Stellar Nurseries

In This Chapter

V Exploring the stuff between the stars

V Emission nebulae and dark dust clouds

V How interstellar clouds form stars

V Molecular lines: radio astronomy between the stars

When you look at the night sky far from city lights, it's hard to miss that there is a lot of blackness up there. There is "space" between the stars. A whole lot of it, apparently.

But, as we've just seen, just because something is black doesn't mean nothing is there. We may just have to look harder.

Like ripples in a pond, planetary nebulae and supernova remnants move away from their parent stars, gradually fading and becoming part of the space between the stars. All of the heavy elements produced in a supernova explosion are sent back out into space. Some astronomers exclusively study these dark places between the stars. These regions are called interstellar space, and the material that we find there is called the interstellar medium.

To be sure, most of space is a more perfect vacuum than is found in any earthly laboratory. But what we call the interstellar medium is filled with radiation, magnetic fields, and (in some places) vast clouds of gas and dust. These gas clouds are waiting in the wings of the galaxy. They are the raw materials from which the next generation of stars will form.

Nor is interstellar space all dark. In fact, some of those points of light that you see in the night sky aren't stars at all. A few of them (like the Great Nebula in Orion) are regions of ionized gas around hot O- and B-type stars. While much of the Milky Way is hidden from optical view by the interstellar medium, radio-frequency and other observations have opened new windows. With high-resolution observations available at many wavelengths, we are now able to witness the birth, evolution, and death of stars. Of course, we have to view a number of different stars at each of these stages, but that is always a limitation in astronomy.

"Nothing?" Shakespeare's King Lear observed to his daughter Cordelia. "Nothing will come of nothing." But, in space, many things come from what is apparently nothing. In this chapter we look at these dark (and not so dark) places between the stars.

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