This is CBS, I'm the world. I'm John Dott. So I welcome Dr. Ken Croswell, writing most recently at Science News about the stars in our beautiful galaxy and distinctions made between a red dwarf and a brown dwarf.

Ken is the author of the Lives of Stars in the Alchemy of Heavens. So I follow his lead when we come to this very particular language about stars. We have a beautiful star. It is main sequence Ken teaches me, but not all stars are main sequence.

And the most popular that is to say the most numerous star in the galaxy is a dwarf or red dwarf. Ken, very good evening to you. What does it mean when you call a star a dwarf or a brown dwarf or yellow dwarf or blue dwarf? What does dwarf mean? Good evening to you.

Good evening, John. Unfortunately, this term is not terribly well used by astronomers in my opinion. For most stars, they'll not all. The term dwarf means that the star is engaged in nuclear reactions that convert hydrogen into helium at its core. It is a main sequence star.

That's the case for the sun. That's the case for these red dwarfs that we are going to be talking about. It is, however, not the case for the brown dwarfs that we're going to be talking about. Nor is it the case for white dwarfs, which are whole nether types of stars.

Of star that hopefully we're not going to be talking about because we've already got two types of stars here to worry about. That's the red dwarfs and the brown dwarfs and red dwarfs are main sequence stars. They are very hydrogen into helium at their cores just as the sun does.

They were much fainter and smaller and cooler than the sun because they were born with less mass, certainly less mass than the sun, somewhere between 7% of the solar mass and 60% of the solar mass.

They shine very dimly. They burn their fuel very frugally and some of them are going to live more than a trillion years. That's older than the age of the university.

The university is 13.8 billion years old. Some of these red dwarfs are smallest of the least massive of them will live for over a trillion years. These are very, very long lived objects and they're very common.

Most stars in the Milky Way are red dwarfs. They're very nearest to the sun. Proximal centauri will cage us over four light years away is a red dwarf.

The brown dwarfs then are now we come into the distinction made between the brown dwarfs and the red dwarfs is a brown dwarf also dim and what does it burn?

Brown dwarfs are also dim. Yes, they're also small. When young, they do shine in a red color so you can see them if you have a good enough telescope with your eye. They are emitting visible light.

The light though is coming from the glow of its birth, the heat of its birth. In fact, by the way, at the sun, a lot of people don't know this, but the sun is for many millions of years.

It was shining quite brightly, not because of nuclear reactions, but simply because gravity was squeezing the sun, squeezing its gas, causing the gas to heat up.

And a lot of physics, anything atop, it's visible light. So if you had visited the sun when it was 10 million years old, you were seen it shining brightly.

But that brightness came not from nuclear reactions, but simply from the heat of the sun's birth. And likewise, brown dwarfs, which are much dimmer than the sun, they wonder young, they shine and they emit visible light.

And then what's different about the brown dwarfs is their nuclear reactions, they do have some nuclear reactions going on, but those nuclear reactions is a lot because they were born with two little masks. They were born with less than 7% of a solar mask.

So unlike the red dwarfs, some of which will live for over a trillion years, the brown dwarfs, they fade out. And in fact, it was only, as you might have had, it's not easy to detect such stars. And we only detected the first of them in 1995.

So when you were a kid, people didn't know about brown dwarfs.

Are there many brown dwarfs like red dwarfs? Are they commonplace?

Brown dwarfs are also very common. In fact, within just eight light years of the sun, there are three brown dwarfs that we know about. They're out of commoners' red dwarfs, but they're still very common. So yes, both red dwarfs and brown dwarfs are common.

You have taught me that red dwarfs have planetary systems and that the here to four it was thought those planetary systems could not sustain life. Now that opinion is no longer holding sway. Do brown dwarfs have planetary systems?

...