e-Science : April 2012 Issue 1
highest energy particles that exist – to en- ergies much higher than we can achieve on earth with atom smashers like the Large Hadron Collider2 (LHC) at the European Or- ganization for Nuclear Research (CERN) in Geneva. Much of the matter falling toward the black hole is lost forever as it crosses the event horizon. A phenomenon called an accretion disk forms from the in-spiralling matter, and jets of material are blasted out at high velocity at right angles to the disk. Within these jets, some of the particles are further accelerated to even greater energies and are accelerated away from the black hole into space. These accelerated particles may be the cosmic rays3 that we see at the Earth, detected via the giant showers of par- ticles they make in the atmosphere4 . Astronomy with particles Usually, we think of astronomy as a process of looking for light from distant objects arriv- ing at the earth. It’s easy – the light travels in straight lines (except when gravitational lensing5 is present) from the distant objects to us here on Earth. Some of these light particles are so energetic that they get their own special name – “gamma-ray6 .” These gamma-rays have been seen with detectors on satellites orbiting the earth, and using ground-based telescopes7 , which look for the light emitted by showers of particles created when the gamma-rays hit the atmosphere. The highest energy particles that we know of in the Universe are the cosmic rays – which appear to be ordinary protons or heavier nuclei. Their energies are enormous, much higher than we can achieve on earth. They are also electrically (positively) charged so that they get deflected when they travel through magnetic fields out in space. This has the effect that they get scrambled up on their way to Earth – and so we can‘t tell where they came from in the first place. Gamma-rays travel in straight lines but we CreditNASA/SkyWorsDigital VIDEO: A computer animation of a gamma-ray burst destroying a star.
July 2012 Issue 2