Wednesday, April 02, 2008

Dispatches From NAM

As I'm in Munich on a collaborative visit at the moment I haven't made it to the National Astronomy Meeting this year. As well as meaning Durham were unable to retain the 5-a-side football trophy (as if I would have changed that) it means I have missed out on actually being in the room when some really interesting talks are given. Fortunately some people are live blogging the event here, its a good way to keep up with the goings on and to find pretty pictures like this one to steal:

Most of this picture has been around for a few years. It shows data from the SDSS which essentially shows the density of stars across a particular patch of sky, what is interesting is the number of coherent streams of stars visible. Many of these streams have been traced and found to be associated with dwarf satellites or globular clusters of our galaxy which are currently being torn apart by the gravity of the Milky Way. Whats new about this picture is that a team of astronmers (not sure who exactly, though the talk describing the result was given by Dan Zucker of the Institute of Astronomy) have used the original map to discover several new Milky Way satellite galaxies.

This is interesting in particular because its been known for a considerable amount of time that models of galaxy formation predict that a galaxy the size of the Milky Way should have many more dwarf galaxies than are actually observed. The discovery of more dwarf galaxies is helping to fix this discrepancy, the observation that many dwarfs are currently being destroyed by the MW also tends to lend support to the idea that originally there were many more, they have mostly been stripped and subsumed into the halo of the Galaxy. An additional bonus of the work presented at NAM is the observation that the motions of stars in the dwarf galaxies is much too fast to be explained without the dwarf galaxies being heavily dominated by dark matter, another prediction of current generations of galaxy formation models.

Score one complete (predicting the excess DM) and one partial victory (getting closer to the right number of satellites) for current theory then, there is however a final twist in the tale.
The shapes of the dwarf galaxies is apparently irregular, something that doesn't make that much sense if they are embedded in a larger dark matter halo, this should act to damp out external pertubations (say due to the Milky Ways gravity) and to keep the stars in a more regular shape. Whack one mole, another pops up, such is a scientists lot.