All posts by Callum Tyndall

Scientists find no evidence of elusive sterile neutrino

After analysing thousands of neutrinos in the IceCube Neutrino Observatory at the South Pole, researchers from the Niels Bohr Institute have now confirmed that there is no evidence for the existence of sterile neutrinos.

Neutrinos, also known as ghost particles, are some of the most abundant in the universe. and potentially hold answers to some of the more mysterious universal phenomena. Able to travel through virtually anything, neutrinos have thus far been identified as falling into three types: muon, electron and tau. The fourth type, the sterile neutrino, was thought to potentially explain phenomena like dark matter.

There have been previous indications of the sterile neutrino in experiments from across the world, prompting great interest from the research community, particular as sterile neutrinos may have different properties, such as interacting only be means of gravity.

Niels Bohr Institute PhD student Morten Medici poses in front of the South Pole-based IceCube Lab, where the research was conducted. Image courtesy of Morten Medici

Niels Bohr Institute PhD student Morten Medici poses in front of the South Pole-based IceCube Lab, where the research was conducted. Image courtesy of Morten Medici

“One or more types of sterile neutrinos could help solve a number of mysteries, such as why there is more matter than antimatter in the universe,” explained Jason Koskinen, assistant professor at the Niels Bohr Institute at the University of Copenhagen and group leader in the IceCube research group at the Niels Bohr Institute and team chairman of the IceCube international research team on neutrino oscillations.

“A sterile neutrino could provide an explanation for this imbalance, which currently cannot be explained by the three known neutrinos. A sterile neutrino with gravity could also shed light on the mysterious dark matter.”

When high energy protons hit Earth’s atmosphere they create a shower of particles that includes neutrinos. Due to their unique properties, the neutrinos then pass straight through the Earth while the other particles collide with it.

However, a minute proportion of those forming over the North Pole will end up hitting the ice at the South Pole, where they can be detected by the IceCube detector, a setup consisting of 5,160 light sensors that are frozen in Antarctica’s ice.

An image of the IceCube Neutrino Observatory overlaid with a plot of neutrino transformations, including the hypothetical fourth neutrino, shown in red. In reality, the researchers found no evidence for its existence, which should have been unearthed in this research if it were to exist. Image courtesy of IceCube Collaboration

An image of the IceCube Neutrino Observatory overlaid with a plot of neutrino transformations, including the hypothetical fourth neutrino, shown in red. In reality, the researchers found no evidence for its existence, which should have been unearthed in this research if it were to exist. Image courtesy of IceCube Collaboration

The operating theory so far has been that the sterile neutrino could be formed during the fluctuations that cause neutrinos to shift between muon, electron and tau forms. These quantum changes occur during the particles’ travel and, even if there were to be a fourth version, should all be detectable by the IceCube.

“We have analysed hundreds of thousands of neutrinos, which after having passed through the Earth from the Northern Hemisphere have hit the ice on the South Pole, where the collisions have been recorded in the IceCube detector,” explains Koskinen.

“We know of three neutrino types and our international team of researchers has been looking for signals from a fourth neutrino type, the so-called sterile neutrinos. For years, there has been a global mystery about the existence of a sterile neutrino with a mass of about 1 eV. If it existed, it would produce a clear signal at a certain energy interval, but we have not seen a single signal that could come from such a sterile neutrino.”

Spark of inspiration: NASA’s move towards electric aviation

In a move towards a ‘greener’ aviation industry, NASA has selected five technology concepts for a two-year study that may well transform the industry in the next decade. Broadly aimed at reducing aircraft fuel use and emissions, three of the five topics selected are specifically aimed at the development of electrically-propelled aircraft.

The concepts, which were selected under NASA’s Transformative Aeronautics Concepts Program, are: alternative fuel cells; using 3D printing to increase electric motor output; the use of lithium-air batteries for energy storage; new mechanisms for changing the shape of an aircraft wing in flight and the use of a lightweight material called aerogel in the design and development of aircraft antenna.

These five will join the six selected last year in addressing NASA’s goals to cut fuel use by half, lower harmful emissions by 75%, and significantly reduce aircraft noise.

The focus towards electric aircraft obviously plays a significant role in achieving these aims and represents the potential for a huge shift within the field of aviation, mirroring the ecological intentions of companies like Tesla in the automotive field.

“There definitely was an emphasis in our selections on bringing forward activities that addressed a NASA aeronautics goal to reduce the carbon footprint of aviation during the 21st century,” said Doug Rohn, NASA’s manager for the Transformative Aeronautics Concepts Program within the agency’s Aeronautics Research Mission Directorate.

While all of the concepts put forward will contribute to reducing the environmental impact of aircraft, the wing mechanisms and antenna serve more as functional design improvements than the innovation of the other three concepts.

This may in fact make them more plausible for successful implementation, but it is to the electric aircraft we should look for the future.

Images courtesy of NASA

Images courtesy of NASA

The importance of the research being explored holds further value due to NASA’s own mandate that: “each study was required to be multidisciplinary, involve multiple centers, directly relate to addressing one or more of NASA aeronautics strategic research goals, and do all of this in a way that is transformative in pushing the state-of-the-art in aviation.”

The promise of multidisciplinary research is what elevates the programme, in that the concepts being explored may well hold the potential to transform industries beyond that of aviation. The lithium oxygen batteries alone are hugely important, given that they have the highest theoretical energy storage capacity of any battery technology.

The concepts are certainly ripe with the capability to change the field but their success is far from guaranteed. That said, the fact that they are being studied at all can be seen as very important. While these may fail, they may lead to further discovery and innovation in the future.

“Is failure an option? It depends on your definition of failure,” Rohn said. “We’re going to ask the questions and see if these ideas are feasible or not. A successful feasibility assessment may determine the concept won’t work.”