Question about supernova kinetic energy

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Discussion Overview

The discussion revolves around the kinetic energy associated with a supernova explosion and the subsequent effects of the explosion on the surrounding interstellar medium. Participants explore calculations related to the kinetic energy of the ejecta and the volume of interstellar gas that will be swept up as the ejecta slow down.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant poses a question about calculating the kinetic energy of supernova ejecta and the volume of interstellar gas affected by the explosion.
  • Another participant mentions using the virial theorem to calculate kinetic energy but expresses confusion regarding the swept volume of gas.
  • A different participant argues that the virial theorem may not be appropriate for the scales involved in a supernova event and suggests that kinematical models should be used instead.

Areas of Agreement / Disagreement

Participants have differing views on the appropriateness of the virial theorem for this scenario, indicating a lack of consensus on the best approach to the problem.

Contextual Notes

There is uncertainty regarding the application of the virial theorem in this context, and the assumptions made about the conservation of kinetic energy and the density of the interstellar medium may need further clarification.

lr1
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A9: Supernova Remnants
Consider a supernova explosion in the outer 4M⊙ of a dying star, ejected at a speed of 5000 km/s.
a ◮ What is the kinetic energy of the expanding ejecta?
b ◮ The ejecta are slowed by sweeping up the local interstellar gas. Assuming the density of the interstellar gas
is ig = 2 × 10−19 kg/m3, how large a volume will be swept up by the time the outflow velocity has decreased
to 10 km/s? HINT: Assume the KE of the expansion is conserved.
A10:
 
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hi lr1! welcome to pf! :smile:

(try using the X2 button just above the Reply box :wink:)

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Part a I used virial theorem for kinetic energy 3mv^2 and for part b I used mass= density / volume but am confused with swept volume
 
Virial theorem is only useful on large scales, for a region near a supernova event you still need to use kinematical models.
 

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