A Science Odyssey 'Little Green Men'
Little Green Men


Ricky: Hey, man. This is Ricky Riles reporting from Cambridge, England.

I'm standing in the middle of an enormous field filled with poles and wire. No, this isn't the world's longest clothesline. It's actually a really groovy antenna. A four and a half acre antenna. Its purpose: to scan the cosmos for radio signals from outer space.

Several months ago this antenna received a very special signal. A signal sent by "little green men" from outer space.

Ricky: Standing here with me is graduate student and astronomer Jocelyn Bell. What's hap'nin', Jocelyn! Hey, I hear you helped build this antenna.

Jocelyn: Ah, yes, I worked with several other students for an entire summer swinging sledgehammers and stringing 120 miles of wire and cable.

Ricky: Right on, sister!

Jocelyn: A moment ago you said that we received a signal from "little green men." In fact, we do not believe that the signal is from "little green men" at all.

Ricky: You don't think the signal was sent by little green men? Maybe it was sent by beings with gray skin, large bald heads, and big, wide eyes, then.

Jocelyn: That's very funny. Actually, we don't think the signals are from an intelligent source at all. But we did at first.

Jocelyn: The signal appeared on our instruments as pulses of energy. The pulses were very regular -- like clockwork. Every one and one third seconds we'd see this blip on our chart paper.

The speed of the pulse -- one and one third seconds -- was far too fast to be created by anything as large as a star. That's why we thought the signal was being sent by an intelligent source. That's why I said, as a joke, that it was coming from "little green men."

Then, about a month later, I found another signal. But this one, pulsing every one and a half seconds, was from the other side of the sky.

Now what are the chances that two very distant sources would be sending very similar signals towards earth -- at the same time, no less? Not very high, to say the least.

Ricky: Bummer, man. A radio rap session with a couple of dudes from outer space would be far out.

Jocelyn: Ah... yes, wouldn't it. Anyway, the fact that we have two distinct sets of signals suggests that the sources are stellar and not from green men. In other words, these radio signals are from a star or other object in our galaxy. We now call these stars pulsars.

Ricky: I can dig it.

Jocelyn: At first we couldn't imagine what might cause such a speedy, consistant signal. I must say, there was considerable debate and many theories were thrashed about. The one that was settled on, though, is that the source is a neutron star.

Ricky: Heavy, man.

Jocelyn: Actually, a neutron star is heavy, very heavy, but not in the sense that you mean.

A neutron star is exceedingly dense. It has the same amount of mass as our Sun (which means it weighs about the same), but instead of being a 865,000-mile-wide sphere, all of its matter is squeezed into a sphere that's only six miles wide.

Having all this matter in such a small volume has a strange side effect: it produces a very intense magnetic field. This magnetic field is a million million times stronger than the Earth's. It is this magnetic field that produces radio waves.

These radio waves shoot straight out from the star's magnetic north and south poles.

Neutron stars spin at a constant rate -- just as the Earth does -- this is the reason we see regular pulses of radio waves. As the star spins, its radio waves shoot out into the galaxy. Anything in the path of the waves will see a pulse of radio energy. It's similar, in a way, to a lighthouse.

Ricky: These pulsars sound really far out.

Jocelyn: I think so, but we don't know exactly how far out.

Ricky: Well, thanks, Jocelyn. Good luck, and keep on keepin' on.

And there you have it! This is Ricky Riles.

The End

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