_>
Yeah, the mass (which is hydrogen and helium) gets burned up to create all the heat and light. That's where it all goes. The entire star is just a great big flaming ball of fuel being constantly burned up.
The mass disappears because of the same reason that coal disappears when you burn it; it's getting converted into energy. There's more detail about the expansion process here: http://en.wikipedia.org/wiki/Red_giant | |
One thing I'm curious about, if matter can convert to energy, can the reverse apply? Can energy create matter?
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A highly combustible asteroid would do crap all. It would still have a good deal more kinetic then chemical energy, and most of the explosive force wouldn't go into the Earth, anyway.
I would consider 'destroyed' to be 'fragmented, and in such a way that it won't collect back into a planet again'. It's surprisingly difficult to do. Stars expand as they get to the end of the stellar life-cycle, because they start fusing helium, which produces more outwards pressure - they can grow by an order of magnitude or more. The surface gets colder, but only to about 8000 K, which is still 'damned warm' on the absolute chart. | |
Nope. The mass would still have barely changed, why would it change Earth's orbit? And decreasing the sun's mass would likely push the Earth into an orbit further out, rather then further in.
Of course, it might expand to the point where Earth is inside the Roche limit of the sun, which would destroy it. But I think current estimates put the Earth's orbit outside the eventual radius of red-giant sun - I'm not positive, though. | |
Actually, stellar expansion is caused by the shift to fusing helium - it produces more thermal energy then the proton-proton cycle, which produces a larger outwars force to counter gravity.
And the Earth would be toast before hitting the 'atmosphere' of the Sun - it would have to pass through the Roche limit first, and get torn to shreds by tidal forces. | |
Energy is released because the mass of a helium nucleus, plus the binding energy of a helium nucleus, is less then the mass of a hydrogen nucleus, plus the binding energy of a hydrogen nucleus, times two. The two neutrons can sort of 'share' some of their energy, so it a helium nucleus takes less energy to build then two hydrogen nuclei have. So getting a helium from two hydrogens would produce a net deficit of energy, which is illegal - the extra energy is radiated out as electromagnetic energy.
That's a slightly simplified explanation, but it's got the basics there. | |
<font color="blue">CaptFalcon33035 wrote:
Um.. a giant red ball? From what I know, if a star were to expand (as the larger ones are closer to red and the smaller ones closer to white), it would also get cooler than it currently is...</font> while that is the theory, it cools relative to it's previos state. this is still more than hot enough to fry the planet into a charcoal brickette during it's expansion phase before collapsing! :) gentlemen, let me remind you (without the moderator tag) to please keep the thread civil. i detect a bit of leaning towards roughage and baseless FUD throwing, which will only lead to flaming. | |
Strangely enough, though, the star actually gets brighter, despite getting cooler, and the fusion process it slips into - fusing helium - actually produces more heat then fusing hydrogen!
This extra heat forces the start to expand - all stars are balanced precariously between collapsing in on itself due to gravity, and expanding massively, due to the radiation produced by fusion. Increasing the outwards pressure increases the star's size - and that's what fusing helium does. But the extra energy input is linearly related to the previous size of the star, and the extra surface area due to expansion is n^2. So the surface area/energy ratio is lower then it was before, which means a lower temperature. But because the brightness of the star depends on surface area and temperature, it still gets brighter. Interesting, hmm? | |
Artekia wrote:
One thing I'm curious about, if matter can convert to energy, can the reverse apply? Can energy create matter? DO NOT QUESTION ENTROPY THE SYSTEM IS PERFECT | |
I know it's wrong to backseat moderate but if it's alright with you can this topic be split into two? WMDs mixed with astronomy is making one heck of a large thread and it's actually difficult for me to load the page now, much less catching on one topic in between another.
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Jp wrote:
Actually, stellar expansion is caused by the shift to fusing helium - it produces more thermal energy then the proton-proton cycle, which produces a larger outwars force to counter gravity. (edit) I went and dug up some information that talks about this, though it just says it happens and not why. Do you know of any sources which explain this in any better detail? I'm going to try and figure this one out, since it seems odd that the star would save up its helium until after it's done fusing its hydrogen. (/edit) <s>Most everything I post about is from memory (which is why I almost never bother to post links about what I say), and the things I have read and watched about this did not mention that, at least not that I recall. Where did you get that information from? I don't see how a star could suddenly shift from fusing hydrogen to fusing helium. If it's going to fuse helium at all, it seems like it should be doing so as the helium is being generated instead of saving it up for the end. If this really is the case, this odd turn of events intrigues me and I must do some research. If you are getting your information from Wikipedia on this one though, I don't trust it for specific details such as these. I've seen too much inaccurate data in there to trust it on anything except generic descriptions. It is too easy for anyone to come along and make it say whatever they want (Like that oh so informative addition to the thermite page. I won't mention any names there; you know who you are.) Off to the encyclopedia I go.</s> And the Earth would be toast before hitting the 'atmosphere' of the Sun - it would have to pass through the Roche limit first, and get torn to shreds by tidal forces. Yes, I mentioned that too. | |
Yes, and that is how we have made a lot of our more recent discoveries about physics. In fact, it is currently the only way we have regular access to some particles, such as antiprotons. We create them in particle accelerators.
To put it simply, we accelerate particles to such high speeds that their kinetic energy is greater than the mass-energy of a particle. Then, when they bombard stationary particles and are slowed, the excess kinetic energy is converted into new matter. Unfortunately though, since particle accelerators are so expensive, we have to take shortcuts in construction and their efficiency becomes terrible. | |
Destroy the planet, not blow it up. They have different meanings in my view. I tend to see things differently than others do. And I didn't really ask your opinion, but thanks. Just makes me a bit more knowledgeable.
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I'm getting it from a variety of physics/science books. Notably, Physics for Scientists and Engineers, 3rd edition, volume 2, by Douglas c. Giancoli. Page 1148, if you're that interested. :P
Also, The Science of the Discworld, by Terry Pratchett, Ian Stwart, and Jack Cohen. That's a less serious/quantitative source, though, and it's older, too - it should be considered secondary to the textbook I mentioned. The reason the star waits until it's mostly out of hydrogen is because fusion reactions need a certain baseline energy before they take place. The fusion of hydrogen doesn't give the star enough heat to start fusing helium, not even in the core. Once the star is mostly out of hydrogen, it starts shrinking under gravity, which converts gravitational potential energy into kinetic energy - in the form of temperature. So the core heats up as it shrinks until it gets to the point where it begins fusing helium, and that produces the outward pressure needed to force the star out - as well as providing enough energy to sustain helium fusion. So then the star fuses helium in the core, and continues to fuse hydrogen towards its surface. Then when it runs out of helium, the process repeats for the next few higher elements, and so on, until the star starts trying to fuse iron. Fusing (or fissioning) iron takes energy, rather then providing it, so the star collapses in on itself and releases a helluva lot of energy, all at once - a supernova. Not all stars are big enough to get to that point, of course. I love physics. :P | |
Well, it's not released as energy because of that equation, but the equation does show how much energy is released and that matter can be converted into energy. I know like nothing about physics, but I'm guessing all the nuclear reactions going on gradually deplete the matter.