However, it is doubtful that clouds of the size and mass observed can survive such an encounter. Alternatively, and much more likely, the objects represent blobs of matter formed in the collapse of the progenitor star and expelled in the subsequent supernova explosion. They will travel largely unaffected through the hot, tenuous, post-shock plasma behind the blast wave and will pass its front at a late stage, when the blast wave has significantly decelerated. However, only very recently the results of two-dimensional hydrodynamical calculations of supernova explosions of massive stars have indicated that supernova explosions are not spherically symmetric. Asymmetries arise from instabilties excited by the passage of the explosion shock wave through the stellar interior.
Convective instabilities form close to the mantle of the nascent neutron star.
Highly heterogeneous clumps of matter so-called 'mushrooms' are formed by these instabilities. The fact that we have observed objects in an SNR which is associated with a neutron star lends support to the presence of these types of instabilities in type Ib or type II supernova explosions of massive stars. Whether we observe the effects which went on in the outer or deep inner layers remains to be seen. This present hypothesis is now being followed by hydrodynamical calculations, which are not terminated at the instance of the explosion but continue to follow the growth and fate of the instabilities throughout the star and the ambient medium. All rights reserved.