X-Rays
Written by John Carl Villanueva
The image shows in red the X-ray emission produced by high-energy particles accelerated at the shock front where Centaurus A's expanding radio lobe (shown in blue) collides with the surrounding galaxy. (In the top-left corner X-ray emission from close to the central black hole, and from the X-ray jet extending in the opposite direction can also be seen.) Credit: NASA
X-rays are among the high-energy electromagnetic waves, with energies reaching up to 120 keV. They're found near the end of the electromagnetic spectrum, trailing only gamma rays. Basically, they're one of the highest in terms of frequency and among the shortest in terms wavelengths.
They're most common in the field of medicine but are also used in astronomy through X-ray telescopes (XRT). As with practically all bands in the electromagnetic spectrum, the X-ray band overlaps with that adjacent to it. Nevertheless, its wavelengths are somewhere between 0.01 nm to 10 nm while its frequencies are somewhere between 3×1016 Hz to 3×1019 Hz.
X-rays were first discovered in the mid 1870's by Wilhelm Conrad Rontgen while experimenting with Crookes tubes, discharge tubes commonly used in studying cathode rays at that time. The cathode rays were actually electrons fired from cathodes and accelerated along the tubes. Upon hitting the anodes at the other end, they produced x-rays through a phenomenon known as Bremsstrahlung.
Further studies were made on x-rays by other notable scientists such as Nikola Tesla, Philipp Lenard, and Thomas Edison. All these led to its extensive use in diagnostic radiography as well as the discovery of the x-ray microscope.
As mentioned earlier, x-rays are among those electromagnetic waves carrying high energies. This is due to their high frequencies. Because of their large energies, x-rays are capable of ionizing atoms that they are incident on. This is also the reason why x-rays are considered harmful.
By dislodging say an electron, x-rays are able to alter the inertness of the atom since it will now readily interact with adjacent atoms. This is due to its newly acquired charge. If an atom loses an electron, for example, it becomes positively charged, and can in turn attract neighboring electrons.
These high-frequency electromagnetic radiation are also used in astronomy (see the image above). X-ray astronomy typically deals with the study of x-rays emitted by celestial bodies. Just like UV radiation, x-rays are easily dissipated by certain components in the atmosphere. As such, XRTs are stationed high above the earth's surface, e.g., on satellites.
High resolution XRTs are commonly used to study part of the life cycle of solar magnetic fields. A typical XRT is made up of X-ray as well as visible light optical components, filters, shutters, CCD cameras, and a data processor.
Some of the satellites that are equipped with x-ray detectors are the XMM-Newton Observatory, the INTEGRAL satellite, the Rossi X-ray Timing Explorer (RXTE), and the Swift observatory.
You can read more about x-rays here in Universe Today. Want to know about how the 25-year old mystery of X-ray emissions was solved? We've also written about how astronomers resolved Milky Way's mysterious X-Ray glow
There's more about it at NASA and Physics World. Here are a couple of sources there:
X-Ray Astronomy
X-ray Beams Thin Out
Here are two episodes at Astronomy Cast that you might want to check out as well:
X-Ray Astronomy
Optical Astronomy
Filed under: Astronomy
Tags: electromagnetic radiation, ionizing, X-ray, XRT
