Yesterday, we brought word of a new kind of mysterious astronomic event, one that created a single, energetic burst of radio waves, but otherwise left no apparent trace. Although there are a lot of things we know about that might cause something similar, none of them are likely to occur with the right frequency or at the right energy to produce the radio bursts. While doing research for that story, however, I came across a paper that describes something we've never seen before, but could hypothetically exist: the blitzar, caused when a neutron star catastrophically collapses into a black hole.

If you're a fan of supernovae—and, really, if you're not, what's wrong with you?—you'd know that they tend to leave extraordinarily compact and dense bodies behind. If they're below a critical mass, quantum effects balance out the pull of gravity by keeping neutrons from occupying the same quantum state. Once the mass gets high enough—technically, above the "Tolman–Oppenheimer–Volkoff limit"—gravity can overwhelm the quantum effects, and collapse both matter and space into a black hole. Typically, this is presented as an either/or: a body is on one side of the mass limit or the other, and its identity is set accordingly.

But that turns out to be true only if there are no other forces acting on the body in question. And, in the real world (or even the somewhat surreal world of the forces interacting in a supernova remnant), there are usually a number of other forces in action. One of these is the fact that the neutron star, when it forms, inherits a lot of the rotational energy of the parent star. Since its radius and mass are tiny in comparison to the star, this means that the neutron star starts out rotating, often extremely rapidly. This rotation could potentially keep a neutron star that's heavier than the Tolman–Oppenheimer–Volkoff limit from collapsing to form a black hole. The authors of the paper describing these bodies, Heino Falcke and Luciano Rezzolla, call them supramassive rotating neutron stars, or SURONs.

(No, I have not contacted the authors to find out if they had Sauron in mind when coming up with the name.)

Many neutron stars also have intense magnetic fields. Over time, through their interactions with the environment, their magnetic fields will put a brake on the rotation, gradually slowing the star. Once rotation slows enough, the Tolman–Oppenheimer–Volkoff limit will kick in, and the SURON will collapse into a black hole in a matter of milliseconds.

All of the material of the star itself will end up on the wrong side of the event horizon to leave a trace in our Universe. But most of the magnetic fields' lines end up on the other side of the event horizon—the same side that we're on—and suddenly find themselves separated from the body that had been powering them. According to theory (literally called the "no-hair theorem"), physics isn't happy about having magnetic fields lines cross the event horizon, so everything on the outside will instantaneously detach from the neutron star and reconnect on the outside of the black hole.

"This results in large currents and intense electromagnetic emission," the authors write, going on to say, "a strong magnetic shock wave moving at near the speed of light is indeed seen in 3D resistive magnetohydrodynamic simulations of the collapse of non-rotating NSs [neutron stars]." This shock wave will dramatically accelerate any ions in the neighborhood, creating a sudden burst of light. This the authors term a "blitzar."

Using estimates of the total number of core-collapse supernovae, the authors estimate that only three percent of them would need to form SURONs to create roughly the right frequency to account for all the radiowave bursts described in the Science paper. But for this to work, all of them will have to be both spinning rapidly enough to keep them from collapsing and have a magnetic field that's strong enough to slow them down. At the moment, we don't know whether this is a typical condition. So, for now, the SURON remains a creature of pure theory.

The arXiv. Abstract number: 1307.1409 (About the arXiv). To be published in Astronomy & Astrophysics.