When most people gaze up on a clear, dark night, they are struck by how many stars there are. Astronomers have an opposite reaction: They marvel at the stars’ amazing scarcity. Considering the total amount of raw material available in our galaxy for star formation, there should be up to 10 times the current count. Why, then, does the night sky not blaze with starlight?
It is not a bad thing that there are so few stars; quite the opposite. Stars burn gas, mostly hydrogen. All of the hydrogen gas in the universe was formed during the Big Bang, some 13.8 billion years ago. Each galaxy possesses a finite portion of this primordial fuel, and there is no way to make any more of it. If there were more stars, galaxies would burn through their fuel reserves more quickly and would shine more briefly before lapsing into eternal darkness.
Understanding how stars form and why they are so hard to make does much more than just foretell our far-off cosmic future. Star birth also explains where the atoms in our bodies come from and why the universe looks the way it does today. As astronomer John Bally of the University of Colorado puts it, “Star formation is the single most important process for determining the fate and evolution of normal matter in the universe.” Yet until recently, the details of how stars are born were literally shrouded in mystery: Stars form within dense clouds of dust and gas that block visible light.
Now astronomers are parting the veil with telescopes that detect infrared light, the kind of light central to terrestrial night-vision systems. “Seeing in infrared light is important because the diminution of visible light from inside a dusty cloud can be enormous,” says Judy Pipher, a professor of observational and experimental astronomy at the University of Rochester in New York. “This is not a problem when you use an infrared camera because at those longer wavelengths the cloud will be a million times more transparent.”
