I'm John Batchler. I welcome Ken Croswell, the astronomer, to help me understand the author of Lives of

Stars and other publications about the heavens. To help me understand a new discovery that was always

logical, but then it had to be found. In 1971, the first black hole is discovered. Since then,

there have been revelation after revelation,

including the enormous grouping of black holes that are at the center of the beautiful Milky Way.

But now we have something entirely unique, which is easy to identify with, a lone black hole.

An orphaned black hole, wandering through the universe.

Ken, a very good evening to you.

What is a black hole before we feel sympathy for it by itself?

Good evening to you.

Good evening, John.

A black hole is a collapsed star with so much density and so much gravity that nothing, not even light, the fastest thing in the universe, can escape.

And as a result, a black hole emits no light.

So it's a very extreme object.

Now, you might wonder, well, then you astronomers can possibly discover these things, since we astronomers rely on light of various wavelengths to do our work.

But black hole does have one thing, and that is it's got mass, and anything that has mass exerts gravitational force.

And so that's how the very first black hole was discovered back in 1971.

And my recent article in the proceedings of the National Academy of Sciences, which is available for free at PNAS.org, I lead off with that discovery.

That black hole is now called Cygnus X-1, and here's how it was discovered.

Astronomers noticed that there was a visible star going around something dark, something that nobody could see. And from the motion of that visible star,

astronomers deduced the mass of the dark object, and it was so massive that it had to be a black hole.

So that's how we discovered the very first black hole in the Milky Way galaxy. Since then, we've only

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