This is CBS, I Am the World. I'm John Baxter. The Milky Way, Dr. Ken Croswell, author of

The Alchemy of the Heavens, has taught me that my favorite galaxy is the Milky Way, same

for Ken. It's beautiful and it turns out it's extremely fertile. Ken, a very good evening

to you. This is exciting work by astronomers in Germany, I believe, discovering the birth

rate of the Milky Way. What did we think then? And what do we think now about the birthing

of stars per year, per million years? Good evening to you.

Good evening, John. Yes, it's very interesting to know how many stars the Milky Way gives

birth to each year. Most galaxies actually don't give birth to any stars at all because

they've literally run out of gas. So for example, most of the galaxies orbiting the Milky

Way do not give birth to any new stars. In the case of the Milky Way, of course, we know

that it gives birth to new stars. We see it happening in all sorts of places like,

for example, the Orion Nebula, the Lagoon Nebula, the Rosette Nebula. And there's a picture

of that on my article in Science News. And so we know that the Milky Way gives birth

to new stars. And of course, four and a half billion years ago, we were one of them. And

the Milky Way does this by converting gas and dust into new stars. And so the question

is, how many new stars does the Milky Way make every year? Or the way astronomers normally

express this, how many solar masses of interstellar gas and dust does the Milky Way convert into

new stars? Before you answer the question, Ken, before you answer the question, let's do

some fundamentals. How does a star form? What does that gas do? And what does it look like?

Ironically enough, in order to make a star, which is very hot, right? That's why stars shine,

because they're very hot. You need very cold gas, because very cold gas has very little outward

pressure. And so if you have very cold gas, as you do in dark clouds throughout the Milky Way,

...