What would a pulsar look like close up?Posted: June 13, 2009
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I was in a long discussion at work about pulsars when a slightly odd question hit me. What would a pulsar look like close up? In sci-fi films and TV series often a spaceship or spacestation is orbiting a planet covered in continents and oceans like the Earth or swirling clouds a la Jupiter. Sometimes they may even be in orbit close to a star with spectacular coronal loops reaching up to lick at the craft’s hull. But what would the view from such a craft be if it were circling a pulsar? Let’s leave aside the fact that you may get fried by the radiation coming from the pulsar and consider what the surface of one of these objects is actually like.
A pulsar is a rapidly spinning neutron star, the dense remains of a star more than eight times the mass of the Sun that has spectacularly exploded in a supernova. What is left is 10-20km across, 1.4 to 2 solar masses and rapidly rotating.
These fire out massive amounts of radio emission from their magnetic poles and when one of these points towards the Earth a radio pulse is detected. As these objects spin so fast many pulses a second can be detected, hence the name pulsar. In the centre of the swirling X-ray emission in the picture on the left is the Crab Pulsar (Credit:NASA/CXC/SAO). This remnant of a supernova explosion seen in 1054 spins 30 times per second. As well as radio emission, the pulsar emits bright visible light from the area near each pole in addition visible light from its hot surface.
As you can probably guess neutron stars are quite dense. Imagine if it started snowing flakes with the density of the material in a neutron star. Two inches of this neutron star snow covering Amsterdam (or just one inch covering Andorra) would have the same mass as the Earth. It is thought that these objects have a solid outer crust a few kilometres thick with some kind of fluid interior. Like on the Earth this crust can sometimes fracture and this causes a
starquake. These can be used to tell a bit about the internal structure of the star. What would these quakes look like? Well there is this
rather cool animation which seems to show fractures in the surface. One study predicts that neutron star crusts may be strong enough to support mountains despite the extremely high gravity of these objects. But these would only be a few centimetres high so clearly this is the Danish definition of a mountain.
So neutron stars have quakes causing fractures in their surface, brighter optical emission from each magnetic pole and maybe (very, very, very small) mountains. However you have to remember these things are going round tens or (in the case of millisecond pulsars) hundreds of times a second. Hence any surface features would probably be blurred out when viewed from our hypothetical spacecraft. So what would a pulsar look like close up? Well my best guess is like this.