Starship Asterisk*

Recycling Cassiopeia A

Explanation: Massive stars in our Milky Way Galaxy live spectacular lives. Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation can begin anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant would have been first seen in planet Earth's sky about 350 years ago, although it took that light about 11,000 years to reach us. This false-color Chandra X-ray Observatory image shows the still hot filaments and knots in the Cassiopeia A remnant. High-energy emission from specific elements has been color coded, silicon in red, sulfur in yellow, calcium in green and iron in purple, to help astronomers explore the recycling of our galaxy's star stuff - Still expanding, the blast wave is seen as the blue outer ring. The sharp X-ray image, spans about 30 light-years at the estimated distance of Cassiopeia A. The bright speck near the center is a neutron star, the incredibly dense, collapsed remains of the massive stellar core.

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Thank you for the outstanding image and informative post. If I understand correctly, the first few sentences are a brief description of a stellar life cycle; if that's the case, shouldn't the "few million years" be a few billion?

Nice Xray image.... but it looks like it is in PAIN, and for a good reason...poor thing...

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Boomer12k wrote:Nice Xray image.... but it looks like it is in PAIN, and for a good reason...poor thing...

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Yes! I agree! Agony!

Please help me understand why it is hot after all this time, is there still fusion going on in the remnants?

Guest wrote:Thank you for the outstanding image and informative post. If I understand correctly, the first few sentences are a brief description of a stellar life cycle; if that's the case, shouldn't the "few million years" be a few billion?

Nope, [super] massive stars burn fast, bright, and die young. Millions of years is correct. For example the massive star Eta Carinae is estimated to be only 3 million years old, and it is already in its death throe. It has maybe a few ten thousands of years left.

Guest wrote:Thank you for the outstanding image and informative post. If I understand correctly, the first few sentences are a brief description of a stellar life cycle; if that's the case, shouldn't the "few million years" be a few billion?

The more massive the star is, the hotter its core becomes, and so it will burn through its light elements much faster than stars like the Sun. Very massive stars do have relatively short life cycles.

Bruce

Winstond wrote:Please help me understand why it is hot after all this time, is there still fusion going on in the remnants?

No, fusion wouldn't still be going on, but some fission would be. But the main reason it's so hot now is because it was so much hotter when the star blew up, and because the vacuum of space is a good insulator. Things cool off slower in space than they would inside a planet's atmosphere.

Bruce

BDanielMayfield wrote:

Winstond wrote:
Please help me understand why it is hot after all this time, is there still fusion going on in the remnants?

No, fusion wouldn't still be going on, but some fission would be. But the main reason it's so hot now is because it was so much hotter when the star blew up, and because the vacuum of space is a good insulator. Things cool off slower in space than they would inside a planet's atmosphere.

https://en.wikipedia.org/wiki/Cassiopeia_A wrote:
<<In 2013, astronomers detected phosphorus in Cassiopeia A, which confirmed that this element is produced in supernovae through supernova nucleosynthesis. The phosphorus-to-iron ratio in material from the supernova remnant could be up to 100 times higher than in the Milky Way in general.>>

A little fusion & a little fission is still taking place.

But primarily the initial expansion kinetic energy has continued to slow from ~30,000 km/s to ~5,000 km/s over the last ~350 years as it has collided supersonically with the highly rarefied interstellar medium. There are also "high velocity outlying eject knots moving with transverse velocities of 5,500−14,500 km/s with the highest speeds occurring in two nearly opposing jets."

neufer wrote:

BDanielMayfield wrote:

Winstond wrote:
Please help me understand why it is hot after all this time, is there still fusion going on in the remnants?

No, fusion wouldn't still be going on, but some fission would be. But the main reason it's so hot now is because it was so much hotter when the star blew up, and because the vacuum of space is a good insulator. Things cool off slower in space than they would inside a planet's atmosphere.

https://en.wikipedia.org/wiki/Cassiopeia_A wrote:
<<In 2013, astronomers detected phosphorus in Cassiopeia A, which confirmed that this element is produced in supernovae through supernova nucleosynthesis. The phosphorus-to-iron ratio in material from the supernova remnant could be up to 100 times higher than in the Milky Way in general.>>

A little fusion & a little fission is still taking place.

But primarily the initial expansion kinetic energy has continued to slow from ~30,000 km/s to ~5,000 km/s over the last ~350 years as it has collided supersonically with the highly rarefied interstellar medium. There are also "high velocity outlying eject knots moving with transverse velocities of 5,500−14,500 km/s with the highest speeds occurring in two nearly opposing jets."

Yeah. After I made that post I remembered that kinetic energy would also supply a continuing heat source, but that would be primarily in the blue blast front as shown in today's APOD.

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.

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.

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!

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?

Bruce

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.

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 cores 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. Anyway, that's my opinion until convincing arguments convince me otherwise.

Bruce

Someone called Robert Fesen loves Cassiopeia A!

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.

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

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?

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.

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.

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

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.

Well, technically, as long as your display is warmer than absolute zero there is a finite chance of it emitting a photon of any arbitrary energy. Doing so under the control of your computer, however... not so much.

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

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

Of course, if we were inside something like that, we wouldn't even notice it without sensitive instruments.

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.>>