Monday, December 12, 2011

Step up to the bar - the Milky Way bar

Apparently there's a bar/box shaped concentration of stars in the center of our Milky Way galaxy.

This central bar is oriented about 20 degrees from our line of sight to the center of the galaxy - so the diagram above doesn't look quite right to me. The bar seems to rotate like a cylinder - rigidly. This type of structure is typical of many galaxies, not just ours. There's evidence that our bar is a fairly uniform population, there's no real evidence of recent mergers. That's inconsistent with a model of galaxy formation by merger, which seemed to work well for elliptical galaxies. Our Milky Way is a barred spiral - different from ellipticals - but it was thought for a while that the central bulge of spirals might have formed a similar manner. Now that no longer appears to be true.
For some scientific details see The Bulge Radial Velocity Assay (BRAVA): II. Complete Sample and Data Release and OUR MILKY WAY AS A PURE-DISK GALAXY—A CHALLENGE FOR GALAXY FORMATION.

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