Dark matter: Devourer of stars

NASA's Goddard Space Flight Center

A type of star that I hold dear is the pulsar (a type of neutron star). Not just because the first one discovered was called LGM-1 (Little Green Men), but because they are a rich mixture of quantum physics, electromagnetism, and gravity, all in a single macroscopic object. For a young graduate student, being able to solve a set of equations and describe (at a simple level) the behavior of an entire freaking star is just mind-blowing.

But they are also a huge mystery, having a complex structure and possibly mountains. Another mystery that's not inherent to the objects themselves is that neutron stars of a certain type are conspicuous by their absence in the galactic center. There are many possible reasons for this absence—maybe there aren't any good schools in the neighborhood or it's too far to the local pub—but one of the most exciting possibilities is that the heaviest neutron stars are being hunted down and devoured by dark matter.

Neutron stars are essentially the corpses of stars. After burning through all their fuel and exploding in a last furious burst of energy, the remaining matter collapses in on itself. The temperature and pressure get so high that the electrons and protons fuse to form neutrons. However, their mass isn't sufficient for gravity to force the neutrons together—if it were, a black hole would form. The pressure that prevents a neutron star from collapsing is called the Fermi pressure. Neutrons are fermions, which means they repel each other. Fermions cannot occupy the same quantum state, so at close range, they stack in energy and space themselves out. This unusual state also generates huge magnetic fields, which accelerates charged particles to enormous energies as the star spins. These particles emit beams of radiation that sweep around like the beam from a light house. When we happen to fall in the path of this beam, we record this as a regular blip of light.