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Stellar Tease

March 20, 2013

A giant star that teased astronomers into thinking it had exploded three years ago finally blasted itself to bits last year.

When the star produced a mammoth eruption in 2009, astronomers designated it as Supernova 2009ip. Within days, though, they had second thoughts. The explosion faded too quickly for a true supernova, and the material it blasted into space was moving too slowly. Astronomers realized the star had duped them.

After a similar outburst a year later, 2009ip staged a third eruption last July. It remained bright for weeks, and the ejected material was traveling at a few percent of the speed of light. In other words, this outburst really was a supernova.

Pictures snapped over a period of about 10 years before the final explosion revealed that the star was a luminous blue variable. Such stars are dozens of times as massive as the Sun and a million times brighter. 2009ip is the first confirmed instance of such a star exploding as a supernova.

Astronomers aren’t sure what caused the earlier outbursts. One possibility is a reduction in the radiation pressure in the star’s core, which keeps the core from collapsing. Another is the ignition of nuclear reactions in different layers around the core. Either process could mimic a supernova - and fool astronomers into thinking the star had blasted itself to bits.

The blast probably left behind a tiny, crushed core known as a neutron star. More about neutron stars tomorrow.


Script by Damond Benningfield, Copyright 2013

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