Neutron stars are the densest form of matter that still has any kind of structure. When a massive star exhausts its nuclear fuel, it can explode in a supernova, leaving the ultradense core of the star to collapse on itself. The protons and electrons fuse together to make neutrons, and the whole object becomes basically one massive nucleus. The remnant is a rapidly spinning, highly magnetized star, with more mass than the Sun crammed into a sphere about the size of Manhattan. The conditions inside a neutron star are so extreme, they push our understanding of nuclear matter and particle interactions to the limit. There’s an ongoing debate about what exactly the inside of a neutron star is made of. In some models, it’s a neutron superfluid soup; in others, even the neutrons themselves are fused together and the interior consists of a mush of quarks known as strange quark matter.

If you add enough mass to a neutron star, though, no force of nature can hold it up, and it collapses into a black hole. The critical mass (known as the Tolman–Oppenheimer–Volkoff limit) depends on the nature of the star’s interior, but it also depends on whether or not the star is rotating rapidly. If the star is above that critical mass but spinning, the centrifugal force can help keep the star from collapsing right away. Even if held up by its spin, however, the star constantly loses angular momentum through magnetic braking (when magnetic fields carry mass away along the field lines), so the final collapse is just a matter of time.

Exactly how much time is what everything hinges on. If the blitzar model of FRBs is correct, you need a mechanism to (1) make the star supramassive and (2) keep it from becoming a black hole so quickly that it can’t emit a radio pulse. The original proposers of the blitzar model imagined that the supramassive neutron star might form during the supernova. The uncertainty in the neutron star interior model makes it still unclear whether the collapse would be too fast, or whether enough supernova events would have just the right balance between mass and rotation. Alternatively, the supramassive star might form via a merging of two neutron stars, in which case there may be an association with short gamma ray bursts rather than supernovae. The plausibility of this scenario as well depends on the rates and timescales, which in turn depend on the extreme physics of the neutron star interior. The recent discovery of a four-quark particle at the LHC might even be relevant to this question, as it lends some support to the idea of a “quark mush” neutron star core.

While theorists crunch the numbers to find exciting new ways to explode astrophysical objects, observers are busily hunting for more FRBs in the sky. The current tally is somewhere around 10, and with each new event, we gain valuable information. Correlations between FRB locations and active star-forming galaxies would suggest they come from supernovae, whereas more FRBs close to the plane of our galaxy would lend support to the idea that they’re closer than initially believed. We’re also looking for counterparts at other wavelengths (though we’ve seen none yet) – and maybe even gravitational waves from possible neutron star binaries.