What force is created before supernova explosion?

  • #1

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how antigravity force is created before supernova explosion? why it is not created in a body less than chandrashekhar limit?
 

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  • #2
wabbit
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What do you mean by "antigravity force" ?
 
  • #3
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I think he means an outward force so big that the whole star expands.


And in that case it is produced in every single star in the universe other than brown and red dwarfs(brown and red dwarfs just gradually die off like how a battery gradually dies off so no outward force other than the one produced by fusion is involved) from small ones like our sun that will never supernova to large ones like betelgeuse that will definetely supernova within the next 10,000 years.
 
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  • #4
wabbit
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Ah you lost me here, what is this outward force you are referring to ?

Also, do you have a reference to the fact that Betelgeuse will go supernova in the next 10,000 years ? This seems extremely precise, I wonder how we can get such accuracy ?
 
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  • #5
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This outward force that I am referring to is the pressure produced by the star's core to counteract gravity which always trys to shrink the star. When you have a massive star(more massive than our sun) at some point pressure is greater than gravity so the star expands. Before that though some stars will actually shrink right before helium fusion starts. This is a helium flash. Then after years of being a red giant or supergiant(and in rare cases hypergiant(hypergiants are the biggest stars in the universe)) the pressure gets so big that while the core contracts due to gravity forming a neutron star or if the star is supermassive, a black hole the outer layers continue to expand at a rapid pace. This is a type II supernova
 
  • #6
wabbit
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OK I see - pressure is nothing one would call antigravity, but also, as I understand it this is not what causes a supernova explosion. On the contrary, if I recall correctly, it is insufficient pressure to counteract gravity that provokes a collapse, and the explosion is the resulting rebound. Describing this as antigravity seems very weird, if anything the force causing the explosion is gravity.

Regarding Betelgeuse, I found this article, which is reporting on http://arxiv.org/abs/1406.3143 : Evolutionary tracks for Betelgeuse (Michelle M. Dolan, Grant J. Mathews, Doan Duc Lam, Nguyen Quynh Lan, Gregory J. Herczeg, David S. P. Dearborn). They estimate ~100k years, which seems quite precise already. Very interesting stuff.
 
  • #7
Vanadium 50
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Roughly 20x as much writing has been expended guessing what the OP means. Why not wait for him to explain what he means?
 
  • #8
Chronos
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The outward force in a supernova is created by matter recoiling from the degenerate core during collapse. There are also significant neutrino emissions involved as well - no antigravity required.
 
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  • #9
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how antigravity force is created before supernova explosion? why it is not created in a body less than chandrashekhar limit?
Below is a good brief description of what goes on in a red supergiant just before supernova-
http://aether.lbl.gov/www/tour/elements/stellar/stellar_a.html

I suppose you could say that it is the mass of the original star that results in there being a supernova or not. A star with an original mass of up to 8 sol will result in a white dwarf, a star with an original mass of between 8 and 18 sol will result in a supernova & neutron star, and a star with an original mass of more than 18 sol will result in a supernova & black hole.

source-
http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit3/extreme.html
 
  • #10
A Hypothetical question: What would happen to our solar system if there is a supernovae exploding at a distance of our closest star Proxima Centauri at approx 4.2 light years away? What would be the consequences?
 
  • #11
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A Hypothetical question: What would happen to our solar system if there is a supernovae exploding at a distance of our closest star Proxima Centauri at approx 4.2 light years away? What would be the consequences?
It really depends on what kind of supernova explosion takes place. In general, supernovae release huge amounts of x-rays and gamma rays, and these could significantly damage the ozone layer in the atmosphere when they reach the Earth. A depletion of the ozone layer could have catastrophic effects for the biosphere, as primary producers would significantly be affected after exposure UV radiation from the Sun, which could lead to a collapse in food webs globally.
I'm not 100% sure, but IMO the radiation should affect human satellites near Earth as well.
 
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  • #12
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A Hypothetical question: What would happen to our solar system if there is a supernovae exploding at a distance of our closest star Proxima Centauri at approx 4.2 light years away? What would be the consequences?
The blast from a supernova can be somewhat directional, so the exact consequences for Earth could vary because of that,
However even if Earth were located well away from the regions of maximum blast, I'm pretty sure that the amount of gamma radiation received from a supernova that close to Earth would likely sterilize all life, and probably fry the atmosphere into a highly ionized state.
 
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  • #13
What do you mean by "antigravity force" ?
the outward force that is created during supernova explosion is antigravity force.. at that time gravity collapses.
 
  • #14
Drakkith
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the outward force that is created during supernova explosion is antigravity force.. at that time gravity collapses.
The outward force certainly works against gravity, but it is not antigravity in the usual sense of the word. Not anymore than the thrust propelling a rocket away from Earth is antigravity.
 
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  • #16
SteamKing
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the outward force that is created during supernova explosion is antigravity force.. at that time gravity collapses.
You were misinformed somewhere. Gravity doesn't "collapse" during the microseconds preceding the supernova event.

If anything, once fusion stops in the core of the star, gravity is able to cause the core to compress to a tiny fraction of its original size, since there is nothing, no force, which counteracts it.

You should read something about supernova formation, to get the correct idea about the sequence of events:

http://en.wikipedia.org/wiki/Type_II_supernova
 
  • #17
Ken G
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That Wiki entry promotes some common misconceptions. I knew it would, it's not alone there-- textbooks say similarly misleading things. But it's worth pointing them out to try to set the record straight. For example, the Wiki says "As there is no fusion to further raise the star's temperature to support it against collapse, it is supported only by degeneracy pressure of electrons." This is incorrect, it is never necessary to raise temperature to support against collapse, what you actually need to support against collapse is to maintain the temperature-- you need to replace lost heat. When lost heat is not replaced, what actually happens is temperature rises, so we can see that a constant temperature is a sign of something that is being supported, and a rising temperature is a sign of something that is not being supported. Worse, the Wiki goes on to say "In this state, matter is so dense that further compaction would require electrons to occupy the same energy states."
That's also incorrect, further compaction is certainly possible if sufficient work is supplied, degeneracy never prevents collapse any differently from any other kind of pressure, it simply sets the requirements for collapse like any pressure does. Degeneracy pressure is, in that sense, a completely mundane type of pressure, and a natural aspect of pressure is that work is required to produce compaction. But like with any nonrelativistic gas pressure, the work that would be supplied to produce compaction causes an increase in pressure which exceeds the increase in gravity, this is normal gas-pressure stability no different from an ideal gas. So it bounces back-- gravity does not contract gas pressure supported objects unless there is net heat loss. So what neutron degeneracy really does, which has no direct connection with producing pressure, is to eliminate further heat loss, and gravity always requires heat loss in order to obtain further contraction. Degeneracy is a thermodynamic effect that inhibits heat loss, not a mechanical effect that produces pressure.
 
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  • #18
Drakkith
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When lost heat is not replaced, what actually happens is temperature rises, so we can see that a constant temperature is a sign of something that is being supported, and a rising temperature is a sign of something that is not being supported.
Note that Ken's referring to the Kelvin-Helmholtz mechanism here. (I think)
 
  • #19
Ken G
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Right. That mechanism says that if there is net heat loss, gravity will slightly exceed pressure. It is a misconception to say that the heat loss ever causes temperature drop, however-- the temperature can rise monotonically everywhere, throughout the process. The key is that the slight excess of gravity is always causing contraction, allowing gravity to do work that pumps kinetic energy into the system-- usually at a rate twice as large as the net heat loss that is driving the whole business. Thus the excess kinetic energy piles up and causes the continuing temperature rise, but even though the temperature is steadily rising, the rising gravity continues to slightly exceed the pressure.

Anything that short-circuits the net heat loss will stop this process, and either fusion or degeneracy can do that-- fusion by replacing lost heat, degeneracy by preventing heat loss in the first place.
 
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  • #20
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The "outward force" is caused by electron degeneracy. It can resist further compression by the gravity of the star. Bigger stars could overcome even that and create black holes.
 
  • #21
Ken G
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The "outward force" is caused by electron degeneracy. It can resist further compression by the gravity of the star. Bigger stars could overcome even that and create black holes.
That is certainly a standard way to describe the situation, but I am pointing out the potential for that language to lead to misconceptions. In strict terms, the only gross macroscopic effect of degeneracy is the inhibition of heat loss, and as such it does not "cause" an outward force. (It also inhibits internal collisions, so it conducts heat very efficiently, but that just redistributes excess heat, most of the internal kinetic energy is still insulated against any heat loss.)

Admittedly, what constitutes a "cause" is not necessarily cut-and-dried in science, but let me offer this analogy. Take a hot ball of self-gravitating ideal gas, say a protostar, prior to any fusion. Now surround it with a big mirror, so no heat can escape. That protostar will quickly cease contracting. Would we say that the mirror is causing the outward force in that star, that prevents it from collapsing? The role of degeneracy in a white dwarf or neutron star is quite similar to that mirror-- it is the reason there is no further contraction, but it is not the cause of the outward force. The cause of the outward force is the internal kinetic energy of the particles, and nothing else.

So what happens in bigger stars? The neutrons go relativistic. It turns out that relativistic kinetic energy is never good at producing pressure that can resist gravitational contraction, because then gravitational contraction only supplies an equal amount of energy as needed for the increasing pressure to keep pace with the increasing gravity (so continues to lag behind if out of balance), rather than providing twice that amount as happens in nonrelativistic gas (so causes the pressure to eventually rise up and exceed gravity, as happens in a core bounce). That fact has nothing to do with degeneracy, degeneracy only tells you if heat loss will be stopped before the gas goes relativistic. If the gas has already gone relativistic, degeneracy is of no importance.
 
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  • #22
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the outward force that is created during supernova explosion is antigravity force.. at that time gravity collapses.
The following is an extract from the first link in post #9 which describes what happens just before supernova-

As the fusion process continues, the concentration of Fe increases in the core of the star, the core contracts, and the temperature increases again. When the temperature reaches a point where Fe can undergo nuclear reactions, the resulting reactions are different than the ones that have previously taken place. Fe nuclei are the most stable of all atomic nuclei. Because of this, when they undergo nuclear reactions, they don't release energy, but absorb it. Therefore, there is no release of energy to balance the force of gravity. In fact, there is actually a decrease in the internal pressure that works with gravity to make the collapse of the core more intense. In this collapse, the Fe nuclei in the central portion of the core are broken down into alpha particles, protons, and neutrons and are compressed even further. However, they cannot be infinitely compressed. Eventually, the outer layers of material rebound off the compressed core and are thrown outward. This situation can be likened to a rubber ball on the ground that is struck with a hammer. Initially the hammer can compress the rubber ball because of its force, but eventually it is stopped by the density and pressure of the rubber ball reaching its limit, and is thrown back violently by the recoiling rubber ball, which itself will bounce off the surface because of this recoil. In the star, the outer layers of the core are like the hammer, and the core is the rubber ball. Following the collapse of the inner core, the outer layers of the star are pulled toward the center. This sets the stage for a tremendous collision between the recoiling core layers and the collapsing outermost layers. Under the extreme conditions of this collision, two things happen that lead to the formation of the heaviest elements. First, the temperature reaches levels that cannot be attained by even the most massive stars. This gives the nuclei present large kinetic energies, making them very reactive. Second, because of the breaking apart of the iron nuclei in the central core, there is a high concentration of neutrons (called the neutron flux) that are ejected from the core during the supernova. These neutrons are captured by surrounding nuclei, and then decay to a proton by emitting an electron and an antineutrino. Each captured neutron will cause the atomic number of that nucleus to go up by one upon its decay.
 
  • #23
Ken G
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And note that excellent entry is still quite vague about the reason for this "limit" that the core reaches. The standard but incorrect answer is that the limit is some new kind of pressure that appears when the gas goes degenerate. Actually, "degeneracy pressure" is a perfectly mundane form of gas pressure, its arrival merely signifies a situation where the gas (now a gas of free neutrons) can no longer lose heat and thus goes adiabatic, and if it is nonrelativistic, adiabatic compression always causes this mundane gas pressure to rise faster than the gravity does. The "limit" is thus a limit on how much heat can be lost from the core, which is only indirectly a limit on the force scale. But if the neutrons go relativistic, they are not stabilized against compression even in the adiabatic limit, so that's what leads to black hole formation.
 
  • #24
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[ QUOTE="Ken G, post: 5139168, member: 116697"]That is certainly a standard way to describe the situation, but I am pointing out the potential for that language to lead to misconceptions. In strict terms, the only gross macroscopic effect of degeneracy is the inhibition of heat loss, and as such it does not "cause" an outward force. (It also inhibits internal collisions, so it conducts heat very efficiently, but that just redistributes excess heat, most of the internal kinetic energy is still insulated against any heat loss.)

(snipped paragraph).

So what happens in bigger stars? The neutrons go relativistic. It turns out that relativistic kinetic energy is never good at producing pressure that can resist gravitational contraction, because then gravitational contraction only supplies an equal amount of energy as needed for the increasing pressure to keep pace with the increasing gravity (so continues to lag behind if out of balance), rather than providing twice that amount as happens in nonrelativistic gas (so causes the pressure to eventually rise up and exceed gravity, as happens in a core bounce). That fact has nothing to do with degeneracy, degeneracy only tells you if heat loss will be stopped before the gas goes relativistic. If the gas has already gone relativistic, degeneracy is of no importance.[/QUOTE]

Well, your are correct. Thats why I left outward force in quotes, though. But gravity is countered, and if not for the degeneracy, it wouldn't be. And I might assert(insist, demand, have a hissy fit over) that the formation of say, a neutron star is rather macroscopic.
 
  • #25
Ken G
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But gravity is countered, and if not for the degeneracy, it wouldn't be.
That kind of depends on what you mean. If you took a white dwarf, and instantly tagged every electron such that they were no longer indistinguishable and did not obey the Pauli exclusion principle (let's not worry about the impossibility of actually doing that!), you might think that the star would instantly lose its support, and be crushed by gravity, if you think that degeneracy is responsible for the pressure. But this is just the misconception I was alluding to, that isn't true-- the star will still remain quite close to force balance, all that will happen is it will be able to lose heat. So it will start losing heat, and will start contracting, but the contraction will be gradual on the free-fall timescale because the heat transport timescale is still much longer than that. Indeed, over a single free-fall timescale, you might not notice much at all about the white dwarf, when you turn off its degeneracy. I'm not sayinig you claimed otherwise, merely that it is an important clarification to make because we often see language that might be interpreted differently.
And I might assert(insist, demand, have a hissy fit over) that the formation of say, a neutron star is rather macroscopic.
I can agree it is macroscopic, but I'm not sure what significance you are implying. It is also quantum mechanical, so we have a granddaddy of an example of a phenomenon that is both macroscopic and quantum mechanical (even better is white dwarfs).
 

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