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Heart of supernova reveals hints of hidden pulsar

Neutron clue Astronomers have detected the first signs of the birth of a neutron star at the heart of a supernova remnant.

Supernova 1987A suddenly exploded on 23 February 1987 on the edge of a nearby dwarf galaxy called the Large Magellanic Cloud 168,000 light years away.

The event, which was visible with the unaided eye, was one of the nearest core collapse supernovae of modern times, giving scientists an opportunity to study the cataclysmic blast in unprecedented detail.

The new research, reported in the Astrophysical Journal, has detected signs of what could be a pulsar wind nebula driven by a spinning neutron star or pulsar.

"We've never seen a neutron star so young," says the study's lead author Dr Giovanna Zanardo of the University of Western Australia node of the International Centre for Radio Astronomy Research.

"If this is a pulsar, then a quarter-century-old mystery about what supernova 1987A created, will have been solved.

"The beauty about the star that exploded to create supernova 1987A is that it was a blue supergiant about 20 times the mass of our Sun, so it could have produced either a neutron star or a black hole."

Stars greater than 20 solar masses are thought to produce black holes, while those smaller leave behind neutron stars.

Neutron stars are the extremely dense cores of stars much more massive than the Sun that have blown off their outer layers in supernovae explosions bright enough to briefly outshine an entire galaxy.

A neutron star is called a pulsar when its rotation can be detected by astronomers.

Seeing through the dust

Zanardo and colleagues used the Australia Telescope Compact Array at Narrabri, and the Atacama Large millimeter-submillimeter Array in Chile, to observe the remnant of supernova 1987A at wavelengths spanning radio and far infrared frequencies.

"This allowed us to distinguish radiation emitted by the supernova's expanding shock wave, from the radiation caused by dust forming in the inner regions of the remnant," says Zanardo.

"We can peek through the bulk of debris ejected by the supernova to find what's hiding underneath for signs of a new object formed when the star's core collapsed.

"We're sure there's a neutron star there, hidden under the dust."

Zanardo describes it as undertaking a forensic investigation into the death of a star.

"Final confirmation won't come until we detect the pulsar signal from the neutron star, which is usually done with a telescope like Parkes," says Zanardo.

"A neutron star is so compact that it usually starts to spin quite early, sending pulse emissions to Earth. We want to catch those pulses to confirm the discovery."

At this point, Zanardo and colleagues are seeing a diffused emission.

"It's a faint glow which is going through the dust and material in the centre of the supernova, so we're really close," says Zanardo.