First black widow pulsar found from gamma ray observations

Ars Technica » Scientific Method 2012-10-25

Artist's impression of a black widow pulsar: a rapidly spinning stellar remant that strips matter off a companion star and evaporates it by intense radiation.
NASA/ESA/M.J. Jee and H. Ford (Johns Hopkins University)/Hubble Field), AEI/Milde Marketing Science Communication

Pulsars are the dense, rapidly spinning remains of stars much more massive than the Sun. To really get a pulsar revolving quickly, it needs a companion star: matter stripped from the partner falls onto the pulsar, speeding it up until it can rotate hundreds of times every second. Astronomers discovered these millisecond pulsars by their radio emissions, but many of them are also very strong gamma ray sources.

Astronomers have now used the Fermi Gamma-Ray Space Telescope to identify a "black widow" pulsar that's stripping mass off a close companion star while simultaneously evaporating it by emitting intense radiation. It's having these dramatic effects because the pulsar and its companion orbit each other so closely that they complete an orbit once every 93 minutes, making this the tightest black widow binary yet discovered.

Many radio telescopes are well suited to hunting for pulsars, since they can scan large parts of the sky and pick out the periodic flashes of light these bodies emit. Gamma ray observations are harder for a number of reasons, not least of which is that Earth's atmosphere is (thankfully) opaque to gamma radiation (which means we need space-based telescopes). The only existing gamma ray instrument with the sensitivity to spot millisecond pulsars is the Large Area Telescope (LAT) on the orbiting Fermi observatory.

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