Meet two possible visitors from another galaxy, Bert and Ernie. You might have missed their respective arrivals in August 2011 and January 2012, just as, right now you’re missing their friends and distant relations, even though billions of them are passing through every square centimeter of your body every second.
That’s because Bert and Ernie are deeply weird subatomic particles called neutrinos (and if we don’t stop anthropomorphizing them right now a howling mob of physicists will throw us in a box with Schrödinger’s cat).
If neutrinos can pass through us unnoticed, how do we detect them? It’s a matter of finding a very dark place free from other forms of radiation. Because very occasionally, neutrinos will collide with water molecules and release a faint blue flash of Cherenkov radiation (fun fact: Cherenkov radiation is why water-cooled nuclear reactors glow blue). Unused mine shafts and giant tanks of water ringed with sensors have been used to detect these collisions before.
And then there’s IceCube. It’s an entire cubic kilometer in size, bored into the ice of the South Pole in 86 shafts, down which run 86 strings of light detectors, some 5,160 detectors in all. In fact, IceCube is more of a hexagonal tube pointed straight down and it is, in fact, a telescope. Optical telescopes detect photons of light, radio telescopes detect radio waves and IceCube detects the ghostly flashes of neutrinos, which, come to think it, means it’s an optical telescope, too, but you get the idea.
Which brings us back to Bert and Ernie. And, frankly, you’d better get it from an expert. Spencer Klein is one of the IceCube team, a senior scientist at the Lawrence Berkeley National Lab, a research physicist on the Berkeley campus, and one of 16 Berkeley authors on an IceCube paper with 284 authors from 41 institutions. So I asked Klein about Bert and Ernie and said, “Go ahead: Speak to me like I’m a dummy.”
“Bert and Ernie are these two neutrinos that we’ve observed in Ice Cube. We’re very clear that they’re neutrinos, we’ve measured their energies, they’re both over 1 PeV [peta-electronvolt],” he said. “Sort of for comparison, house current is 120 volts, so if you accelerated an electron using house current this would be 10 trillion times as energetic as an electron you might get from house current. What we don’t know is where they’ve come from.”
Still, the high energy of these two neutrinos means that they could well be extraterrestrial and not created by cosmic rays hitting the earth’s atmosphere. Bert and Ernie could even be from a black hole at the center of a galaxy not our own. Maybe. But we don’t know yet. We need to observe more neutrino strikes to develop a fuller idea of what’s going on, and that’s what IceCube is going to be doing for the next ten years or so. Bert and Ernie are just the beginning of what it will find.
Oh, one last question for Klein: Why do the neutrinos have Muppet names?
There’s a brief pause and possibly a sigh on the other end of the line.
“Somebody started giving neutrino events cute names, and it started with Bert and Ernie,” Klein says. “There’s nothing deep there.”