SUPERNOVAE, which are among the universe鈥檚 most spectacular explosions, could be caused by powerful sound waves.
A massive star detonates as a supernova when the nuclear fuel in its core runs out. The core can no longer withstand gravity and it implodes into a super-dense neutron star. But the next step is a puzzle: how does the implosion turn into an explosion?
Some theorists have suggested that after the neutron star forms, the surrounding stellar matter that continues to rain down on it bounces off the dense surface, and this causes the explosion. Others have postulated that the outer layers of the star are blown away by a burst of neutrinos unleashed as the neutron star forms. Yet computer simulations of both scenarios invariably lead to a disappointing fizzle rather than a bang.
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But when Adam Burrows of the University of Arizona in Tucson and his team simulated the collapse of an 11-solar-mass star, they found that oscillations, or sound waves, were triggered in the turbulent and violently shrinking core. The matter raining down on the neutron star was making it ring like a bell, and the researchers think this booming effect blasts the outer layers into space. 鈥淭he core oscillation acts like a transducer, efficiently converting the gravitational energy of the infalling matter into radiating acoustic power,鈥� says Burrows.
The sound waves persist as long as matter is falling in, so the explosion does not fizzle out in simulations as it seems to for other mechanisms. Also, the sound is preferentially radiated in some directions. 鈥淭his could explain why neutron stars are often observed being kicked out at high velocity from supernova explosions,鈥� Burrows says ().
鈥淭he theory could explain why neutron stars are often observed being kicked out at high velocity from supernova explosions鈥�
鈥淭his is an interesting new mechanism,鈥� says Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics. 鈥淚t remains to be seen how this proposal will survive the test of time.鈥�
Burrows and his team agree that more work is needed to fully understand their mechanism. They also point out that the theory is potentially testable. The sound waves in the ringing neutron star could generate characteristic gravitational waves, or ripples in the fabric of space-time, so they could one day be picked up by gravity-wave detectors such as the LIGO Hanford observatory in Washington state.
