APOD and General Astronomy Discussion Forum
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They're not expanding because they're hot. They're moving away from the center of mass of the star because the explosion has propelled them outwards at a velocity greater than the escape velocity of the star.THX1138 wrote:... How is it that; say when a star explodes, the star parts and gasses stay so hot as they expand into the universe.
Radiative heat transfer is not very efficient. You have several solar masses of material heated to may thousands of kelvins. It takes a long time to lose that energy via the emission of photons.THX1138 wrote:What with the cosmic microwave temperature being somewhere around -270.45 Celsius and interstellar space being i don't know what, but surely cold.
How is it that; say when a star explodes, the star parts and gasses stay so hot as they expand into the universe.
Chris Peterson wrote:Radiative heat transfer is not very efficient. You have several solar masses of material heated to may thousands of kelvins. It takes a long time to lose that energy via the emission of photons.THX1138 wrote:
How is it that; say when a star explodes, the star parts and gasses stay so hot as they expand into the universe.
) taking thousands of years to lose that energy via the emission of relativistic cosmic rays. Eventually one is left with a bubble in the interstellar medium at a typical warm temperature of ~10,000 K.https://en.wikipedia.org/wiki/Supernova_remnant wrote:
<<[Supernova explosions expel] much or all of the stellar material with velocities as much as 10% the speed of light, that is, about 30,000 km/s. These ejecta are highly supersonic: assuming a typical temperature of the interstellar medium of 10,000 K, the Mach number can initially be > 1000. Therefore, a strong shock wave forms ahead of the ejecta, that heats the upstream plasma up to temperatures well above millions of K. The shock continuously slows down over time as it sweeps up the ambient medium, but it can expand over hundreds or thousands of years and over tens of parsecs before its speed falls below the local sound speed.
Supernova remnants are considered the major source of galactic cosmic rays. The connection between cosmic rays and supernovas was first suggested by Walter Baade and Fritz Zwicky in 1934. Vitaly Ginzburg and Sergei Syrovatskii in 1964 remarked that if the efficiency of cosmic ray acceleration in supernova remnants is about 10 percent, the cosmic ray losses of the Milky Way are compensated. This hypothesis is supported by a specific mechanism called "shock wave acceleration" based on Enrico Fermi's ideas, which is still under development.
Indeed, Enrico Fermi proposed in 1949 a model for the acceleration of cosmic rays through particle collisions with magnetic clouds in the interstellar medium. This process, known as the "Second Order Fermi Mechanism", increases particle energy during head-on collisions, resulting in a steady gain in energy. A later model to produce Fermi Acceleration was generated by a powerful shock front moving through space. Particles that repeatedly cross the front of the shock can gain significant increases in energy. This became known as the "First Order Fermi Mechanism".
Supernova remnants can provide the energetic shock fronts required to generate ultra-high energy cosmic rays. Observation of the SN 1006 remnant in the X-ray has shown synchrotron emission consistent with it being a source of cosmic rays. However, ...it is still unclear whether supernova remnants accelerate cosmic rays up to PeV energies. The future telescope CTA will help to answer this question.>>
Excellent observation!neufer wrote:Chris Peterson wrote:Radiative heat transfer is not very efficient. You have several solar masses of material heated to may thousands of kelvins. It takes a long time to lose that energy via the emission of photons.THX1138 wrote:
How is it that; say when a star explodes, the star parts and gasses stay so hot as they expand into the universe.
- You have at least one solar mass of material at "velocities as much as 10% the speed of light" (i.e., comparable to trillions of kelvins :!: ) taking thousands of years to lose that energy via the emission of relativistic cosmic rays. Eventually one is left with a bubble in the interstellar medium at a typical warm temperature of ~10,000 K.
Yes, but it's a lot more intuitive that a molten region insulated deep in a planetoid will cool slowly than it is an extremely tenuous gas will.Fred the Cat wrote:Meteorites sure tell that tale. http://asterisk.apod.com/viewtopic.php? ... 41#p255473
"Widmanstätten pattern -From the Gibeon meteorite discovered in 1836 in Nambia. This particular alloy (nickel-iron) in this type of pattern is found only in meteorites. According to scientists, the only way that these patterns can form (long crystals of nickel-iron) is when the molten core of a planetoid cools down at one degree every million years."
That thought came to me after I posted. Of course if the planetoid was blasted into smithereens while it was still hot creating the meteorite – would it still have the same Widmanstätten pattern?Chris Peterson wrote:Yes, but it's a lot more intuitive that a molten region insulated deep in a planetoid will cool slowly than it is an extremely tenuous gas will.Fred the Cat wrote:Meteorites sure tell that tale. http://asterisk.apod.com/viewtopic.php? ... 41#p255473
"Widmanstätten pattern -From the Gibeon meteorite discovered in 1836 in Nambia. This particular alloy (nickel-iron) in this type of pattern is found only in meteorites. According to scientists, the only way that these patterns can form (long crystals of nickel-iron) is when the molten core of a planetoid cools down at one degree every million years."
Nope. Not all iron meteorites show Widmanstätten structures. It might be because they have too much nickel (e.g. ataxites), or it might be because the parent body was large enough to result in differentiation, but small enough that it cooled too quickly for the crystals to form. It might also have been metamorphosed by subsequent heating in collisions.Fred the Cat wrote:That thought came to me after I posted. Of course if the planetoid was blasted into smithereens while it was still hot creating the meteorite – would it still have the same Widmanstätten pattern?Chris Peterson wrote:Yes, but it's a lot more intuitive that a molten region insulated deep in a planetoid will cool slowly than it is an extremely tenuous gas will.
No, this slice is in Denver. But it looks a lot like the slice at AMNH since they're parallel slices, adjacent or nearly so.geckzilla wrote:Haha, that's the sucker sitting in the museum here? I got shooed away from the thing because I was touching it. Well, I got shooed away from some very large iron meteorite, anyway. It was just sitting there, begging to be touched...
Supernova ejecta start off with lots of kinetic energy but it is not random (i.e., thermal). The ejecta is constantly sweeping up new material thereby sharing its kinetic energy with interstellar matter as well as generating cosmic rays which rapidly escape into the galaxy. Little of its kinetic energy as released in photons.THX1138 wrote:
Interesting that the ambient medium (of space) can be heated up, ahead of ejecta even,
But that same medium, which can retain heat, cannot dissipate heat very well.
Minus hundreds of degrees for light years in every direction the ejecta can remain hot for thousands of years flying through it
Seems like space ( an or a vacuum in general ) is like the ultimate insulator
If i'm understanding what your saying correctly ?
Had you stumbled upon this concept much earlier, you might have patented the Thermos and made your fortune.THX1138 wrote:Seems like space ( an or a vacuum in general ) is like the ultimate insulator
Radiative transfer from hot black coffee is relatively efficient which explains why Thermos flasks are silvered.Chris Peterson wrote:Had you stumbled upon this concept much earlier, you might have patented the Thermos and made your fortune.THX1138 wrote:
Seems like space ( an or a vacuum in general ) is like the ultimate insulator
A Thermos (formally a Dewar flask) works by nesting a pair of flasks, separated by a vacuum. The structure holding the inner flask to the outer is minimal, so there is very little conductive heat transfer between the two. The vacuum eliminates convective heat transfer. That just leaves radiative transfer, which being inefficient, allows the inner flask contents to remain near its original temperature for a long time.
https://en.wikipedia.org/wiki/James_Dewar wrote:
<<By 1891, [Sir James Dewar (20 September 1842 – 27 March 1923)] had designed and built, at the Royal Institution, machinery which yielded liquid oxygen in industrial quantities, and towards the end of that year, he showed that both liquid oxygen and liquid ozone are strongly attracted by a magnet. About 1892, the idea occurred to him of using vacuum-jacketed vessels for the storage of liquid gases – the Dewar flask (otherwise known as a Thermos or vacuum flask) – the invention for which he became most famous. The vacuum flask was so efficient at keeping heat out, it was found possible to preserve the liquids for comparatively long periods, making examination of their optical properties possible. Dewar did not profit from the widespread adoption of his vacuum flask – he lost a court case against Thermos concerning the patent for his invention. While Dewar was recognised as the inventor, because he did not patent his invention, no way to stop Thermos from using the design was possible.>>
Then Starbucks invented a quasi-magnetic coffee that put a dent in Thermosneufer wrote:https://en.wikipedia.org/wiki/James_Dewar wrote:
<<By 1891, [Sir James Dewar (20 September 1842 – 27 March 1923)] had designed and built, at the Royal Institution, machinery which yielded liquid oxygen in industrial quantities, and towards the end of that year, he showed that both liquid oxygen and liquid ozone are strongly attracted by a magnet. About 1892, the idea occurred to him of using vacuum-jacketed vessels for the storage of liquid gases – the Dewar flask (otherwise known as a Thermos or vacuum flask) – the invention for which he became most famous. The vacuum flask was so efficient at keeping heat out, it was found possible to preserve the liquids for comparatively long periods, making examination of their optical properties possible. Dewar did not profit from the widespread adoption of his vacuum flask – he lost a court case against Thermos concerning the patent for his invention. While Dewar was recognised as the inventor, because he did not patent his invention, no way to stop Thermos from using the design was possible.
