Friday, August 07, 2009

Gamma Rays and Cosmic Russian Roulette

Electromagnetic radiation is a physical phenomenon in our universe that all of us interact with on a daily basis. The electromagnetic spectrum categorizes this radiation based on frequency. The visible light that you perceive with your eyes is only a tiny range of frequencies in this spectrum. Frequencies below visible light include infra red, microwaves, and radio/TV signals. Frequencies above visible light include ultra violet, x-rays, and gamma rays.

We know from our own experiences in the modern world that visible light is generally harmless. We evolved in a world bathed in visible light coming from our sun so it’s only natural that our eyes are specialized to respond to those frequencies. We know that infra red is mostly associated with heat. We’ve seen infra red camera footage and know that the heat lamps that keep the fries warm at the fast food place are just specialized light bulbs that radiate most of their energy at infra red wave lengths. Microwave ovens became ubiquitous in the 1980’s and work by pumping electromagnetic energy into food at a specific frequency that makes the water molecules vibrate and heat up. Below microwaves, radio and TV signals radiate from the tops of mountains and man-made towers to bring audio and video into our homes and vehicles. CB radios, baby monitors, Wi-Fi internet, Bluetooth headsets, and mobile phones all do their things down here.

Above visible light, ultra violet frequencies give us sunburn and, if we’re not careful, skin cancer. Light bulbs tuned for ultra violet (aka black lights) are used to sterilize water, instantly dry inks in printing processes, make your hippie posters fluoresce, and make the bowling pins glow during midnight madness. At even higher energies, x-rays pass through objects and allow us to see inside the human body and airport luggage. Excessive amounts of x-ray radiation can cause cancers in animals but can also be tightly focused to destroy tumors. Stars and nebulae often emit x-rays and because of their energy and their ability to pass through matter unimpeded, astronomers often use these frequencies in their research to see farther and in more detail than visible light allows.

Gamma rays are generally thought of as having higher energies than x-rays but the two classifications actually overlap quite a bit. Gamma rays have medical uses similar to x-rays and are employed in sterilization procedures similar to ultra violet. In astronomy, flashes of gamma rays from deep space were first detected accidentally in the 1960’s by cold war satellites monitoring nuclear weapon tests. These flashes were later dubbed “Gamma Ray Bursts” and seemed to originate from the explosions of dying stars.

Gamma Ray Bursts caused considerable controversy amongst astronomers and astrophysicists when they were first identified because they were simply too powerful to exist according to known physical laws. The problem was straightforward. An explosion in space radiates matter and energy in all directions more or less equally. If you detect a gamma ray burst, measure its intensity, and then swing your visible light telescopes around to the same coordinates, you typically (although not always) see the remnants of a novae -- a star that has exploded at the end of its death throes. You can then use various tricks to calculate the distance to that novae and, along with the gamma ray intensity that you measured, determine how powerful the initial explosion had to be based on how much of that energy managed to reach you. All of the gamma ray bursts were determined to be outside of our own galaxy, billions of light years away, and therefore the energy from a symmetrical explosion would have to be the equivalent of all of the energy released by a sun like ours over its entire lifetime based on the level of energy that still managed to reach us from so far away.

Observations later revealed that these calculations were based on a false premise. The gamma ray bursts were NOT symmetrical and in fact were focused into two opposing beams spreading out between 2 and 20 degrees.

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