Galactic Bubbles 
Nothing beats the aroma of bread that's fresh out of the oven. Get in close for a good sniff, and you even feel the heat, which helps carry those sweet-smelling molecules.
Similar processes are at work in the heart of the Milky Way galaxy. The galaxy's core is shaped a bit like a loaf of bread. Gases are rising from the ends of this bar, and for the same reason that they rise from a loaf of bread: it's hot.
In the case of the galaxy, the heat comes from exploding stars. The galaxy's spiral arms funnel material toward the core. When this gas reaches the bar, it piles up and quickly forms new stars. The biggest and heaviest of these stars live short, spectacular lives, then explode. The explosions create big bubbles of gas that rise away from the galaxy's disk.
A team of astronomers has been studying these bubbles with radio telescopes in the United States and Australia. They've found that as they move away from the disk, the bubbles condense to form big, thick clouds -- like the clouds that gave birth to the stars in the first place. The clouds are found around the entire disk, but they're most common around the ends of the bars -- regions where lots of new stars are born.
Over time, the clouds cool and condense, then drop back into the galaxy's disk. Their material mixes with other clouds in the disk to give birth to more new stars -- which may create more big bubbles as they, too, expire in spectacular fashion.
Script by Damond Benningfield, Copyright 2010