They Tell us About the Process of Star Birth

Stars are born in messy litters that spread themselves across the sky for hundreds of thousands of light-years. If you look at one of these creches, you can see bright stars still embedded in the clouds that formed them. You can also see the “seeds” of stars — that is, regions where gas and dust is still wrapped so tightly around newly forming stars that they can’t yet be seen.

What starts a cloud of as and dust down the path of starbirth?  If the cloud just sits there with no outside forces acting on it, it will just stay a cloud. But, give it a little push, say from the strong wind of a nearby massive star (which shoves material along ahead of it), or even a supernova blast, and the cloud starts clumping together and swirling around. Eventually the material in the center, which is being compressed by the motion, will heat up. If this happens long enough and there’s enough material to keep the clumping going, a star will eventually form.  This is a very simple explanation for a complex set of processes that take hundreds of thousands of years to start a cloud down the path of starbirth.

The Spitzer Space Telescope (and other observatories) have long studied starbirth regions to understand the star-and-cloud interactions that seem to trigger the births of new stars. The latest picture from Spitzer (NASA/JPL-Caltech/Harvard-Smithsonian CfA) was just released last week  to help celebrate this infrared observatory’s fifth year on orbit. It shows multiple generations of stars all gathered in a big molecular cloud “family home” — a region called W5. This cloud complex is so big that it spans an area of sky about the size of four full moons. W5 lies about 6,500 light-years away from us in the constellation Cassiopeia.

In this image, the blue dots in the centers of the two hollow cavities are the older stars of the W5 stellar family (other blue dots are background and foreground stars not associated with the region). Younger stars line the rims of cavities in the cloud that were carved out by winds from the most massive stars in the area. Some of the younger stars can be seen as pink dots at the tips of the elephant-trunk-like pillars. The white knotty areas are where the youngest stars in the family are forming. Red shows heated dust that is scattered throughout the cavities. The densest clouds are colored green (and, this is a false-color image; the color-coding is there simply to help astronomers separate various regions and structures in the starbirth region).

This image contains some of the best evidence yet for the triggered star-formation theory. And, it’s a stunningly beautiful illustration of just how much we’ve learned about the births of multiple generations of stars by using some of the most advanced telescopes on and off the planet!