He and student Kurt Liffman computed a pathbreaking history of survival rates of refractory stardust in the interstellar medium after its ejection from stars; and with student Mark D . Leising computed a propagation model of positron annihilation lines emitted from nova explosions and of the angular distribution of gamma ray lines from radioactive 26 Al in the galaxy.
32.
For example, consider electron & ndash; positron annihilation, in which the rest mass of individual particles is destroyed, but the inertia equivalent of the system of the two particles ( its invariant mass ) remains ( since all energy is associated with mass ), and this inertia and invariant mass is carried off by photons which individually are massless, but as a system retain their mass.
