Neutron stars may emit most of their neutrinos in just a few beams unevenly across their surface, causing cracks to open. The finding could explain why some neutron stars seem to jerk as they spin.
When some massive stars exhaust their fuel, they collapse and become incredibly dense objects made mostly of neutrons. These neutron stars do not produce heat but can be 60,000掳C on the surface. To cool down, instead of emitting light, they emit neutrinos.
at Western Michigan University and his colleagues developed a mathematical theory and used computer calculations to find out whether neutrino emissions occur in a uniform way across the surface of the star or in a few select locations.
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The researchers focused on the crust, which is the outermost kilometre of a neutron star. Here, neutrinos are created either when protons and electrons combine or neutrons decay. Because some of these processes include negatively charged electrons, they are affected by the star鈥檚 magnetic field.
The researchers found that the magnetic field steers electrons into specific trajectories and constrains where within the crust the most neutrinos are produced. In their calculations, neutrinos only emanated uniformly from the entire surface if the star had a very weak magnetic field. For stars with very strong fields, most neutrinos exited in two large light-show rays at each pole, while for intermediate values it was more varied.
鈥淭hey can squirt neutrinos out in different directions at different rates,鈥� says Famiano. 鈥淥r spray the neutrinos in a cone or in a disc-shaped configuration from the equator.鈥�
Parts of the star where the most neutrinos are emitted would cool down faster than the rest of it, and the temperature difference could then cause the star鈥檚 crust to crack, he says. Neutrinos are notoriously difficult to detect so researchers can鈥檛 obtain a direct image of how they are radiating out of a neutron star. However, neutron stars have been observed to glitch 鈥� to briefly and jerkily speed up as they spin 鈥� which could be related to such cracks forming.
at the University of Maryland says that detailing the neutron stars鈥� cooling process can help researchers understand what is happening inside of them, which is something that can鈥檛 be studied in the lab. The new work shows that strong magnetic fields can focus neutrino emissions into different shapes, but the question remains which shapes are most prevalent and whether the fields are always strong enough for that effect to cause glitches, he says.
Famiano will present at the fall meeting of the American Physical Society鈥檚 Division of Nuclear Physics in New Orleans, Louisiana, on 28 October.
