General background

Stars form from clouds of molecular gas, the physical properties of which  determine how and what kind of stars form.  Observations of star forming environments reveal that this gas consists of many molecular and ion species (H2, CO, H2O, H3+, H-, and a lot of others), its motions are highly chaotic (turbulent), and detect the presence of a large scale magnetic field.  Star formation processes have now been a target of active research for over 20 years.

A consistent theory of turbulence has not been constructed as yet (this problem is linked with one of the one million dollar problems of the Clay Mathematics Institute), and therefore researchers all over the world rely on computer simulations to understand the underlying physics and processes in star forming environments.

As computer power grows our simulations become more and more realistic, allowing us to include a lot of interesting and potentially vital physics into our models.  Typical astrophysical simulations usually require a supercomputer (a computer, or ensemble of computers, which has more than a single processor (CPU), typically tens or hundreds, sometimes even thousands of CPUs).  Here in Armagh we use an 8 CPU Silicon Graphics Origin 2200 computer, which we call the FORGE, and we have access to the national computational facility -- UKAFF, 128 CPU SGI Origin 3000 supercomputer.

About the movie

This small animation shows the dynamics of hydrogen molecule destruction/reformation in a strongly supersonic turbulent flow.  The fact that the turbulence is supersonic results in *shocks* in the flow. These shocks heat the gas to  high temperatures and dissociate the molecules.  As the turbulence decays, temperatures get lower and molecules start to reform.  We find that reformation happens much faster than it would happen in quiescent, non-turbulent flow.  This simulation demonstrated the importance of a self-consistent treatment of chemistry, physics and dynamics in models of interstellar molecular gas.  Most of the models up to date were ignoring chemistry and were relying on an assumption of isothermality (constant temperature) in their predictions.

We would like to acknowledge UKAFF; FORGE, funded by PPARC JREI scheme, in collaboration with SGI.

Further reading

Armagh links

Article: Pavlovski et al., 2002 Postscript Version
Michael D. Smith Home Page

Other animations

Matthew Bates home page
UKAFF movies page

The simulation and visualisation has been produced by Georgi Pavlovski.

Last Revised: 2003 Arpil 30th WWW contact: webmaster@star.arm.ac.uk

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