Catastrophic Explosions seen through Interstellar Clouds

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I realized that I never wrote about my scientific research (which actually is one of the two sides of my professional life, the other being my functional duties for the European Organization for Astronomical Research). As you may have noticed from my short resumee in the CosmicDiary, I mainly work on Supernovae. Soon there will be a Feature Article on this, so I will not insist too much on this here. Supernovae are the dramatic fate of some stars and are amongst the most energetic phenomena we know. The bottom line is that they eject all (or a large part) of the stellar content into outer space at speeds that reach a significant fraction of the speed of light. In doing this they enrich the surrounding medium with the chemical elements synthesized in their interiors during their “normal” lives and also with the species produced during the explosion itself. Because of the high velocity and mass of the ejected material, they also cause shock waves that sweep the surrounding interstellar medium, causing all sorts of phenomena (escape of material from the galaxy, induced collapse of clouds that would form other stars, and other amenities).

A computer simulated fractal interstellar cloud (credit F. Patat).

A computer simulated fractal interstellar cloud (credit F. Patat).

My work is mostly in the observation of the events, especially when they occur in close-by Galaxies, typically in the Virgo Cluster. You will see one example in the forthcoming Feature Article. Recently I have been interested in the nature of the progenitors of a special sub-class of Supernovae, called Type Ia. While doing this, I stumbled upon an effect which had not been considered before. The interstellar medium appears to be patchy on all scales (technically one would say that it has a fractal structure). Imagine you have a supernova that explodes behind such a patchy sheet of obscuring material. Then you can guess that the luminosity of the SN as seen by a far observer would appear to vary because the light would have to cross regions of the cloud with different opacity. This is similar to what happens when you look at the sun and clouds move in front of it. The only difference is that in the astronomical case is the “sun” that grows bigger and bigger as time goes by. So what, you might ask…

Well, not very much is known about the small structures in the interstellar material and the study of supernovae might shed some light on this. And this is exactly why in the last few months I have been busy with modeling the scenario I just depicted. For doing this, I had to go through the nice exercise of creating clouds with computer simulations. A very nice experience, half way between astrophysics and computer graphics. You can see an example in the above picture (it just came out of my computer, a few minutes ago). Now, the whole game is to calculate how a supernova explosion would look like as seen through clouds like this. Of course, since the cloud structure has a strong random component, this means running a large number of calculations to get, in the end, a statistical estimate. What is usually called Monte-Carlo simulations. As you probably guessed, the name Monte-Carlo comes from the fact that this method makes use of pseudo-random, computer-generated numbers. Similar to the roulette outcome in a Casino…

Curious about the results? Just wait a bit more ;-)

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