NGC 3628, A Galaxy on Edge |
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This is not what most people would think of if they were asked to describe a
spiral galaxy; aftera ll, where are the beautiful spiral arms? in the case
of NGC 3628 we just happen to be looking at the galaxy edge-on. Instead of
spiral arms we see a very sdistinctive dust lane running the length of the
galaxy. This distinctive feature arises because galaxies do not just contain
stars, they also contain significant amounts of dust and gas between the
stars. Over very large distances the gas and dust can act like a galactic
fog and block starlight from distant stars. The red dots along the dust lane
are regions where hot massive stars are forming, causing the hydrogen gas
surrounding the newly formed stars to glow.
So how do astronomers know this galaxy is a spiral? Fortunately, spiral galaxies also have a bulge of stars surrounding their central regions that you can see in this image. By comparing the size of a galaxy's bulge to its disk, astronomers can gain a good idea of what a galaxy's spiral arms look like even without being able to see them directly. | |