Where stars form

Yesterday we were treated to a stunning image on the Astronomy Picture of the Day website, which showed off one of the regions in our galaxy where stars are in the process of forming. The image is shown below in infrared light, using data from NASA's Spitzer Space Telescope.

The W33 star forming region as seen in infrared light (Credit: NASA / Spitzer Space Telescope)

This region is called W33, so called because it was the 33rd object catalogued by Gart Westerhout in his survey of radio sources in our Galaxy. Many of the sources catalogued by Westerhout are regions in which stars are forming, such as this one.

Astronomers refer to these regions as massive star forming regions, not just because they are massive (this image is about 100 light years wide!), but also because they are the sites where massive stars are forming. Massive stars are the hottest and most luminous stars that exist, and they play an important role in how a galaxy evolves thanks to their luminosity, the strong winds that emanate from their surfaces, and the supernova explosions in which they end their lives.

For these reasons, and because of their short lives and inherent rarity, massive stars are important objects to study. Furthermore astronomers aren't entirely sure how they form, so regions such as this where massive stars are known to be forming, are important to study.

Star clusters in the Andromeda Galaxy

Today's APOD (Astronomy Picture of the Day) is a stunning image of the Andromeda Galaxy in which many of the galaxy's star clusters can be seen. This beautiful image comes from the Subaru telescope and shows one of the outer spiral arms of the galaxy. In this image the blue patches are young star clusters containing lots of bright young stars, while regions where stars are forming show up as red blobs (because the dust in these regions reddens the light from them). So this image shows us both the places where stars are forming and the locations of recently formed stars.

This image highlights one of the useful properties of star clusters: because they are so bright we can often see them from a long way away, in this case from 2.5 million light years away, the distance to the nearest spiral galaxy (other than our own Milky Way), Andromeda. This means we can use the young star clusters to map out where stars have recently formed and how many stars have formed (by adding up all the light from the young star clusters). Because in the case of Andromeda we can see the entire galaxy (because the disk is inclined towards us, unlike our Milky Way disk which is edge-on and therefore obscures itself) we can map out the star formation across the entire galaxy.

This is an example of how it can sometimes be easier to map out some process (in this case star formation) across a large area for a distant galaxy than it is for our own Milky Way.