Supernova Afterlife

Inner light. Radio observations (bottom: high frequency at right) reveal a black hole or neutron star at the heart of supernova 1986J.

When a bloated, aging star collapses under its own weight, the implosion is so powerful the outer shell of the star explodes in a blinding flash known as a supernova. Those fireworks have been well-studied, but the quieter fate of the star's core is still mysterious. Astrophysicists assumed the core of the old star lives on, either as a neutron star or a black hole, but no one had ever seen this taking place. Now a group of researchers claims to have done just that, by spying a neutron star in its infancy.

Although supernovas aren't rare, astronomers haven't been able to prove the connection between a nova and a neutron star or black hole. Many supernovas are too far away, or not bright enough, for astronomers to distinguish between the remnants of the gas shell and what's inside it. And black holes are difficult to see under the best of circumstances. Until now, the best proof that old post-nova stars turn into superdense objects was the Crab nebula, the remains of a supernova observed by Chinese astronomers in 1054. A pulsing neutron star, or pulsar, was later discovered right where the old core of the star should be.

In a paper published online 10 June in Science, Michael Bietenholz and colleagues at the University of Toronto report an even more tantalizing find: a newborn neutron star in the center of supernova 1986J. They looked at the supernova, which exploded in 1986, in three radio frequencies. At the highest of these frequencies, 15 Ghz, they could see a clearly defined radio source, which they suspect is a neutron star, smack dab in the center of the nebulous gas leftover from the supernova. The neutron star is less than 20 years old, incredibly young by star standards, and could be the perfect window into the early evolution of ultradense post-nova star cores.

"It's gratifying to finally see a compact object be found," where we know it should be, says Roger Chevalier, an astrophysicist at University of Virginia in Charlottesville. Although the radio observations can't distinguish between a neutron star or a black hole, future optical and x-ray observations of 1986J should nail it down, he says.

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