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Recent Podcast
A Tour of NGC 4696
A Tour of NGC 4696
The Centaurus Cluster is a collection of hundreds of galaxies located about 145 million light years from Earth. (2017-04-19)

How Chandra Does What It Does

NASA: We have booster ignition and liftoff of Columbia, reaching new heights for women and X-ray Astronomy.

Martin Elvis: The main thing Chandra does is take these superb, sharp images.

Cady Coleman: Nothing as beautiful as Chandra trailing off on its way to work

Narrator: When the Chandra X-ray Observatory was launched aboard the Space Shuttle Columbia on July 23rd, 1999, it began a new era of X-ray Astronomy.

NASA: 5, 4, 3, we have a go for engine start, zero, we have booster ignition and liftoff of Columbia, reaching new heights for women and X-ray Astronomy.

Narrator: But what do X-rays from space tell us, and why do we build telescopes to study them? Most people think of light as what we can see with our human eyes. But in truth our eyes can detect just a small fraction of the radiation emitted by objects in space. Martin Elvis, a senior scientist at the Chandra X-ray Center in Cambridge, Massachusetts, discusses why astronomers want to study the sky in X-ray light.

Martin Elvis: So what's X-ray astronomy? You look up at the night sky and you see stars all over the place, stars like our own sun, big ones, small ones, old ones, young ones, but basically all stars shining with fusion power, nuclear fusion. We only see stars as dominating the night sky because we look in this really narrow band of the whole electromagnetic spectrum called the optical range. If you look well outside this range in either long wavelengths or short wavelengths, you don't see the same stars at all, so we tend to talk about X-ray sources. And they're really not stars. The sky in X-rays is not dominated by stars. Instead, it's dominated by something entirely different, that's powered not by nuclear fusion but by another process which is many times more efficient at converting mass into radiation than nuclear fusion is. Since nuclear fusion is the most efficient process we have around us on earth, that's pretty impressive. So X-ray astronomy in one sense is just trying to answer the question, "What is this stuff? When we look at the sky in X-rays, what do we see?" And it's something entirely new, something you would never have guessed just by looking up at the night sky.

Narrator: One of the most exciting things about X-ray astronomy is that it's really in its infancy. The first X-ray satellites weren't launched until the 1960's. Why the late start? The answer is because X-rays from space are absorbed by the Earth's atmosphere. Therefore, X-ray astronomy had to wait for the Space Age and the development of rockets to get its detectors into orbit.

Narrator: And what does Chandra see in the X-ray universe? When matter is heated to really high temperatures, as in millions of degrees, X-rays are produced. Here's more from Martin:

Martin Elvis: The energy of each photon of light in X-rays is about a thousand times that in optical light, visible light. So it also follows that the temperatures that we deal with in X-rays are about a thousand times hotter, so you're looking for processes that are a thousand times more energetic.

Narrator: So in order to understand what is happening in the hot, turbulent regions of space, we need to have X-ray telescopes. Chandra is using its powerful telescope to study such things as material around black holes, the debris from exploded stars, and hot gas that pervades the space between the galaxies. These are phenomena and objects that would simply be invisible in other wavelengths.

Narrator: For more information about the Chandra X-ray Observatory, visit our website at This was a production of the Chandra X-ray Center, Cambridge, Massachusetts. NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory controls science and flight operations from the CXC.

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