Carbon Monoxide 
Carbon monoxide is nasty stuff. If too much of it builds up in your car or house, it can cause anything from a mild headache to death. For astronomers, though, carbon monoxide is a key to life — it helps reveal the secrets of starbirth.
Stars form in cold clouds of gas and dust. At first, these clouds can span light-years. But a shockwave from a nearby exploding star or some other disturbance can cause such a cloud to collapse. When it gets dense enough, some of its atoms link together to form molecules. The molecules produce energy that can be detected by giant radio telescopes. So astronomers often study starbirth by looking at molecular gas.
By far the most common element in space is hydrogen. But hydrogen molecules are hard to observe because they don’t radiate at the frigid temperatures associated with star-forming gas.
The next most common element in space is helium. But it doesn’t help, either, because it doesn’t bond together to form molecules.
After hydrogen and helium, the next most common elements are oxygen and then carbon. They join to form carbon monoxide, which emits copious amounts of radio waves that radio telescopes can detect. What’s more, it’s laced through the clouds that give birth to new stars. So ever since astronomers first detected interstellar carbon monoxide more than 40 years ago, they've been using it to study the birth of stars. So while this unlikely molecule is a terrestrial poison, it’s also a celestial treasure.
Script by Ken Croswell, Copyright 2013