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.
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