dougettinger wrote:The shock wave does slow down as it moves away from the supernova and it does change densities in the interacting gases. Do the materials from the supernova slow down, too, due to some drag function of the shock front ?
You are still confusing the material moving away from the supernova (which may itself contain shock fronts, but does not have to) with the shock fronts generated in the IMC when fast moving material strikes it. Shock fronts can move either faster or slower than the individual components that make it up. For instance, spiral arms of galaxies are a type of density front, where the stars that make them up are moving faster than the overall spiral structure.
doug wrote:I am curious to know what amount of density change occurs and what affect different velocity differentials have on the overall outcome ?
I have no idea. I would assume only a very small density gradient is required to start a regional collapse of material. And I doubt that velocity plays much role.
doug wrote:I knew the marble was an example and a good one at that. You are now admitting there will be a full range of sizes of material agglomerations that can include planet-sized. Of course, starting with planet-sized agglomerations can make computer modeling a whole lot easier.
Not at all. As far as I know, the models ignore anything larger than gas and dust, because it represents such a small percentage of the total mass that it is insignificant to the process. Even a tiny density variation in a region of dust extending a light year creates a gravitational field gradient orders of magnitude larger than a planet.
doug wrote:You have introduced something called the "power-law". Is this power law still dealing with Newton's laws of motion and gravity?
A power-law describes some sort of scaling relationship. In this case, it would describe the percentage of mass as a function of the particle size. For example, 90% of the mass is made up of gas; 90% of the remaining mass is made up of dust grains smaller than 1 micrometer; 90% of the remaining mass is made up of dust grains smaller than 1mm, and so forth (the numbers are just examples). A power-law like this might tell you that only one ten-billionth of the total mass is made up of particles larger than 1km.
I work with this type of law all the time in my meteor research. A key component of the work is counting the number of meteors of different sizes in order to define the specific coefficients of the applicable power-law. This allows organizations like NASA and ESA to accurately estimate the probability that a particle of a certain size will impact a given space asset, and therefore to rationally determine how much to shield different spacecraft.
doug wrote:I still am questioning how these tenusous gases and dust can generate a marble size or planet-size agglomeration of matter.
Again, I'd ask you how they can fail to do so, unless you assume there is a repulsive force that can overcome gravitational attraction.
doug wrote:For these time scales what was the initial and final masses of the agglomerations ?
I don't know. There are lots of papers about this stuff, and with a bit of research you could track some down. I think the status of the work at this point is that the models demonstrate the physicality of stellar formation by accretion in IMCs, but there are still key elements missing, since the models fail to explain (or poorly explain) a large percentage of observed star systems. Most researchers would probably say that the theories are on the right track and roughly describe what is happening, but need a lot of work still. The important point for the discussion we're having, at this level, is that there appears nothing in the slightest bit unphysical about density fluctuations in IMCs seeding regions of accretion that can become stars. It's not the complete picture, but it's a good first approximation of reality.
doug wrote:Materials in the IMC come from the dispersal of nova and supernova remnants. Once these remnants become part of a IMC they have lost there plasma characteristics, cooled , condensed, and formed atomic particles. Then the IMC has no electromagnetic properties. This is my assumption.
I wouldn't say it has none, but I don't think there's much evidence to suggest that electromagnetic properties play a significant role in the dynamics of cool molecular clouds.
[quote="dougettinger"]The shock wave does slow down as it moves away from the supernova and it does change densities in the interacting gases. Do the materials from the supernova slow down, too, due to some drag function of the shock front ?[/quote]
You are still confusing the material moving away from the supernova (which may itself contain shock fronts, but does not have to) with the shock fronts generated in the IMC when fast moving material strikes it. Shock fronts can move either faster or slower than the individual components that make it up. For instance, spiral arms of galaxies are a type of density front, where the stars that make them up are moving faster than the overall spiral structure.
[quote="doug"]I am curious to know what amount of density change occurs and what affect different velocity differentials have on the overall outcome ?[/quote]
I have no idea. I would assume only a very small density gradient is required to start a regional collapse of material. And I doubt that velocity plays much role.
[quote="doug"]I knew the marble was an example and a good one at that. You are now admitting there will be a full range of sizes of material agglomerations that can include planet-sized. Of course, starting with planet-sized agglomerations can make computer modeling a whole lot easier.[/quote]
Not at all. As far as I know, the models ignore anything larger than gas and dust, because it represents such a small percentage of the total mass that it is insignificant to the process. Even a tiny density variation in a region of dust extending a light year creates a gravitational field gradient orders of magnitude larger than a planet.
[quote="doug"]You have introduced something called the "power-law". Is this power law still dealing with Newton's laws of motion and gravity?[/quote]
A power-law describes some sort of scaling relationship. In this case, it would describe the percentage of mass as a function of the particle size. For example, 90% of the mass is made up of gas; 90% of the remaining mass is made up of dust grains smaller than 1 micrometer; 90% of the remaining mass is made up of dust grains smaller than 1mm, and so forth (the numbers are just examples). A power-law like this might tell you that only one ten-billionth of the total mass is made up of particles larger than 1km.
I work with this type of law all the time in my meteor research. A key component of the work is counting the number of meteors of different sizes in order to define the specific coefficients of the applicable power-law. This allows organizations like NASA and ESA to accurately estimate the probability that a particle of a certain size will impact a given space asset, and therefore to rationally determine how much to shield different spacecraft.
[quote="doug"]I still am questioning how these tenusous gases and dust can generate a marble size or planet-size agglomeration of matter.[/quote]
Again, I'd ask you how they can fail to do so, unless you assume there is a repulsive force that can overcome gravitational attraction.
[quote="doug"]For these time scales what was the initial and final masses of the agglomerations ?[/quote]
I don't know. There are lots of papers about this stuff, and with a bit of research you could track some down. I think the status of the work at this point is that the models demonstrate the physicality of stellar formation by accretion in IMCs, but there are still key elements missing, since the models fail to explain (or poorly explain) a large percentage of observed star systems. Most researchers would probably say that the theories are on the right track and roughly describe what is happening, but need a lot of work still. The important point for the discussion we're having, at this level, is that there appears nothing in the slightest bit unphysical about density fluctuations in IMCs seeding regions of accretion that can become stars. It's not the complete picture, but it's a good first approximation of reality.
[quote="doug"]Materials in the IMC come from the dispersal of nova and supernova remnants. Once these remnants become part of a IMC they have lost there plasma characteristics, cooled , condensed, and formed atomic particles. Then the IMC has no electromagnetic properties. This is my assumption.[/quote]
I wouldn't say it has none, but I don't think there's much evidence to suggest that electromagnetic properties play a significant role in the dynamics of cool molecular clouds.