In late June 2013, an exceptional binary system containing a rapidly spinning neutron star underwent a dramatic change in behavior never before observed. The pulsar's radio beacon vanished, while at the same time the system brightened fivefold in gamma rays, the most powerful form of light, according to measurements by NASA's Fermi Gamma-ray Space Telescope. The system, known as AY Sextantis, is located about 4,400 light-years away in the constellation Sextans. It pairs a 1.7-millisecond pulsar named PSR J1023+0038 -- J1023 for short -- with a star containing about one-fifth the mass of the sun. The stars complete an orbit in only 4.8 hours, which places them so close together that the pulsar will gradually evaporate its companion. To better understand J1023's spin and orbital evolution, the system was routinely monitored in radio. These observations revealed that the pulsar's radio signal had turned off and prompted the search for an associated change in its gamma-ray properties. What's happening, astronomers say, are the last sputtering throes of the pulsar spin-up process.
Credit: NASA/Goddard Space Flight Center
