Neutron stars are ultra-dense remnants of dead stars, whose existence was predicted by Fritz Zwicky and whose stability was studied by Subrahmanyan Chandrasekhar. In their cores, matter is squeezed so tightly that a sugar cube would weigh as much as a mountain, and atomic nuclei break down into quarks. According to quantum field theory, these quarks can pair up into a state of color superconductivity — an exotic cousin of ordinary superconductivity.

However, astrophysical measurements have shown that this effect is vanishingly weak.

Stellar masses were determined from pulsars (discovered by Jocelyn Bell Burnell), radii — with the NICER telescope (photometry and spectroscopy of X-rays), and LIGO contributed data on gravitational waves, the trembling of curved spacetime during collisions. Calculations yielded an upper limit for the superconductivity’s influence — about 66 MeV, which is tens of times weaker than the energy of an X-ray photon, and most likely the number is half that.

Such a minuscule contribution means astrophysicists can safely ignore color superconductivity when modeling neutron stars. The exotic phase either emerges at even higher densities or is simply irrelevant for the whole star. Amazingly, this whisper of nature was heard through the roar of cosmic data, a subtle effect fished out of the abyss.