A team of astronomers has used an earthquake model to understand perturbations in the timing of pulsars. Their results suggest that pulsars could have a much stranger interior than meets the eye.
Pulsars are perhaps the most accurate timekeepers in the entire universe. The pulsars themselves are really fast rotating neutron stars. Neutron stars are ultradense spheres of atomic matter, typically no larger than a few kilometers in diameter and with a mass a few times that of the Sun.
As these neutron stars spin, they emit beams that make circles across the sky. If the Earth happens to be on one of these circles, we see periodic flashes of these radiation rays, creating a pulsar.
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Pulsars maintain precise rhythm for incredibly long periods of time. But occasionally they are known to glitch when they suddenly switch from one rotation rate to another.
Astronomers don’t quite understand what causes the glitches, but recently a team of researchers put together a model showing how glitches work. The model is based on earthquakes. Earthquakes have many causes, but one of them is when too much stress and pressure builds up between tectonic plates and the earth’s crust buckles under the pressure. The result is an earthquake and a resettlement of the material in the ground.
Neutron stars can also experience tremendous pressures in their complex interiors, with components of the neutron star material pressing against other parts. When the pressure becomes too great, the neutron star rearranges itself, triggering a starquake and a realignment of its own interior. With the new mass distribution within the neutron star, a new rotation speed results.
With this earthquake model, the researchers tried to find out what is inside neutron stars. The deep cores of neutron stars could be neutrons in a very exotic state, or a degenerate form of matter composed almost entirely of strange quarks.
The researchers found that the neutron star interior model, which contained strange quarks, was better able to generate disturbances through a starquake mechanism.
Astronomers need more observations to test this idea, but it shows how the observational features of neutron stars can give us clues about their mysterious interiors.