Tenorio-Tagle, G.; Rozyczka, M.; Bodenheimer, P. ; The hydrodynamics of superstructures produced by multi-supernova explosions

The hydrodynamics of superstructures produced by multi-supernova explosions

by: Tenorio-Tagle, G.; Rozyczka, M.; Bodenheimer, P.

[ADS: 1990A&A...237..207T, pdf, first author: personal site, second, third]
This is an important historical paper from 1990. The motivation behind this paper goes back several years before this when astronomers were considering the effect that supernovas in OB regions (regions with type O and B stars) would have on the ISM and the general shape and structure of the galactic disk (see references in the introduction for history, VERY important!!! as in I will use these references in my dissertation).

A single supernova will ionize a section of the ISM and will create a small bubble with a well defined boundary and interior and exterior properties. If we consider multiple supernovas then our region begins to become much bigger. At some point the radius of the bubble exceeds the scale height of the galactic disk, thus we are no longer considering a series of blasts in a uniform medium. We now have a stratified medium with a gravitational potential. This changes the properties of the blast region and greatly affects the shape, internal structure and characteristics of the superbubble. There is still a sharp boundary for the region and this transition is termed a "supershell" (Heiles 1979, 1984). The formation of this structure is very important as it is linked to the formation of molecular clouds, which in turn collapse and form stars, thus feeding star formation in a galaxy.

In this paper the authors do 2D simulations of a stratified disk and vary a number of parameters to see how much energy is needed to achieve blow out (i.e. at what point does a bubble become a superbubble). The different parameters tested are summed up in their first table. All units are cgs.

For the density distribution the tried an exponential fall off (exp. 1 and 2), uniform, Gaussian distribution and a composite. Each one is defined in the paper. They also looked at the effect of a hot halo placed on top of the disk and how that changed the blow out.

What is interesting is that the basic structure of the ISM determines the shape and strength of the blow out. Also the velocity of the escaping gas is strongly constrained by the ISM. In the end these superstructures can readily be created by OB complexes and it is assumed that they can persist for many millions of years. The blow out can create a metal rich fountain that when it rains back down on the galaxy will fuel metal rich star formation.

They reference two papers by Mac Low (and others) who were working on this problem at the same time. I may review those papers next. They are: Mac Low and McCray 1988, and Mac Low, McCray and Norman 1989.

Papers Cited:
Heiles, C.; 1979, ApJ, 229, 533-537, 539-544.
Heiles, C.; 1984, ApJS, 55, 585-595.
Mac Low, M.-M. & McCray, R.; 1988 ApJ, 324, 776-785.
Mac Low, M.-M., McCray, R. & Norman, M. L.; 1989, ApJ, 337, 141-154.