Starship Asterisk*

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.

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.)

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.

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.

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?

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.

• 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).

neufer wrote:Any relativistic cosmic rays coming out of a supernova left the area very early in the process.

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.>>

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.

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?

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.

Even I, the hater of false color, must agree!

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.

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.

neufer wrote:

[b][color=#0000FF]The onion-like layers of a massive, evolved star just before core collapse.[/color][/b]

---

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.

Chris Peterson wrote: What happens to the velocity of particles that collide at relative speeds too low to result in fusion?

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?

geckzilla 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!

I'm still looking for a computer screen that can display the cosmic gamut.

• Your computer screen could display actual hard x-rays
  ... but not the soft X-rays (below 10 keV) monitored by Chandra.

https://en.wikipedia.org/wiki/X-ray#Soft_and_hard_X-rays wrote:
<<X-rays with high photon energies (above 5–10 keV, below 0.2–0.1 nm wavelength) are called hard X-rays, while those with lower energy are called soft X-rays. Due to their penetrating ability, hard X-rays are widely used to image the inside of objects, e.g., in medical radiography and airport security. The term X-ray is metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. Since the wavelengths of hard X-rays are similar to the size of atoms they are also useful for determining crystal structures by X-ray crystallography. By contrast, soft X-rays are easily absorbed in air; the attenuation length of 600 eV (~2 nm) X-rays in water is less than 1 micrometer.>>

neufer wrote:

Chris Peterson wrote:

zoomeristic wrote:
Do we know about how far from something this size/energy we need to be to survive the shock, radiation and whatever else? 10s, 100s or thousands of light years?

Outside the unlikely and unfortunate possibility of being in the line of any high energy jets that get produced, just a few light years, perhaps a few tens of light years in the most energetic cases.

https://apod.nasa.gov/apod/ap160425.html

Chris Peterson wrote:

zoomeristic wrote:
Do we know about how far from something this size/energy we need to be to survive the shock, radiation and whatever else? 10s, 100s or thousands of light years?

Outside the unlikely and unfortunate possibility of being in the line of any high energy jets that get produced, just a few light years, perhaps a few tens of light years in the most energetic cases.

geckzilla 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:

I'm still looking for a computer screen that can display the cosmic gamut.

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.

zoomeristic wrote:Do we know about how far from something this size/energy we need to be to survive the shock, radiation and whatever else? 10s, 100s or thousands of light years?

BDanielMayfield wrote:

Chris Peterson wrote:

BDanielMayfield wrote: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.

We have to shift our thinking a bit under these conditions. Fusion requires a collision between two particles. Whether they fuse or not depends upon the speed of the collision. Temperature is a measure of particle speed (kinetic energy). In a SN remnant, you have high heat (particle speed), but very low particle density. So the fusion rate is low, but you still get occasional collisions with consequent fusion.

But, the particle speeds velocities in a SN's expanding shell are not random as they are inside the core's of normally fusing stars; the bulk motion is rapidly away from the SN's center. As you know what matters in fusion reactions is the force of impact and that the impact is within the small reaction cross-section. As the density in the rapidly expanding shell drops the increasingly rare collisions will most often be glancing and therefore wouldn't be forceful enough to induce fusion.