X-ray Wavelengths in Astronomy

by SpaceHike.com

More articles in Telescopes

In 1949, the first x-rays from the Sun were discovered, and, in 1962, an X-ray detector on a rocket discovered the first source of X-ray out of the solar system, called Scorpius X-1. The first time evidence was found for the existence of black holes was in 1971 by the Uhuru satellite. In addition, it discovered X-rays from gas in distant galaxies. In 1978, the Einstein Observatory was launched and discovered that some young stars and quasars emit x-rays. The Mir Space Station X-ray Telescope found X-rays from a supernova in 1987, and in 1990, Rosat was launched, discovering 100,000 X-ray sources.

The sky is filled with glowing gas pools and X-ray stars with strange fluctuations. An X-ray is an extremely short wavelength with a type of high energy radiation. X-rays are only given off by objects that are hotter than a million degrees. Earth's Sun will show only faintly in X-rays. The more powerful X-ray sources are the supernova leftovers, black holes, and gas circling pulsars.

In the electromagnetic spectrum, x-rays have wavelengths between 0.01 nm and ten nanometers. These are much shorter than visible light wavelengths. On Earth, doctors use x-rays to reveal the inside of a person's body, but in Earth's upper atmosphere all X-rays are taken in from space. As a result, any X-ray detector needs to be placed above the atmosphere with the help of satellites, or rockets.

There are two types of detectors used in X-ray telescopes. An electronic detector, CCD, is commonly used in optical telescopes, which will record the X-ray numbers hitting it. The other is a proportional counter, similar to a Geiger counter, and used to detect Earth's radiation. This type will create an X-ray that is the same as a color image. X-rays will be taken in by the usual curved mirror, and can be hard to focus. X-rays will only be reflected when striking a metal surface at a small angle, that is, similar to a bullet's graze when it bounces off a wall. All X-ray telescopes will be highly polished metal cylinders, or grazing incidence mirrors, used to focus the incoming radiation.

The first of the grazing incidence mirrors was used on the Einstein Observatory, capturing over 5,000 X-ray sources. The Mir telescope had an X-ray telescope using a coded mask to focus that observed Supernova 1987A giving off lines in the X-ray spectrum. This proved that the exploding star had created radioactive elements. The Chandra X-ray Observatory was launched in 1999 by the United States and is currently providing NASA with information on black holes. To view these images and accompanying article see NASA Kids.


1. Couper, Heather and Nigel Henbest. Space Encyclopedia DK Publishing, Inc.: NY 1999

2. Editors. Secrets of the Universe. International Master Publishing: US. 1999