Thursday, August 2, 2012

Clusters, Galaxies, Supernovae, and Hypernovae

I taught Astronomy for the first time this last summer at Carl Sandburg College.  It was an interesting experience, being as I had taught physics quite a bit, but I'd never really even taken an Astronomy course.  During the few weeks prior to the class I was racing through the textbook as fast as I could.

When I came to the part about globular clusters and open clusters, I started to fit some things together.


The basic idea here is that a similar event might have drastically different results depending on the surrounding density.  In these videos I'm imagining something like a Type II supernova occurring in three different environments--high density, medium density, and low density.  In the high density case, the end result is a full-blown galaxy.  In the medium density case, the end result is a globular cluster.  In the low density case, the result is an open cluster.

We could go lower-density still, to the point where we just get nebula--gas and dust clouds out of the supernova explosion, or we could go to the other extreme, a hypernova.

In an ordinary Type II supernova "The enormous inward gravitational pull of matter ensures catastrophe...  Gravity overwhelms the pressure of the hot gas, and the str implodes, falling in on itself.  The core temperature rises to nearly 10 billion Kelvin.  At these temperatures individual photons are energetic enough to split iron into lighter nuclei and then break those lighter nuclei apart until only protons and neutrons remain.  This process is known as photodisintegration.  In less than a second, the collapsing core undoes all the effects of nuclear fusion that occurred during the previous 10 million years.  But to split iron and lighter nuclei into smaller pieces requires a lot of energy.  After all, this splitting is the opposite of the fusion reaction that generated the star's energy during earlier times.  The process thus absorbs some of the core's heat energy, reducing the pressure and accelerating the collapse....  There is nothing to prevent the collapse from continuing all the way to the point at which the neutrons themselves come into contact with each other, at the incredible density of 1015 kg/m3... by the time the collapse is actually halted, the core overshoots its point of equilibrium and may reach a density as high as 1015 kg/mbefore beginning to reexpand.  Like a fast-moving ball hitting a brick wall, the core becomes compressed, stops, then rebounds with a vengeance."  (From Astronomy; A beginner's Guide to the Universe, Chaisson McMillan)

Now imagine an environment where the infalling matter is so dense that this photodisintegration/compaction/reexpansion process repeats itself in a region outside the core.


  1. I was watching CNN at my aunt's house today, 8/15/2012, and there was someone on there discussing a supermassive galaxy-cluster... But what he was describing was what might look like a single galaxy with something like 100 trillion stars. I think it's a single galaxy on the scale of a galaxy cluster. It is the perturbation caused by a hypernova happening in the very-very early universe. Is this an energetic enough perturbation to cause what I called the "secondary bang" in my 8/14 blog? Was there a similar formation right here billions of years ago, before it separated out into our local group of galaxies? I wish there were a way to look up the stories that were reported on CNN today on the web, so I could see more exactly who this astronomer was, and more exact information about the formation.

    1. Here it is: