Difference between blast & shock wave

AI Thread Summary
A shock wave is characterized by a gradual change in variables behind it, while a blast wave represents a sharp peak in these changes, often resulting from an energetic explosion. The Sedov-Taylor phase of a supernova remnant (SNR) is identified as a blast wave, indicating that other phases may not share this characteristic. The propagation of both waves is influenced by the mean free path of particles in the medium, which can vary significantly in different environments, such as the vacuum of space. The distinction between a blast wave and a shock wave can be nuanced, as a blast wave can be seen as a specific type of shock wave with concentrated energy at a point. Overall, understanding these differences is crucial for modeling and analyzing phenomena in astrophysics.
Jain_Mor
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Hi guys and gals,

with respect to SNRs (or anything for that matter)

What is the difference between a shock wave and a blast wave?
Is it just that a blast wave is a sharp peak in the change in variables, where as a shock wave has a region behind it in which the variables gradually decrease?

Also read that the Sedov-Taylor or Self-Similar phase of an SNR is a blast wave, does this mean the other phases aren't?

Many thanks in advance, its confusing quite a lot of us.
 
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A blast wave is the initial pulse from an energetic explosion. It is simply a strongly peaked shock wave, so you're on the right track. Propogation of a shock or blast wave is dependent on the mean free path between particles in the medium through which it travels. The mean free path is another way of saying how far apart particles are on average. In the vacuum of space, the mean free path can be quite huge - not unlike an enormous billiard table with only a few balls. The time between collisions can be lengthy. The individual collisions can result in highly energetic photon emissions, but, lack the systemic kinematical effects of shock waves in a denser medium. Plasma effects tend to dominate under these circumstances.
 
Are you speaking relative to SNRs?

Is it possible that a Blast Wave is a Shock Wave whose rarefaction has caught up with the shock front? Thereby giving it a distinct peak?
 
Jain_Mor said:
Is it just that a blast wave is a sharp peak in the change in variables, where as a shock wave has a region behind it in which the variables gradually decrease?

I didn't make that much of a distinction between the two when I did my dissertation, but a blast wave is when you put all of the energy at one point and then you get a very nice easy to solve equation.

Also read that the Sedov-Taylor or Self-Similar phase of an SNR is a blast wave, does this mean the other phases aren't?

Yes. Suppose you have a shock wave that goes out for 0.1 light years. At that point you can model it as a smooth uniform gas in which someone dumped a massive amount of energy at one point, and the numbers work out since the size of the original star is much, much smaller than the area you are looking at. Since the star is a "point" the math becomes really simple.

Now if you try to model the shock wave when it is deep inside the star you can't do that.
 
Jain_Mor said:
Is it possible that a Blast Wave is a Shock Wave whose rarefaction has caught up with the shock front? Thereby giving it a distinct peak?

I don't think that works. There really isn't much in the way of rarefaction.
 
Thanks TwoFish, that's great :)
 
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