To my mind the most interesting type of degenerate star is the neutron star. Lumped into this same category is also the spinning version, which unfortunately is given a completely different name. It turns out that a spinning neutron star is called a pulsar.
It was Jocelyn Bell who discovered the first pulsars in 1967 (now known as Dame Jocelyn Bell-Burnell) . She was a graduate student at the time, and is still doing science today.
At one point I had a job interview at the University of Oxford and had the great privilege to be interviewed by Dame Burnell herself. I did not get that position, yet will always remember that interview.
Dame Bell-Burnell observed the sky at radio wavelengths, and noticed that whenever she looked towards a particular region of sky now called the Crab Nebula she found what appeared to be a regular ‘pulsing’ sound.
This was hard to explain, and at first was given the pet name of Little Green Men (LGM), as if only an intelligent species elsewhere in the universe would be able to produce such a regular sound that effectively said, ‘We are here, we are here, we are here.’
To find out the real solution, let us recall what was known at the time. At the time we did know that a star exploded as a supernova in the Crab Nebula 1000 years ago which was recorded by astronomers in China at the time. We also already knew that one potential outcome of a supernova is a neutron star (with the other possible outcome a black hole).
Let us also recall that a neutron star is not an ordinary type of star at all. It is not even made of gas like stars but rather is composed of neutrons. It also releases light not all over its round surface like our sun, but instead over only a very small surface near to the north and south magnetic poles. Apart from the poles, the neutron star is black.
What if a neutron star was oriented such that one of its magnetic poles was pointing straight at us? Then on each rotation it would send a quick flash of light in our direction. This effect is analogous to the lighthouse. We see flashes of light coming from a lighthouse at night because the light is rotating in circles. We do not see the lighthouse structure at all (at night), so it also is essentially dark except for the flashing light.
In the end indeed these regular pulses were found out to be caused by a spinning neutron star. Now we know such objects, the pulsars, can spin as fast as 1000 times per second, and may responsible for producing a substantial amount of X-ray and gamma ray light. As I write this blog entry I am again in England. Let’s see what astronomical news this trip brings.
