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  #1  
Old 09-21-2012, 12:23 AM
TSBG TSBG is offline
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Putting out the Sun with ice cubes

Column:

http://www.straightdope.com/columns/...ut-out-the-sun

This might be the best column of all time. A proper level of non-strained humor, with a real and surprising answer to a question well beyond the reach of Google. Huzzah.
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  #2  
Old 09-21-2012, 12:52 AM
eschereal eschereal is offline
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Thanks for posting that. Looks like we will have to give up on that strategery for fighting globular warming. Next?
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Old 09-21-2012, 08:41 AM
chrisk chrisk is offline
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Yeah, that's a fun question. My followup is to Una, asking about one critical assumption: How cold is the ice cube? I would think it would matter somewhat if we're taking about 'so warm it's melting' ice or 'fraction of a degree above absolute zero' ice - in terms of being able to temporarily halt fusion by reducing the sun's core temperature, that is.
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  #4  
Old 09-21-2012, 09:17 AM
Lumpy Lumpy is offline
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Suppose you could cool the sun by some kind of magic freeze ray, and keep cooling it as it contracted under it's own gravity. Would you eventually get a ball of superdense but too-cold-to-fuse hydrogen? Or would you reach a point where the hydrogen would be dense enough to start fusing even if it started out at just 1 degree Kelvin?
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  #5  
Old 09-21-2012, 11:41 AM
Una Persson Una Persson is offline
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Originally Posted by chrisk View Post
Yeah, that's a fun question. My followup is to Una, asking about one critical assumption: How cold is the ice cube? I would think it would matter somewhat if we're taking about 'so warm it's melting' ice or 'fraction of a degree above absolute zero' ice - in terms of being able to temporarily halt fusion by reducing the sun's core temperature, that is.
I assumed 0 F. However, it makes little difference to the calculations what you assume for the ice, as you're quenching something so many orders of magnitude hotter that a few dozen degrees one way or the other fall out in the error band. Even accounting for the heat of fusion and heat of vaporization doesn't compare much with the sensible heat of raising the water, steam, then plasma to 10,000,000 C.
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Old 09-21-2012, 11:56 AM
Czarcasm Czarcasm is online now
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How much dry ice would it take?
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  #7  
Old 09-21-2012, 01:53 PM
Deeg Deeg is offline
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Why is nickel and iron incapable of undergoing fusion?
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  #8  
Old 09-21-2012, 01:59 PM
Gagundathar Gagundathar is online now
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That was truly a classic SD article.
Una, the next time you speak with Cecil please remind him, for me, that he rocks!
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  #9  
Old 09-21-2012, 02:27 PM
Alan Smithee Alan Smithee is offline
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Damn, I came in as well to compliment Cecil on an excellent article. He's been on a roll lately, I think, but this one is really classic. Maybe the competition from Randall Munroe has inspired him!
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  #10  
Old 09-21-2012, 02:35 PM
Malacandra Malacandra is offline
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Originally Posted by Deeg View Post
Why is nickel and iron incapable of undergoing fusion?
Things only fuse if you make energy out of the deal. Similarly, things only fission if you make energy out of the deal. Nickel and iron don't have any fission or fusion products that would be lower-energy than them, so they can't do either. Of course, things can happen if you have a large energy excess, such as in a supernova - that's the only reason why fissionable elements exist, they would never result from normal fusion. Just as oil and coal are fossilised sunshine, uranium is fossilised supernova.

Last edited by Malacandra; 09-21-2012 at 02:37 PM..
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  #11  
Old 09-21-2012, 02:49 PM
Michael63129 Michael63129 is offline
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Some people believe that you can get energy out of nickel fusion. Of course, as far as I know, their claims haven't been verified (some suggest that, assuming fusion is indeed occurring, the hydrogen fuses, although the reaction is supposed to produce copper).
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Old 09-21-2012, 03:15 PM
TriPolar TriPolar is offline
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I thought the problem was that fusion in the heavier elements required more energy than it produced. Someone please enlighten me.

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  #13  
Old 09-21-2012, 03:23 PM
gnoitall gnoitall is online now
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Originally Posted by Malacandra View Post
Things only fuse if you make energy out of the deal. Similarly, things only fission if you make energy out of the deal. Nickel and iron don't have any fission or fusion products that would be lower-energy than them, so they can't do either. Of course, things can happen if you have a large energy excess, such as in a supernova - that's the only reason why fissionable elements exist, they would never result from normal fusion. Just as oil and coal are fossilised sunshine, uranium is fossilised supernova.
The Wikipedia article about Nuclear Binding Energy has a graph that illustrates the mechanical reason for this. Nuclear binding energy, as the name implies, is the energy that binds subatomic particles (nucleons) in the nucleus of the atom. It's a very short-ranged attractive force; in a large atom (like uranium), the binding force of a given proton or neutron may not reach all the way to the most distant other particles in the same nucleus; at the same time, the electrostatic repulsion among all the protons tends to push the nucleus apart a tiny bit. This puts a limit as to how strongly-bound a large nucleus can be, and explains why some very heavy atoms can be split (they're weakly bound and have internal repulsion pressures). On the other hand, a nucleus with too few particles doesn't have as much total binding energy as a more massive one, because there are just fewer particles. It also means that the lighter nuclei can accept more particles by fusion.

The peak in the curve between "low per-particle binding energy because of too few particles" and "low per-particle binding energy because of too many particles" is in the vicinty of Nickle-62 and Iron-56. This is the "sweet spot" in the binding energy curve, in which the atom is not too small and not too big, but just right. It actually takes more energy to disrupt the balanced nuclear binding than can be liberated by breaking the binding force.

If a star begins to pour energy into nickle-iron fusion, it's a doomed exercise. Nickle-iron fusion sucks up all the energy you care to put into it and comes back for more. It takes, and takes, and takes.

(This has to be a big star, around a dozen to a few dozen times more massive than the Sun. There's not enough mass for a smaller star to burn into such massive core elements as silicon.)

Since energy is the ultimate thing resisting the huge gravity of the entire mass of a star, when the energy is gone, gravity takes over. The entire mass of the star's inner layers accelerates towards the center and compresses into a humougous instantanous explosion: a core-collapse supernova.

Good summary article specifically about the Iron peak of nuclear binding. Relevant quote:
Quote:
For elements before iron, nuclear fusion releases energy. For elements heavier than iron, nuclear fusion consumes energy, but nuclear fission releases it.
Left unstated, elements around iron can't be fissioned or fused profitably. (Or at all? I've never heard of fissioning anything as stable as iron.)
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  #14  
Old 09-21-2012, 04:15 PM
Deeg Deeg is offline
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Awesome explanations, thanks all!
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Old 09-21-2012, 04:38 PM
Chronos Chronos is online now
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I wonder if Cecil (and Una) might have left something out. Tossing ice cubes into the Sun will add more hydrogen, true, but it'll also add more oxygen. While it's true that oxygen will fuse under the right conditions, the core of the Sun isn't those conditions, and too much non-fusing material will "poison" the reaction. A sunlike star can only fuse about 10% of its total hydrogen supply before the helium is enough to start having drastic effects; surely adding material that's 1/3 nonfusible by atom count will hurt more than it'll help.
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  #16  
Old 09-21-2012, 05:14 PM
gnoitall gnoitall is online now
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Originally Posted by Chronos View Post
I wonder if Cecil (and Una) might have left something out. Tossing ice cubes into the Sun will add more hydrogen, true, but it'll also add more oxygen. While it's true that oxygen will fuse under the right conditions, the core of the Sun isn't those conditions, and too much non-fusing material will "poison" the reaction. A sunlike star can only fuse about 10% of its total hydrogen supply before the helium is enough to start having drastic effects; surely adding material that's 1/3 nonfusible by atom count will hurt more than it'll help.
Oxygen is heavier per-atom than hydrogen or helium. The massive gravitation gradiant of a star's innards means that elements are sorted pretty efficiently by atomic mass, so all the oxygen would sink deeper into the core (past the helium "waste" of hydrogen-burning fusion) and sit there inert until temperatures increased high enough to start it fusing... much later in the life of a main-sequence star.
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  #17  
Old 09-21-2012, 05:30 PM
Lumpy Lumpy is offline
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Quote:
Originally Posted by Chronos View Post
I wonder if Cecil (and Una) might have left something out. Tossing ice cubes into the Sun will add more hydrogen, true, but it'll also add more oxygen. While it's true that oxygen will fuse under the right conditions, the core of the Sun isn't those conditions, and too much non-fusing material will "poison" the reaction. A sunlike star can only fuse about 10% of its total hydrogen supply before the helium is enough to start having drastic effects; surely adding material that's 1/3 nonfusible by atom count will hurt more than it'll help.
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Oxygen is heavier per-atom than hydrogen or helium. The massive gravitation gradiant of a star's innards means that elements are sorted pretty efficiently by atomic mass, so all the oxygen would sink deeper into the core (past the helium "waste" of hydrogen-burning fusion) and sit there inert until temperatures increased high enough to start it fusing... much later in the life of a main-sequence star.
If all the oxygen settled into the sun's core, wouldn't it form a denser core that would stimulate hydrogen fusing at it's boundary, the way mainstream stars become red giants once they accumulate enough "ash"?
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Old 09-21-2012, 05:32 PM
Una Persson Una Persson is offline
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Originally Posted by gnoitall View Post
Oxygen is heavier per-atom than hydrogen or helium. The massive gravitation gradiant of a star's innards means that elements are sorted pretty efficiently by atomic mass, so all the oxygen would sink deeper into the core (past the helium "waste" of hydrogen-burning fusion) and sit there inert until temperatures increased high enough to start it fusing... much later in the life of a main-sequence star.
That is sort of the thought experiment we went through. However, I admit there was some significant uncertainty in this speculation.
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  #19  
Old 09-21-2012, 05:49 PM
gnoitall gnoitall is online now
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If all the oxygen settled into the sun's core, wouldn't it form a denser core that would stimulate hydrogen fusing at it's boundary, the way mainstream stars become red giants once they accumulate enough "ash"?
Possibly. I think the greater effect will be the addition of matter. A lot of matter. As the article itself indicates, more than 1/3 of the mass of the sun. That's a lot of mass. In the case of the sun, enough to push it into the next luminosity class (F5 or F4 versus current G2), becoming hotter and a little whiter. Global warming-wise, CO2 has nothing on that.
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  #20  
Old 09-21-2012, 08:00 PM
Steve MB Steve MB is online now
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Originally Posted by gnoitall View Post
Left unstated, elements around iron can't be fissioned or fused profitably. (Or at all? I've never heard of fissioning anything as stable as iron.)
Nuclei can be pushed the "wrong way" on the binding energy curve with sufficient energy input. For instance, the artificial elements at the ass end of the periodic table are created by slamming lighter nuclei together, causing them to fuse with a net energy loss. On a larger scale, elements heavier than iron exist because the energy levels found in supernova explosions push fusion beyond the bottom of the binding energy curve.
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  #21  
Old 09-22-2012, 12:47 AM
gnoitall gnoitall is online now
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Nuclei can be pushed the "wrong way" on the binding energy curve with sufficient energy input. For instance, the artificial elements at the ass end of the periodic table are created by slamming lighter nuclei together, causing them to fuse with a net energy loss. On a larger scale, elements heavier than iron exist because the energy levels found in supernova explosions push fusion beyond the bottom of the binding energy curve.
Fusion, sure. The catastrophic runaway fusion in the last few moments of a star's existence before death in a nova or a supernova spawns all of the naturally-occurring elements heavier than iron. Again, it's not exothermic--it sucks down energy like I drink bourbon, but in those moments there's ample energy to spare from the cataclysmic kinetic energy of super-dense plasma colliding with itself at a significant fraction of lightspeed (in the case of a Type II supernova).

No, I was more wondering about fissioning stable "iron peak" elements. Everything I've read seems to talk about fission in the heaviest parts of the periodic table.
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  #22  
Old 09-22-2012, 01:15 AM
eschereal eschereal is offline
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Originally Posted by Lumpy View Post
Suppose you could cool the sun by some kind of magic freeze ray, and keep cooling it as it contracted under it's own gravity. Would you eventually get a ball of superdense but too-cold-to-fuse hydrogen? Or would you reach a point where the hydrogen would be dense enough to start fusing even if it started out at just 1 degree Kelvin?
What you would get depends on how good your magic freeze ray is. If you can extract every bit of energy all the way to the core (quite a challenge with a very massive object like a star), it seems to me that electrostatic repulsion would eventually be overcome by weak-force binding, probably resulting in a big ball of "neutronium" (a giant atomic nucleus or neutron star). If, as would seem likely, you can only effectively draw heat off the surface, the increasing pressure of compaction would make the core get hotter. You would have to continually draw off an increasing amount of energy to get enough pressure-driven heat out of the center to prevent ignition. Where you would put that energy is a troubling question in and of itself (even "magic" has limitations).

Then, of course, you have general relativity to deal with. As the star contracts, its gravitational gradient gets steeper, causing time to dilate more toward the center. Your energy extraction must accelerate greatly to keep up with the difference in your frame of reference. At a rate that is not comparable to a supernova (which quickly blows off a lot of mass as it collapses), I doubt you could reach the neutronium threshold, meaning you would have a rather unstable ball of hydrogen and other stuff. But space is not an inert, empty void, there is lots of energy in the sparest vacuum, and some of it will get to tickling the core of your frozen star. It would not take much under those conditions. Ignition looks like it would be all but inevitable.
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  #23  
Old 09-22-2012, 08:34 AM
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Originally Posted by Lumpy View Post
Suppose you could cool the sun by some kind of magic freeze ray,
The magic ray, would be a laser beam. Laser cooling the sun.

Quote:
and keep cooling it as it contracted under it's own gravity. Would you eventually get a ball of superdense but too-cold-to-fuse hydrogen? Or would you reach a point where the hydrogen would be dense enough to start fusing even if it started out at just 1 degree Kelvin?
I'm not sure, but I would imagine that the force of gravity would be enough pressure to ignite fusion, even if you did cool the sun.
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  #24  
Old 09-23-2012, 11:27 PM
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An ice cube with 1/3 the mass of the sun

In Cecil's column on putting out the sun with ice cubes, at http://www.straightdope.com/columns/...ut-out-the-sun , the Master says:

Quote:
One last thing. The cosmic ice cube posited above would have one-third the mass of the sun. Left floating in space and given enough time to compact itself, it would eventually heat to the point of fusion and become its own little sun. A mere 0.08 solar masses is required for this purpose.
I must protest, sir!

A ball of gas 0.08 solar masses can, indeed, form a small and very dim (red dwarf) star, with hydrogen fusion going on in its teensy-weensy core. However, this assumes that said ball of gas consists primarily of hydrogen, i.e. about 75% hydrogen. An ice cube, being frozen water, is only 11% hydrogen by mass -- the rest being oxygen.

I submit to you that a 0.08 solar mass ball of water -- or even a 0.33 solar mass ball of water -- would have too low a hydrogen concentration to sustain nuclear fusion at its core, even if the material that formed the ball infell from an infinite height.
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Old 09-24-2012, 12:19 AM
Little Nemo Little Nemo is online now
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I'm not an astrophysicist but I thought any element would achieve nuclear fusion if it was raised to a high enough pressure and temperature. Is hydrogen required for the process?
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  #26  
Old 09-24-2012, 03:41 AM
AaronX AaronX is offline
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Iron is the most stable element. Heavier elements fission, lighter elements fuse.
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  #27  
Old 09-24-2012, 07:22 AM
Der Trihs Der Trihs is offline
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I'm not an astrophysicist but I thought any element would achieve nuclear fusion if it was raised to a high enough pressure and temperature.
I'm not astrophysicist either, but as far as I know it takes a massive star to fuse oxygen.

And more massive elements than even iron can fuse - it's just a process that consumes energy instead of producing it for iron and anything more massive.
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Old 09-24-2012, 12:48 PM
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The magic ray, would be a laser beam. Laser cooling the sun.
And how would that work? A laser would add energy, not subtract it.

Now if you could somehow make the Sun generate a laser, and pump that energy out via the laser, that would be some mega powerful laser, cutting across the galaxy like a hot knife through butter. But wouldn't that take something like a core collapse?

Note: it would have to be a significantly powerful laser output to be more than the Sun is already dumping via electromagnetic radiation.

Last edited by Irishman; 09-24-2012 at 12:49 PM..
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Old 09-24-2012, 01:57 PM
John W. Kennedy John W. Kennedy is offline
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And how would that work? A laser would add energy, not subtract it.

Now if you could somehow make the Sun generate a laser, and pump that energy out via the laser, that would be some mega powerful laser, cutting across the galaxy like a hot knife through butter.
Paging Kimball Kinneson!
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Old 09-24-2012, 02:13 PM
Una Persson Una Persson is offline
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I submit to you that a 0.08 solar mass ball of water -- or even a 0.33 solar mass ball of water -- would have too low a hydrogen concentration to sustain nuclear fusion at its core, even if the material that formed the ball infell from an infinite height.
The assumption would be that the mass requirement of 0.08 is dictating the amount of material needed for the density to increase to a point where the temperature could increase enough to ignite fusion. So in this case the ice cube could still slowly collapse and heat up to above the required temperature. Now what happens as that occurs is a good question. The assumption was that since this would happen slowly the molecules would free up their atoms and then the atoms form a plasma state, and in that plasma state the density difference would migrate the oxygen to the center, while the hydrogen formed a shell around it. While on a mass basis the hydrogen would be smaller than the oxygen, on a volumetric basis the resulting protostar would be mostly hydrogen. So would the hydrogen portion be dense enough or hot enough to ignite? Maybe, maybe not.

It's also possible that given the time required, starting with a solid object collapsing rather than a gas cloud, I wonder if enough heat or radiation might be radiated away before the temperature rose to the proper level.
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  #31  
Old 09-24-2012, 03:52 PM
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There's already been a thread posted about this column.

Putting out the Sun with ice cubes.

I've requested a merge.
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Old 09-24-2012, 03:58 PM
Dr. Strangelove Dr. Strangelove is offline
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And how would that work? A laser would add energy, not subtract it.
Laser cooling is a thing. It works quite well for single atoms and molecules, although apparently progress is also being made on laser cooling of macroscopic objects (unfortunately, the most recent research I can find on the subject is a few years old).

Good luck scaling that up to a star size...
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Old 09-24-2012, 04:09 PM
Der Trihs Der Trihs is offline
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And how would that work? A laser would add energy, not subtract it.

Now if you could somehow make the Sun generate a laser, and pump that energy out via the laser, that would be some mega powerful laser, cutting across the galaxy like a hot knife through butter. But wouldn't that take something like a core collapse?

Note: it would have to be a significantly powerful laser output to be more than the Sun is already dumping via electromagnetic radiation.
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Paging Kimball Kinneson!
Or Speaker -To-Animals.



"With such a weapon I could vaporize the Earth!"

"Speaker!"

"It was a natural thought, Louis."
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Old 09-24-2012, 04:28 PM
gnoitall gnoitall is online now
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Or Speaker -To-Animals.



"With such a weapon I could vaporize the Earth!"

"Speaker!"

"It was a natural thought, Louis."
Good point. Niven did use a magnetically-induced induced coronal mass ejection event plus magnetic containment to make the Ringworld's sun lase as a system-wide self-defense system. I admired the chutzpah of making your star into one big laser pump.
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Old 09-24-2012, 08:01 PM
Little Nemo Little Nemo is online now
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Originally Posted by Una Persson View Post
The assumption would be that the mass requirement of 0.08 is dictating the amount of material needed for the density to increase to a point where the temperature could increase enough to ignite fusion. So in this case the ice cube could still slowly collapse and heat up to above the required temperature. Now what happens as that occurs is a good question. The assumption was that since this would happen slowly the molecules would free up their atoms and then the atoms form a plasma state, and in that plasma state the density difference would migrate the oxygen to the center, while the hydrogen formed a shell around it. While on a mass basis the hydrogen would be smaller than the oxygen, on a volumetric basis the resulting protostar would be mostly hydrogen. So would the hydrogen portion be dense enough or hot enough to ignite? Maybe, maybe not.

It's also possible that given the time required, starting with a solid object collapsing rather than a gas cloud, I wonder if enough heat or radiation might be radiated away before the temperature rose to the proper level.
Sounds like the makings for the most explosive episode of MythBusters EVER!
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  #36  
Old 09-24-2012, 10:02 PM
Steve MB Steve MB is online now
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Originally Posted by tracer View Post
A ball of gas 0.08 solar masses can, indeed, form a small and very dim (red dwarf) star, with hydrogen fusion going on in its teensy-weensy core. However, this assumes that said ball of gas consists primarily of hydrogen, i.e. about 75% hydrogen. An ice cube, being frozen water, is only 11% hydrogen by mass -- the rest being oxygen.

I submit to you that a 0.08 solar mass ball of water -- or even a 0.33 solar mass ball of water -- would have too low a hydrogen concentration to sustain nuclear fusion at its core, even if the material that formed the ball infell from an infinite height.
Is the controlling factor proportion by mass (11%) or proportion by number of nuclei (67%)?
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  #37  
Old 09-28-2012, 01:38 PM
YogSosoth YogSosoth is offline
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I just wanted to say that I really liked this article Very well written
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  #38  
Old 09-30-2012, 07:39 AM
C K Dexter Haven C K Dexter Haven is offline
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MOD NOTE: There were two threads on the same topic (although slightly different slants) which I've now merged. That possibly makes for a little bit of discontinuity in the fabric of space-time (well, at least in the reading of the now merged thread.) Please be sure to QUOTE the material that you're commenting on, so as to avoid future confusions.
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  #39  
Old 10-02-2012, 12:49 PM
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XKCD what if? Looked into putting out the sun with water this week.
http://what-if.xkcd.com/14/
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  #40  
Old 10-02-2012, 01:09 PM
gnoitall gnoitall is online now
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XKCD what if? Looked into putting out the sun with water this week.
http://what-if.xkcd.com/14/
Yeah. Eerie coincidence, or what?

Should I be worried that I arrived at approximately the same conclusion as Randall et al.?
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Old 10-02-2012, 08:19 PM
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XKCD what if? Looked into putting out the sun with water this week.
http://what-if.xkcd.com/14/
Slight hijack, but the question about opening a portal between Mexico City and Boston ignores gravitational potential (not to even mention the difference in velocity due to the Earth's rotation). If the air from Boston had to not only move through the portal but also make up the altitude difference, the rate of flow would be zero- the same as air in equilibrium at any spot on Earth.
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  #42  
Old 10-03-2012, 09:48 AM
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Originally Posted by Lumpy View Post
Slight hijack, but the question about opening a portal between Mexico City and Boston ignores gravitational potential (not to even mention the difference in velocity due to the Earth's rotation). If the air from Boston had to not only move through the portal but also make up the altitude difference, the rate of flow would be zero- the same as air in equilibrium at any spot on Earth.
Portals are going to be ignoring a lot of physics no matter what. So you have to go with some basic assumptions about how portals work. Unless otherwise specified in this day and age portals work like they do in the game Portal. Those function basically as doors your velocity with respect to one side of the door are translated through to the other side. Which basically ignores things like the relative motion of the portals to each other and the potential energy due to position. This is consistent with most portals in fiction. Some teleportation stories will discuss the potential energy issues but almost all ignore velocity differences due to being on a rotating body.

Side note teleportation is not in the default chrome dictionary.
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Old 10-12-2012, 12:33 PM
DHMO DHMO is offline
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Don't forget the C-N-O cycle!

One critical issue frequently left out of these discussions on "extinguishing" the Solar furnace with water (or ice) is that, in addition to adding Hydrogen fuel to the fusion reaction, the Oxygen (rather than settling to the center as a relatively "inert" substance or being part of an Oxygen-Oxygen fusion reaction) takes an active role as a catalyst for the fusion reaction in the CNO Cycle.

In stars the mass of the Sun, the Proton-Proton reaction predominates, but a small percentage of the energy output is produced via the CNO Cycle. At about 1.3 Solar masses, the CNO Cycle is the dominant source of energy. If sufficient water (in whatever state) were added to have any potential for damping the Sun's fusion reaction, it would push the total mass of the Sun high enough to make the CNO Cycle a much greater proportion of the energy produced.
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