Friday, September 13, 2013

Superheated by a Pulsar

Using data from NASA’s Fermi gamma ray space telescope, astronomers have found an unusually massive gamma-ray pulsar with a light-weight companion in orbit around it. This heavyweight pulsar is identified as PSR J1311-3430 and it is estimated to weigh no less than twice the mass of our Sun. A pulsar, also known as a pulsating neutron star, is an extraordinarily dense remnant of what was once the core of a massive star. PSR J1311-3430 packs over twice the mass of our Sun in a volume of space measuring just a few kilometres across. A teaspoon of its material would contain a mass amounting to billions of metric tons.

Artist’s impression of a neutron star. Credit: Vadym Sklyaruk

PSR J1311-3430 emits prodigious amounts of gamma-rays and spins at a rate of 390 times per second. Its light-weight companion is a compact object with at least 8 times the mass of Jupiter and is comprised mainly of helium. The companion is believed to be the compact remnant of a star that was cannibalized by the pulsar. Being at a distance of only 1.4 times the Earth-Moon separation distance from the pulsar, the companion whizzes around the pulsar once every 93 minutes. In fact, the companion swings around the pulsar at a terrific speed of 2.8 million km/h.

At such a close proximity to the energetic pulsar, the companion is being blasted at point-blank range by intense gamma radiation and is literally evaporating away. One can imagine the “dayside” of the companion being superheated until it shines blue-white. The cloud of vaporized material emanating from the companion absorbs so much radio wave emissions from the pulsar that the pulsar is invisible to radio telescopes. PSR J1311-3430 is a type of pulsar known as a “black widow,” because like the black widow spider, which kills its partner after mating, the pulsar is expected to eventually vaporize its companion completely.

Romani et al. (2013), “PSR J1311-3430: A Heavyweight Neutron Star with a Flyweight Helium Companion”, arXiv:1210.6884 [astro-ph.HE]