Physics Photo of the Week

March 6, 2009

Crab Nebula - Photo and discussion by Kaylee Dunn

In the year 1045 CE Chinese astronomers observed a supernova which at the time was brighter than Venus. The supernova's remnants are now visible through telescopes as The Crab Nebula which is stretching out into space at an average of 2 arc seconds per year. It has spread to about 10 light years in diameter.

During a supernova a star explodes, the outer layers burst out into space creating a nebulous region, highly polarized blue light is emitted by energetic electrons moving through strong magnetic fields in a process called synchrotron radiation.  A simple calculation shows that the magnetic fields responsible for visible-light synchrotron radiation are about 500 million times larger than the Earth's magnetic field (assuming the electrons are non-relativistic).   The center of the supernova collapsed under the weight of it's own gravity. The immense amount of gravity created a neutron star - an extremely dense object.  A cubic centimeter of neutron star material would weigh two billion tons on Earth.

On November 9th, 1968 a pulsating radio source was detected in the Crab Nebula by the Arecibo Observatory in Puerto Rico. The source was found to be the rapidly rotating neutron star. The "Pulsar" in the center of the nebula rotates about 30 times a second while emitting pulses from every part of the electromagnetic spectrum.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to 

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