SUPERNOVAE are among the universe鈥檚 most spectacular events, and until now they have always taken astronomers by surprise. But later this year, a detector will begin scouring the skies to alert astronomers hours before the light from a supernova in our galaxy reaches Earth, allowing them to witness, for the first time, the birth of a supernova.
When a massive star collapses at the end of its life, it releases a tremendous blast of energy that blows its envelope into interstellar space. Less than one per cent of this energy is in the form of visible light, and the photons can take hours or even days to work their way out of the star鈥檚 dense core. This means the collapse will be well under way by the time astronomers get any visible indication of the supernova.
But the rest of the energy is released in the form neutrinos, which interact weakly with ordinary matter and so shoot out of the star unhindered. They therefore provide an immediate signal that a collapse is under way. 鈥淣eutrinos are the only way to know ahead of time that a supernova is about to appear,鈥� says Kate Scholberg, a physicist at the Massachusetts Institute of Technology.
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Before a supernova in the nearby Large Magellanic Cloud was observed in 1987, several detectors picked up its neutrinos. At the time, there was nothing in place to quickly link these signals to the supernova and astronomers missed a rare opportunity to observe the early stages of a supernova in detail. So Scholberg and her colleagues have now set up a system called the Supernova Early Warning Network (SNEWS) to monitor data from three neutrino detectors: the Super-Kamiokande detector in Japan, the Sudbury Neutrino Observatory in Canada and the Large Volume Detector in Italy.
When the three labs detect neutrinos from a supernova within 10 seconds of each other, a human operator is alerted to check the data. This check can take up to an hour, Scholberg says. In the next few months an automated system will start working out the supernova鈥檚 approximate position in the sky and send out alerts less than 10 minutes after the first neutrinos are received ().
The alerts will be sent out as emails to thousands of professional and amateur astronomers around the world, including those operating the Hubble Space Telescope. Anyone can sign up at . 鈥淪NEWS is a great opportunity for amateurs to make a contribution,鈥� Scholberg says.
John Bahcall, a neutrino expert at the Institute for Advanced Study in Princeton, New Jersey, says the opportunity to observe a supernova in action is a once-in-a-lifetime opportunity. 鈥淚n fact, the information may be more valuable than 鈥榦nce in a lifetime鈥� since the next nearby supernova could be more than a 100 years in the future. Or, it could occur tomorrow,鈥� he says. 鈥淭he SNEWS is keeping us ready.鈥�
The system will help astronomers study the effects of a nearby companion star on the supernova, or look for the flashes of ultraviolet light and X-rays predicted by theory.
In the future, the early warning system could include gravitational wave detectors. Though no gravity waves have yet been observed, the hope is that detectors such as LIGO in the US may be able to pick up gravity waves from certain types of supernovae even before the neutrinos arrive on Earth.