The Vela X-1 binary consists of a massive blue star and a spinning neutron star. The pair are close enough that the neutron star’s gravity draws in material from its companion’s powerful wind. Because of the neutron star’s intense magnetic field, the material is funneled onto the star’s poles. In the process, the material gets so hot that it emits x rays, which are pulsed because the magnetic and rotation axes are misaligned. NASA’s Swift has been monitoring Vela X-1 since the orbiter’s launch in 2004. That long train of data has given Valentina La Parola of Italy’s National Institute for Astrophysics and her colleagues the opportunity to investigate changes in the neutron star’s magnetic field. Specifically, they tracked a cyclotron absorption line at around 54 keV; the line arises, as in the quantum Hall effect, from the quantization of energy levels in a strong magnetic field. The researchers found...

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