Pulsar symphony

At the end of its life, if a star is massive enough - say 15 times the mass of the Sun - it will go supernova. This violent explosion throws much of the star outwards into interstellar space leaving beautiful expanding remnants. However, the inner parts of the star collapse inwards, becoming so dense that the electrons and protons are squeezed together to form neutrons and ghostly particles called neutrinos. The neutrinos don't interact much so head out merrily into space leaving the neutrons behind. As most of the matter making up the star now consists of neutrons, it gets called a neutron star.

The original star would likely have been spinning like big balls of stuff tend to do while sat in space. When the supernova explosion occurred, and the core collapsed inwards, it spun up in the same way that an ice-skater spins up as they bring their arms inwards. In fact, they can spin up so fast that they can rotate several hundred times per second. They also have strong magnetic fields and charged particles on the surface get funnelled out along the magnetic poles, emitting radio waves as they accelerate. This results in two beams of radio waves, one from each magnetic pole, giving the radio equivalent of a cosmic lighthouse. These pulsating neutron stars, or pulsars, were first discovered by Jocelyn Bell in 1967. After nearly forty years of research, over 1500 pulsars have been found.

Now you can't look through a radio telescope, so usually they are connected to a chart recorder or a computer to record the brightness of the signal. An alternative is to connect the output to a speaker and listen. Astronomers at Jodrell Bank did exactly that, with measurements of pulsars, so that you could 'hear them'. There is a nice page of pulsar sounds that includes the Crab pulsar rotating 30 times per second and the fastest known pulsar - PSR B1937 21 - rotating 642 times per second. Actually, its period is very accurately known - it is 0.00155780644887275 seconds! Dr Michael Kramer also put together the sounds of pulsars in the globular star cluster, 47 Tucane which makes for interesting listening. You can also see a movie which flys-through the cluster, although I should warn you that it is 40 MB so you will probably need a fast connection.

Posted in astro blog by Stuart on Sunday 12th Jun 2005 (12:24 UTC) | Permalink
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