APOD: Recycling Cassiopeia A (2017 Dec 28)

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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by neufer » Thu Dec 28, 2017 8:14 pm

BDanielMayfield wrote:
neufer wrote:
A little fusion & a little fission is still taking place.
It's interesting about the continuing fusion producing phosphorus Art. I wouldn't have thought the conditions would be extreme enough this long after the SN blast. Must read more about it...After reading the links you quoted I remain unconvinced about fusion still being able to proceed after 350 years of cooling and dispersion in Cas A. What is the P producing reaction that is allegedly still ongoing?
OK, so no fusion: The protons lack the energy to pass the coulomb barrier and the neutrons have a half live of just 10.2 minutes.

However, before the neutrons decay away over the first few hours they can interact with stable silicon isotopes to produce unstable silicon31 which then beta decays into stable phosphorus31. https://www.youtube.com/watch?v=pxrPaNDvaQE
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by BDanielMayfield » Fri Dec 29, 2017 6:41 am

Chris Peterson wrote: What happens to the velocity of particles that collide at relative speeds too low to result in fusion?
The velocities of the two particles are changed while total momentum is conserved. In other words, the particles bounce/deflect off each other.

Edited to add deflection, because very often the positively charged nucleii would never actually even contact each other.
Last edited by BDanielMayfield on Fri Dec 29, 2017 7:07 am, edited 1 time in total.

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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by BDanielMayfield » Fri Dec 29, 2017 6:52 am

neufer wrote:
BDanielMayfield wrote:
neufer wrote:
A little fusion & a little fission is still taking place.
It's interesting about the continuing fusion producing phosphorus Art. I wouldn't have thought the conditions would be extreme enough this long after the SN blast. Must read more about it...After reading the links you quoted I remain unconvinced about fusion still being able to proceed after 350 years of cooling and dispersion in Cas A. What is the P producing reaction that is allegedly still ongoing?
OK, so no fusion: The protons lack the energy to pass the coulomb barrier and the neutrons have a half live of just 10.2 minutes.

However, before the neutrons decay away over the first few hours they can interact with stable silicon isotopes to produce unstable silicon31 which then beta decays into stable phosphorus31.
Thanks Art, and very informative post.

Just as cold fusion isn't possible, warm fusion isn't possible either.
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by Ann » Fri Dec 29, 2017 8:44 am

BDanielMayfield wrote:
Chris Peterson wrote:
APOD Robot wrote:This false-color Chandra X-ray Observatory image...
I'm certainly glad that the decision was made to apply false colors. Those hard x-rays coming out of my screen would have been a bitch!
Good one. :lol2:
Even I, the hater of false color, must agree! :lol2:

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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by Chris Peterson » Fri Dec 29, 2017 2:32 pm

BDanielMayfield wrote:
Chris Peterson wrote: What happens to the velocity of particles that collide at relative speeds too low to result in fusion?
The velocities of the two particles are changed while total momentum is conserved. In other words, the particles bounce/deflect off each other.
Exactly. So what does that suggest about subsequent collisions those particles experience?
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by neufer » Fri Dec 29, 2017 2:56 pm

Ann wrote:
BDanielMayfield wrote:
Chris Peterson wrote:
I'm certainly glad that the decision was made to apply false colors.
Those hard x-rays coming out of my screen would have been a bitch!
Good one. :lol2:
Even I, the hater of false color, must agree! :lol2:
http://asterisk.apod.com/viewtopic.php? ... 83#p278348
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by BDanielMayfield » Fri Dec 29, 2017 3:15 pm

Chris Peterson wrote:
BDanielMayfield wrote:
Chris Peterson wrote: What happens to the velocity of particles that collide at relative speeds too low to result in fusion?
The velocities of the two particles are changed while total momentum is conserved. In other words, the particles bounce/deflect off each other.
Exactly. So what does that suggest about subsequent collisions those particles experience?
It suggests to me that, unless more energy is added, the strong trend over time is that the likelihood of any subsequent collisions causing a fusion becomes nil.

My point is not that fusion doesn't occur for a time post SN blast, but that as the debris cool and disperse the point is reached where fusion peters out completely. I contend that the time for this post blast fusion would have to be < , and maybe even << 350 years.

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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by Chris Peterson » Fri Dec 29, 2017 3:22 pm

BDanielMayfield wrote:
Chris Peterson wrote:
BDanielMayfield wrote: The velocities of the two particles are changed while total momentum is conserved. In other words, the particles bounce/deflect off each other.
Exactly. So what does that suggest about subsequent collisions those particles experience?
It suggests to me that, unless more energy is added, the strong trend over time is that the likelihood of any subsequent collisions causing a fusion becomes nil.

My point is not that fusion doesn't occur for a time post SN blast, but that as the debris cool and disperse the point is reached where fusion peters out completely. I contend that the time for this post blast fusion would have to be < , and maybe even << 350 years.
How do you come to that conclusion? What matters is the temperature, and we know that after that length of time the mix is still very hot (why wouldn't it be- there are no efficient cooling mechanisms in place, especially as the debris becomes more dispersed). My point is that we don't have everything moving out radially- collisions between particles result in a wide range of velocities, which means that we still have collisions between particles with high relative speeds, and therefore the possibility of fusion. Certainly the fusion rate is low, but the total mass is high, which means that fusion in such places can be a significant source of trace elements. Heck, fusion in open, interstellar space caused by cosmic rays hitting free particles is a known contributor to the formation of certain elements.
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by neufer » Fri Dec 29, 2017 4:14 pm

Chris Peterson wrote:
BDanielMayfield wrote:
My point is not that fusion doesn't occur for a time post SN blast, but that as the debris cool and disperse the point is reached where fusion peters out completely. I contend that the time for this post blast fusion would have to be < , and maybe even << 350 years.
How do you come to that conclusion? What matters is the temperature, and we know that after that length of time the mix is still very hot (why wouldn't it be- there are no efficient cooling mechanisms in place, especially as the debris becomes more dispersed). My point is that we don't have everything moving out radially- collisions between particles result in a wide range of velocities, which means that we still have collisions between particles with high relative speeds, and therefore the possibility of fusion. Certainly the fusion rate is low, but the total mass is high, which means that fusion in such places can be a significant source of trace elements. Heck, fusion in open, interstellar space caused by cosmic rays hitting free particles is a known contributor to the formation of certain elements.
  • Any relativistic cosmic rays coming out of a supernova left the area very early in the process.
https://en.wikipedia.org/wiki/Sun#Core wrote:
<<The core of the Sun extends from the center to about 20–25% of the solar radius. It has a density of up to 150 g/cm3 and a temperature of close to 15.7 million kelvins (K). Theoretical models of the Sun's interior indicate a power density of approximately 276.5 W/m3, a value that more nearly approximates that of reptile metabolism or a compost pile than of a thermonuclear bomb.>>
Core nuclear fusion is so slow that the Sun "burns" for 10 billion years!

The low solar core "metabolism" is due to the temperature x density being so low
that quantum tunneling is required to overcome electrostatic repulsion.
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by Chris Peterson » Fri Dec 29, 2017 4:30 pm

neufer wrote:Any relativistic cosmic rays coming out of a supernova left the area very early in the process.
Yeah. Your point? My comment is unrelated to what's happening around a recent supernova.
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by neufer » Fri Dec 29, 2017 5:49 pm

Chris Peterson wrote:
neufer wrote:
Any relativistic cosmic rays coming out of a supernova left the area very early in the process.
Yeah. Your point? My comment is unrelated to what's happening around a recent supernova.
Bruce corrected my initial error.

Any supernova remnant older than a few hours has negligible fusion taking place because:
  • 1) the temperature is too low
    2) all cosmic rays have dispersed
    3) all neutrons have decayed and
    4) the density is too low (even in the shock layers).
So what is your point, Chris?
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by Chris Peterson » Fri Dec 29, 2017 5:57 pm

neufer wrote:
Chris Peterson wrote:
neufer wrote:
Any relativistic cosmic rays coming out of a supernova left the area very early in the process.
Yeah. Your point? My comment is unrelated to what's happening around a recent supernova.
Bruce corrected my initial error.

Any supernova remnant older than a few hours has negligible fusion taking place because:
  • 1) the temperature is too low
    2) all cosmic rays have dispersed
    3) all neutrons have decayed and
    4) the density is too low (even in the shock layers).
So what is your point, Chris?
My point was that I didn't understand your point.

That said, I disagree. The temperatures are high enough that fusion must be occurring. Define "neglible". Certainly, the density is not too low, given that fusion occurs in deep interstellar and intergalactic space, where particle densities are lower by many orders of magnitude.

A very low fusion rate, times a very large total mass, can still result in significant element formation.
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by BDanielMayfield » Fri Dec 29, 2017 6:47 pm

neufer wrote:
  • Any relativistic cosmic rays coming out of a supernova left the area very early in the process.
https://en.wikipedia.org/wiki/Sun#Core wrote: <<The core of the Sun extends from the center to about 20–25% of the solar radius. It has a density of up to 150 g/cm3 and a temperature of close to 15.7 million kelvins (K). Theoretical models of the Sun's interior indicate a power density of approximately 276.5 W/m3, a value that more nearly approximates that of reptile metabolism or a compost pile than of a thermonuclear bomb.>>
Core nuclear fusion is so slow that the Sun "burns" for 10 billion years!

The low solar core "metabolism" is due to the temperature x density being so low
that quantum tunneling is required to overcome electrostatic repulsion.
An excellent argument Art, except that what we're taking about here are conditions with much more extreme starting temps and densities than in the Sun's core. Quantum tunneling, whereby a few fusion reactions can occur below the average fusion collisional energy threshold for any given reaction, would also be an important contributor for the class of interstellar reactions that Chris is suggesting.
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by BDanielMayfield » Fri Dec 29, 2017 7:19 pm

Chris Peterson wrote:
neufer wrote:
Chris Peterson wrote: Yeah. Your point? My comment is unrelated to what's happening around a recent supernova.
Bruce corrected my initial error.

Any supernova remnant older than a few hours has negligible fusion taking place because:
  • 1) the temperature is too low
    2) all cosmic rays have dispersed
    3) all neutrons have decayed and
    4) the density is too low (even in the shock layers).
So what is your point, Chris?
My point was that I didn't understand your point.

That said, I disagree. The temperatures are high enough that fusion must be occurring. Define "neglible". Certainly, the density is not too low, given that fusion occurs in deep interstellar and intergalactic space, where particle densities are lower by many orders of magnitude.

A very low fusion rate, times a very large total mass, can still result in significant element formation.
Art: On your point 3, it's very true that the initial flux of neutrons in the blast would have either decayed or have been absorbed by other nuclei. However, wouldn't there have to be a continuing source of fresh neutrons from decaying isotopes :?: (Hits from such newly liberated neutrons on Si would help explain the over abundance of P in Cas A.)

Chris: What elements are actually fused in these alleged interstellar reactions? I've heard of spalation reactions whereby light elements like B and Be are produced, but those reactions spilt nuclei instead of fusing them.

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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by neufer » Fri Dec 29, 2017 9:27 pm

BDanielMayfield wrote:
neufer wrote:
Bruce corrected my initial error.

Any supernova remnant older than a few hours has negligible fusion taking place because:
  • 1) the temperature is too low
    2) all cosmic rays have dispersed
    3) all neutrons have decayed and
    4) the density is too low (even in the shock layers).
Art: On your point 3, it's very true that the initial flux of neutrons in the blast would have either decayed or have been absorbed by other nuclei. However, wouldn't there have to be a continuing source of fresh neutrons from decaying isotopes :?: (Hits from such newly liberated neutrons on Si would help explain the over abundance of P in Cas A.)
Normal radioactive decays usually involve charged alpha particles or beta particles.

Many light neutron rich elements (e.g., 5He, 7He, 9He, 10He, etc.) that do decay by emitting neutrons will certainly be generated in the first hour. However, these decay almost immediately (~10-21 seconds) and so cannot act as neutron lifeboats.
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by neufer » Fri Dec 29, 2017 9:40 pm

BDanielMayfield wrote:
neufer wrote:
  • Any relativistic cosmic rays coming out of a supernova left the area very early in the process.
https://en.wikipedia.org/wiki/Sun#Core wrote:
<<The core of the Sun extends from the center to about 20–25% of the solar radius. It has a density of up to 150 g/cm3 and a temperature of close to 15.7 million kelvins (K). Theoretical models of the Sun's interior indicate a power density of approximately 276.5 W/m3, a value that more nearly approximates that of reptile metabolism or a compost pile than of a thermonuclear bomb.>>
Core nuclear fusion is so slow that the Sun "burns" for 10 billion years!

The low solar core "metabolism" is due to the temperature x density being so low
that quantum tunneling is required to overcome electrostatic repulsion.
An excellent argument Art, except that what we're taking about here are conditions with much more extreme starting temps and densities than in the Sun's core. Quantum tunneling, whereby a few fusion reactions can occur below the average fusion collisional energy threshold for any given reaction, would also be an important contributor for the class of interstellar reactions that Chris is suggesting.
With initial radial velocities of 0.1c the densities after the first few hours should be much less that the Sun's core density!

H-bomb fuel material (i.e., tritium, deuterium or lithium deuteride) might still fuse at the shock boundary but that would be about it.
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Re: APOD: Recycling Cassiopeia A (2017 Dec 28)

Post by BDanielMayfield » Fri Dec 29, 2017 11:42 pm

You've defended the case for no or vanishingly little long term post SN fusion very well Art.

Chris, I understood the points you were making about some particle collisions having sufficient energy for fusions in SN remnant material. You're right about the temps remaining high for an extended time, but Art is right about the density being too low. The problem is that the reaction cross sections are so small that the perfectly aligned bullseye collisions required for fusion to occur simply can't happen with any appreciable frequency.

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