Ever since their discovery three decades ago, neutron stars have fascinated astronomers. They have extreme properties in almost all respects: they are the densest objects in the Universe, the most rapidly rotating, and the best astronomical laboratory for condensed-matter physics. To this, Kouveliotou et al. (page 235 of this issue) add direct evidence of magnetic fields strong enough to perturb the very structure of the vacuum. First a bit of background. Pulsars — pulsating radio sources — are the most common manifestation of neutron stars. When they are born in supernova explosions, pulsars are believed to be rotating rapidly, with periods of tens of milliseconds, and to have magnetic fields of about 10 gauss (10 tesla).
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