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More Than Meets the Eye
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There's more to the universe than meets the eye.
Our eyeballs pick out and process only visible light --- it's how we see. "Only" seeing visible wavelengths is more than enough for us to survive and enjoy life on our wonderful planet. But it's a hindrance to those hyper-curious science types. Astronomers want to know what is going on in all those other wavelengths of light, the ones unseen.
Take X-rays, for example. We have all experienced X-rays from visits to the radiologist or dentist. There a beam of X-rays is fired through you. Those X-rays not stopped by dense material like bone make it through to the other side where a photographic plate absorbs them. That gives the doctor an image of what's going on inside.
But the dose is very small --- it has to be. X-rays are one of the most energetic and dangerous forms of light in the universe and they spew heavily from all kinds of heavenly objects. When something Out There is heated to millions of degrees it gives off the sinister rays which radiate throughout the universe. But, curiously, they have little to no effect on us on Earth. Why?
The atmosphere absorbs them for us. Without this protection from above, we would be bathed in deadly X-rays day and night --- a fatal bath we do not want to take. Now that's great news for us, but annoying news for X-ray astronomers who desire the extra information X-rays can give us.
The most logical workaround for this problem is to fire off an X-ray telescope into orbit, above the atmosphere. And that's exactly what astronomers have done over the last decades. Among the several up there now is NASA's cutting-edge Chandra X-ray Observatory, named after the astrophysicist Subrahmanyan Chandrasekhar.
So what can be "seen" in the X-ray universe? An extraordinary amount of bizarre phenomena, that's what. (For the following examples, thinking caps are required.)
X-rays can betray the positions of black holes for example, those now legendary denizens of space with gravity so severe that having fallen into one, nothing escapes, not even light. Though by definition black holes are "unseeable," they suck into them gases from nearby stars with such voracity that the inflowing gases heat up, giving off X-rays as they do, thus revealing the location of the black hole.
Another exotic entity, an X-ray burster, is an object in the sky that emits a sudden and profound burst of X-rays. Long a mystery, astronomers now think that they emanate from double-star systems in which one star is a neutron star.
A neutron star is the dead core of a star, about the size of a large city. But it is the proud owner of a powerful gravitational field that strips hydrogen gas off its nearby partner star. As the gases fall onto the surface of the neutron star they are compressed and, through a slightly complicated process, become helium. This itself gives off X-rays. But it gets worse ...
When the neutron star accumulates only about a three-foot layer of helium, the helium, under such immense pressure from the neutron star's gravity, suddenly and violently ignites, instantly reaching temperatures of tens of millions of degrees and giving off a swift burst of lethal X-rays.
X-ray astronomy can also teach us about the sun, comets, the planets, stars, galaxies, and even intergalactic space --- a whole cornucopia of cosmic things. X-ray astronomy, even though steeped in the invisible realm, is helping us to see the universe in a new light.
Questions or comments? Mark Ritter can be reached here.
(Photo courtesy Astronomy Picture of the Day, D. Wang (UMass) et al., CXC, NASA)
Posted by Administrator at 2002.01.19 03:17 PM | Comments (0)
