Researchers drilled holes in the ice to a depth of almost 1.5 miles, and lowered 60 basketball-sized detectors called digital optical modules (DOMs) into each of the 86 holes. They then had to pull cables to connect the sensors to IceCube Lab’s servers in order to collect data. | Photo courtesy of the National Science Foundation
With a bit of effort, a negative can sometimes become a positive.
That’s especially true in the sciences. Experiments don’t always work out as planned, or at least as hoped. Errors can creep in despite the best controls. And even when experiments work right, they often simply suggest that the initial idea was wrong, or at least needs to be modified.
Findings that rule out one idea, rather than ruling anything in, are called negative results. They’re an essential part of the scientific process. And, with a bit of effort, they can become positive occurrences.
That was true of recent results from the IceCube Collaboration, to which Lawrence Berkeley National Laboratory is an essential contributor. IceCube, designed to study some of the most powerful phenomena in the universe, is one of the most amazing telescopes ever constructed. For starters, the telescope is buried in the ice at the South Pole, a full cubic kilometer in size.
Researchers drilled holes in the ice to a depth of almost 1.5 miles, and lowered 60 basketball-sized detectors called digital optical modules (DOMs) into each of the 86 holes. At that depth, pressure pushes all the bubbles out of the ice, so it's perfectly clear. It's also very dark, so the DOMs can detect the ghostly particles known as neutrinos.
Neutrinos come from a variety of sources, but they’re typically created in big bangs: The big one that kicked off the universe, the fusion fires of the sun, and the great star explosions known as supernovae.
The highest-energy neutrinos were thought to be produced in titanic explosions – the collapse of super-massive stars or the collisions of black holes with other black holes or neutron stars. Those super explosions are known as gamma raybursts, and were believed to create rare, ultra-high-energy cosmic rays consisting of particles that pack far more punch than an earthly accelerator.
Scientists reasoned that if gamma ray bursts produce the highest-energy cosmic rays, they should also produce high-energy neutrinos, which IceCube could pick up. However, after an exhaustive study (published in the April 19th issue of Nature), they found . . . nothing.
That’s despite having some of the best detectors available, which were designed and developed by Berkeley Lab. Its 5,160 digital optical modules form the “mirror” of the IceCube telescope. They’re strong enough to stand Antarctica’s ice, and yet sensitive enough to detect the tell-tale signs of high-energy neutrinos. Berkeley Lab’s National Energy Research Scientific Computing Center also contributes its supercomputing power to filtering the signals and analyzing the data from IceCube.
IceCube collaborators are still striving to understand the actual source of ultra-high-energy cosmic rays. Since they don’t appear to come from gamma ray bursts, they could come from active galactic nuclei (AGNs), the supermassive black holes at the center of active (extremely bright) galaxies. If the evidence suggests that AGNs aren’t the source either, then scientists will come up with a few new ideas.
That quest for understanding animates the efforts of the National Labs. It’s a search that never ends, even at the frozen ends of the earth. Even there, as part of the IceCube collaboration, scientists are striving to see further, to open new possibilities, to turn negative findings into positive results.
The IceCube Media Gallery has photos of the DOMs, drilling, and the Antarctican landscape surrounding their South Pole laboratory.