I'm saying
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Old 27th January 2020, 05:43 PM   #30
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Originally Posted by cullennz View Post
It is more a wish on a star from astronomers . This Is What We'll See When Betelgeuse Really Does Go Supernova
Quote:
There's no scientific reason to believe that Betelgeuse is in any more danger of going supernova today than at any random day over the next ~100,000 years or so, but many of us ó including a great many professional and amateur astronomers ó are hoping to witness the first naked-eye supernova in our galaxy since 1604.
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Old 27th January 2020, 07:28 PM   #31
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Originally Posted by HansMustermann View Post
@RecoveringYuppy
ceptimus said "the outer parts of Betelgeuse", not the atmosphere of it.
Yes, I understand that based on his last message. I think his point would have been clearer if he'd said something like "most of Betelgeuse is a good vacuum".


What is "gravity 12 times or so higher than the Sun's" meant to refer to?

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Old 27th January 2020, 10:00 PM   #32
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Science, I need the science... (Thanks Hans)

Universe Today - 5 days ago: Betelgeuse is Continuing to Dim! Itís Down to 1.506 Magnitude
Quote:
Betelgeuse keeps getting dimmer and everyone is wondering what exactly that means. The star will go supernova at the end of its life, but thatís not projected to happen for tens of thousands of years or so. So whatís causing the dimming? ...

According to Guinan and Wasatonicís post on Astronomerís Telegram, Betelgeuseís temperature has dropped by 100 Kelvin since September 2019, and its luminosity has dropped by nearly 25% in the same time frame. According to all of those measurements, the starís radius has grown by about 9%. This swelling is expected as Betelgeuse ages. ...

Like all stars, Betelgeuse generates heat in its core through fusion. The heat is transferred to its surface via convection. The currents that carry the heat are called convection cells, which can be seen on the surface as dark patches. As the star rotates, these cells rotate in and out of view, which contributes to Betelgeuseís observed variability. Convection cells can be massive, even more so on the surface of a huge star like Betelgeuse. In 2013 scientists reported evidence of convection cells on the Sun that lasted for months. It wasnít conclusive, but could something like that be happening on Betelgeuse, contributing to the dimming?

This dimming episode may not be the star itself, but rather a cloud of gas and dust obscuring the light. As time goes on, and Betelgeuse burns more of its fuel, it loses mass. As it loses mass, its gravitational hold on its outer edges is weakened, and clouds of gas escape the star into the surrounding regions. This could cause the current dimming episode.
I'm going to guess some 'science' reporter skimmed the story.

This looks like the paragraph that might have been misunderstood:
Quote:
Whatever the cause, we know what the eventual end for Betelgeuse looks like: a supernova explosion. Whether this dimming is directly related to the approaching cataclysmic death of this unstable star is unknown at this point. As Guinan and Wasatonic say on Astronomerís Telegram, ďThe unusual behavior of Betelgeuse should be closely watched.Ē
And this one:
Quote:
When exactly all this will happen, nobody knows. And though this recent dimming likely isnít directly connected to Betelgeuseís eventual supernova explosion, astronomers donít know that for sure either.
Said reporter should have paid more attention to the rest of the article. Or maybe there was purpose to their madness.
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Old 27th January 2020, 10:21 PM   #33
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I guess there's a small, but highly unlikely possibility that the recent dimming indicates the start of a collapse that would result in a supernova at the end of the star's life.

Far more likely, however, is that it's just part of its natural variability. It regularly dims and brightens over a cycle of about 400 days, and there seems to also be a longer cycle of 2100 days.

https://en.wikipedia.org/wiki/Betelgeuse#Variability

Quote:
Betelgeuse typically shows only small brightness changes near to magnitude +0.5, although at its extremes it can become as bright as magnitude 0.0 or as faint as magnitude +1.3. Betelgeuse is listed in the General Catalogue of Variable Stars with a possible period of 2,335 days.[6] More detailed analyses have shown a main period near 400 days and a longer secondary period around 2,100 days.[73][82] The lowest reliably-recorded V-band magnitude of +1.294 was reported in late December 2019.[67][54]
I guess wikipedia might need some updating. 1.506 magnitude would be dimmer than it's ever been recorded before, if true.
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Old 27th January 2020, 10:24 PM   #34
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Here's the original source for that story, btw:

http://www.astronomerstelegram.org/?read=13410
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Old 28th January 2020, 01:21 AM   #35
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Originally Posted by RecoveringYuppy View Post
What is "gravity 12 times or so higher than the Sun's" meant to refer to?
Unless my memory fails me (which it might,) the average estimated mass of Betlegeuse is about 12 solar masses or so (albeit with a VERY high margin of error). So gravity being GM/r2, at the same distance the matter will be about 12 times "heavier" than in our Sun's gravity well. So, yeah, those outer parts will press a little bit harder on the parts below them.
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Old 28th January 2020, 01:31 AM   #36
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That said, about Betlegeuse exploding, there are two flies in that soup.

1. It seems to be spinning insanely fast, by star standards.

2. It has an unusually high metallicity (basically everything above helium is "metal" when talking about a star) at its surface.

A recent theory says that this is consistent with it being what happens when you have a binary system that ends up merging into one star. All that orbital momentum transforms into spin of the star, because conservation of momentum still applies. The resulting star is also given a good stir, so you start seeing a lot more of the stuff from the core in the outer layers.

Why that's important is because then our previous models about it are basically awfully wrong. The star probably used up a lot less of its fuel than we previously thought. Instead of looking at it going kablooie anywhere in the next 10,000 years, we may well be looking at it having a good couple million years left.
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Old 28th January 2020, 01:51 AM   #37
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Originally Posted by HansMustermann View Post
Unless my memory fails me (which it might,) the average estimated mass of Betlegeuse is about 12 solar masses or so (albeit with a VERY high margin of error). So gravity being GM/r2, at the same distance the matter will be about 12 times "heavier" than in our Sun's gravity well. So, yeah, those outer parts will press a little bit harder on the parts below them.
Right, but at a distance that is effectively farther away from the center of mass than Mars is to the sun.

Obviously you cannot stand on the "surface" of Betelgeuse because it doesn't really have one, at least not a solid one until you get well inside (and it's too hot of course). But at what we call the "surface" or even some distance inside the "surface", you are very far away from the center of mass and the density in this region would be quite sparse.

I was also thinking that if Betelgeuse before it swole up into a supergiant, at an earlier stage of life, had a system of planets, then probably at least several inner ones got swallowed up. But it might take some time for them to fall to the middle, since the plasma out there is pretty thin.
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Old 28th January 2020, 02:18 AM   #38
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I was talking about at the same distance, when talking about the pressure exerted by those "outer parts". Basically it's not just that it's a lot of matter exerting pressure when you go like 100 million km inside Betelgeuse, it's also in a deeper gravity well. Basically pressure being a matter of force/surface, the force is the weight of those layers, which means GMm/r2. You need to take the mass of the star into account too. Is all I'm saying.
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Old 28th January 2020, 07:08 AM   #39
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Originally Posted by HansMustermann View Post
Unless my memory fails me (which it might,) the average estimated mass of Betlegeuse is about 12 solar masses or so (albeit with a VERY high margin of error). So gravity being GM/r2, at the same distance the matter will be about 12 times "heavier" than in our Sun's gravity well. So, yeah, those outer parts will press a little bit harder on the parts below them.
But we're talking about stuff at large r, so not the same distance. Not terribly close to the same, even.
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Old 28th January 2020, 07:53 AM   #40
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Originally Posted by HansMustermann View Post
I was talking about at the same distance, when talking about the pressure exerted by those "outer parts".

This doesn't make any sense to me and seems to be at the root of the confusion here. What can "same distance" for the "outer parts" of Betelgeuse possibly mean? The entire Sun occupies less than one tenth of one percent of the volume of Betelgeuse.
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