Do X-ray Astronomers Wear Lead Aprons?

Dr. Patrick Slane from the Chandra X-ray Center presented an overview of the Chandra X-ray Observatory to NASA's museum alliance. This part of the conversation talks about how X-ray Astronomy connects to medical X-rays and what people experience with X-rays from the doctor.

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Everybody is familiar with going to the doctor and having a big X-ray machine kind of point at you and having a film put somewhere and then getting a picture. And at many times, I’ve been asked the question, is it dangerous to shine all those X-rays out in the space from Chandra.

And the answer is, well, we don't do that. Chandra is not an X-ray machine; Chandra is an X-ray camera and collector. So the picture here tries to give an impression of what that's all about. And the top part of that image is the better one to start with.

When you go to a doctor's office, there is this machine that-- it's inside a generator that's running at about oh, a hundred thousand volts and generates X-rays.

Those X-rays are beamed at or are sent towards an object like your hand. Many of them go straight through, some of them go through as well; they don't go through the more dense regions like the bones very well.

And so then a camera is used at the other end to record the picture. And the picture really is a sort of a shadow picture. It shows which rays got through and which ones got blocked.

And Chandra is used to-- in a manner that's similar to the film on the camera. So the (bottom part of the image) shows, for example, a galaxy and it shows a gas cloud in between.

And so, I'll tell a story but then I'll tell you why it's not exactly what most of us do. The galaxy on the left there is producing X-rays because it's very energetic, it's got hot stars, it's got strong magnetic fields and such. Those X-rays, on their way to us -or anywhere else in the galaxy or in the univers- go through material, and some of that material gets absorbed.

So if you look at it with an X-ray camera, you could potentially see the thing emitting the X-rays as well as absorption features from the stuff in between. Now the truth is that most of what we do -some people actually do probe the intermediate material that gas cloud stuff by studying the absorbing effects that it has- but most of us actually look straight at the generator. So why would we do that? I mean, if you're in a doctor's office, the only important stuff is about the hand in the middle.

But if you're a tinkerer and a physicist, you might say to yourself, you know, that thing in the big box back there that's generating those X-rays, just what the heck is going on with that?

And that's what we're doing for the most part. We're looking at that galaxy and we're saying, "Okay, there's X-rays coming out of that thing, so there's things in there that are millions of degrees hot or there are magnetic fields in there that are millions or billions of times stronger than the magnetic field of the earth. How does that all work?"

And so in reality, we usually use the telescope to look at the generators themselves.

-Pat Slane
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More information at http://chandra.harvard.edu/xray_astro/medxray.html