Neutrinos give neutron stars a chill

This composite optical and X-ray image shows matter swirling around the neutron star at the heart of the Crab Nebula. A new model suggests that neutron star surfaces may be cooled by neutrino emission.

Optical: NASA/HST/ASU/J. Hester et al. X-Ray: NASA/CXC/ASU/J. Hester et al.

Neutron stars—the tiny collapsed remains of the cores of stars much more massive than the Sun—are remarkably complex systems. The inner layers are composed of a form of matter that exists nowhere else in the Universe, while the outermost layer is a "crust" of heavy atomic nuclei. When any matter falls onto the neutron star's surface, it can result in thermonuclear explosions and other, stranger energetic events.

A new study of neutron star nuclear physics showed that these objects might be even weirder than previously thought. H. Schatz and colleagues modeled reactions in the crust and found that much of the energy there is carried away by neutrinos. This involves processes known from exploding white dwarfs (the type Ia supernovas) but which had never been thought to take place in neutron stars. The surprising result is a decoupling between thermonuclear explosions outside the neutron star and reactions deep inside the crust.

When a star roughly 8 times more massive than the Sun runs out of nuclear fuel, its core collapses while the outer layers are blown out in a supernova explosion. If the star is not too massive, the core remnant will stabilize before becoming a black hole. The object's self-gravity is strong enough to crush atoms and nuclei into a dense material that we don't think is found anywhere else in the cosmos. Because much of this material is composed of neutrons, the core remnant is known as a neutron star.