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Theoretical experiment to test the theory of density waves.
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| themohawkninja | Date: Tuesday, 13.08.2013, 20:48 | Message # 1 |
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Space Tourist
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| The current theory (As I understand it) to explain the arms in spiral galaxies is the Denisty Wave Theory. According to this theory, the arms are waves of density that move through the galaxy, which compresses the interstellar medium, and results in the formation of stars, most notably, the large, and very short lived (~10^7 years) type OB stars. These stars live short enough that they should go supernova shortly after the density wave as passed.
Therefor, if a sufficient number of supernova caused from type OB stars can be found, than a computer program could plot the points of all of these on high resolution images of the relevant galaxies, and scientists could then look at where the supernova occurred relative to the spiral arms, and the result would give evidence either for or against the Density Wave Theory.
Any objections to the idea?
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| Gondor2222 | Date: Wednesday, 14.08.2013, 01:30 | Message # 2 |
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| Well current estimates put the supernovae frequency in our galaxy at just a few per century, and about 1/5 of these are due to type Ia supernovae (i.e. they are caused by a different mechanism than the typical OB star supernovae). This gives a theoretical average of about 4 supernovae explosions in our galaxy per century, and a portion of these would likely be masked by the galactic disk. I'd expect the number of type II supernovae observable from Earth to be about 3 per century on average, and at this rate it would take several millenia to have enough data to indicate a general distribution for these supernovae.
That time scale's so large that we'd probably be capable of accurately simulating a galaxy in real time with all the relevant variables long before then.
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| Watsisname | Date: Wednesday, 14.08.2013, 02:24 | Message # 3 |
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| The density wave theory is indeed the currently favored explanation for spiral arms. Your idea for testing it is well thought out and would work as a concept, but would probably be difficult to do in practice, because supernovae are such rare events. You'd really have to look at a large number of galaxies.
I would think that looking for the supernovae would not be necessary since we could instead just look for the massive O & B type stars they originate from. These stars are very luminous and thus easy to see in other galaxies, and as you note they don't live very long before exploding, so they are good tracers to star formation sites. The catch is that you are limited to galaxies near enough to resolve those stars, but that's still a pretty large sample and you are not limited by the rate at which they explode. 
Other ways to test the theory are through computer simulations, and observations of the distributions, densities, and motions of molecular clouds.
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