For more than 50 years, astrophysicists have speculated that inside a superdense neutron star, nuclear matter might flow without any resistance whatsoever—much like electricity does in earthy materials known as superconductors. Now, two teams say they have direct evidence of such bizarre “superfluidity” in a neutron star, and other researchers seem convinced. “I think it’s a defensible claim,” says theorist Krishna Rajagopal of the Massachusetts Institute of Technology in Cambridge. “The only explanation [of the observation] that I’m aware of is the one presented in papers.”
Ordinary superconductivity is weird to begin with. When some metals are cooled nearly to absolute zero, the electrons in them form hard-to-break “Cooper pairs” that flow without resistance. In 1959, just 2 years after physicists worked out that explanation for superconductivity, some of them proposed that similar pairing may happen inside incredibly hot, hugely pressurized neutron stars. The core of a massive star that has died in a supernova explosion, a neutron star consists of neutrons seasoned with a few protons and electrons, and it packs as much mass as one or two suns into a globe less than 20 kilometers across.
Scientists have accumulated indirect evidence for such pairing and superfluidity. For example, spinning neutron stars called pulsars emit clocklike streams of electromagnetic pulses. Usually incredibly steady, that pulsing sometimes speeds up abruptly. Such “pulsar glitches” likely result from brief interactions between the neutron star’s solid crust and superfluid interior.