Even Wolfgang Pauli, the first scientist to think of neutrinos, had his doubts. He reportedly wrote in a letter, “I have done a terrible thing. I have invented a particle that cannot be detected.”
Since Pauli’s time, scientists have found ways to build neutrino detectors and search for the strange particle. Halzen is in on the hunt. He is leading a team of scientists building a neutrino detector at the bottom of the world, not far from the South Pole. The machine, called IceCube, is about half done.
When complete, IceCube will be the largest scientific instrument in the world, the size of about 1,000 Empire State Buildings. Isn’t it strange that to find the smallest thing, scientists will have to use the biggest machine?
Why bother looking for neutrinos? These tiny particles can tell us about black holes and exploding stars. Scientists at the South Pole believe IceCube might also pull back the curtain on outer space, revealing strange new things that we can’t yet even imagine.
Tiny ghosts from outer space
Neutrinos travel in straight lines, passing right through almost every kind of matter without changing direction. That means “we can use these particles to bring us information from regions of space that other things can’t,” explains Doug Cowen, an IceCube scientist at Pennsylvania State University in University Park.
Take the area around black holes, for example. Believed to exist at the core of most galaxies, black holes are ultra-compact objects with a mass millions to billions of times that of our sun. They’re difficult to study because they absorb most kinds of radiation, including visible light. If light from a black hole doesn’t get to Earth, then we can’t “see” it.
Scientists suspect that when supermassive black holes “eat” some nearby matter, powerful jets of energy escape into space. The jets can quickly create a stream of high-energy neutrinos, which travel in an everlasting straight beam through space. Other particles might also escape a black hole, but they can be quickly absorbed by dust or deflected by electromagnetic fields.
When an instrument like IceCube detects high-energy neutrinos, scientists can trace the straight line backwards to pinpoint its parent black hole. The neutrinos’ path through the detector will serve, like an arrow, to point at the black hole. Once astronomers know where to look, they can then use other instruments to study the black hole.