The Black Widow Pulsar

The so-called "Black Widow" pulsar was discovered in 1988 by Fruchter et al. The pulsar has a pulse period of 1.6 milliseconds and is in an eclipsing orbit with a companion. The signal from the pulsar is delayed, causing the period to lengthen, a few minutes before eclipse and for about 20 minutes after the pulsar reappears. This time delay arises because the signal must travel through the ionized plasma surrounding the companion. It is believed that most of the companion's material lies well beyond its Roche Lobe, and that this outer material is being blown off the companion by the neutron star. Calculations suggest that the "black widow" will evaporate away its companion in about a billion years.

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