Bibcode
DOI
Tenorio-Tagle, G.
Bibliographical reference
Astronomical Journal v.111, p.1641
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4
1996
Citations
169
Refereed citations
131
Description
It is shown here that the ejecta from type II supernovae follow a long
excursion into the galactic environment before they mix with the ISM. We
point to the various changes in temperature, density, and pressure
experienced by the ejecta along their inevitable ride, indicating the
main hydrodynamical events and physical processes taking part in these
changes. The long list of possible ways to disrupt the contact
discontinuity that separates the thermalized ejecta from the swept up
matter, such as cloud crushing, thermal evaporation, hydrodynamical
instabilities, as well as the effects caused by explosions inside
wind-driven shells and by fragmented ejecta, are evaluated. Diffusion is
found to be very effective in the hot coronal phase, causing the ejecta
of correlated supernova explosions to mix with the matter evaporated and
ablated from clouds and the cool outer shell. Once the supernova
activity from a dying OB association comes to an end, the hot matter is
able to cool by radiation. However, given the density and temperature
fluctuations in the hot medium, cooling acts in a differential way. This
is shown to lead to condensation of the metal-rich gas into small
droplets able to fall back and settle onto the disk of the galaxy. The
droplets are likely to become molecular and thus their diffusion into
the cold matter phases (either H I or H2), where molecules
remain bound, is another dispersal agent which together with the motion
of clouds and differential galactic rotation lead to a more homogeneous
distribution of droplets, but not to their mixing with the ISM. True
mixing occurs upon the birth of new generations of massive stars. These
dissociate and disrupt, through photoionization, the heavy element
droplets favoring their almost immediate diffusion into the H II region
volume, finally changing the composition of the ISM.