The world’s largest observatory captures messengers from afar
To detect the very smallest particles arriving from outer space, you need to build the world’s largest observatory in Antarctica.
That insight earned Francis Halzen this year’s Nobel Prize in Physics.
Neutrinos are elementary particles that carry no electric charge but can carry large amounts of energy. Because of their properties, they are extremely difficult to capture or stop, and they are everywhere.
‘Every second, 65 billion neutrinos pass through an area the size of a thumbnail. They can travel straight through the Earth without hitting anything that affects them,’ says Maria Sundin, researcher in astrophysics at the University of Gothenburg.
Unaffected particles an advantage
Neutrinos are created when different particles interact with one another. Francis Halzen was interested in studying those produced by high-energy events in space. They are extremely difficult to stop because they have high energy, an extremely small mass and no electric charge – which, in this case, is also an advantage for astronomers.
‘The particles’ motion is not affected by other objects, which means we know where they come from. They point us in the direction of where a star exploded or a black hole formed, and the information reaches us unaltered. This tells us where to direct our observations of the night sky using other measurement methods,’ says Maria Sundin.
Francis Halzen calculated that he would need a volume of at least one cubic kilometre (1,000 × 1,000 × 1,000 metres), equipped with particle detectors, to detect the traces left by the occasional neutrino that, despite its energy, had interacted with its surroundings.
IceCube a cool observatory
The requirements for a neutrino observatory led him to choose Antarctica. The ice is kilometres thick and stable, and there is no surrounding interference from human activity. Francis Halzen’s research team drilled 60 holes in the ice, in some cases reaching depths of 2,450 metres. A detector was suspended in each hole to detect particles with energies on the teraelectronvolt scale, 10¹² electronvolts. An electronvolt (eV) is the amount of energy gained by an electron when it is accelerated through an electric potential difference of one volt. In 2011, the facility was completed and named the IceCube Neutrino Observatory.
‘The first time they published a study of an observation was in 2013, so this is still a relatively new field of research. What their observations may ultimately lead to remains to be seen,’ says Maria Sundin.
In total, the Nobel laureate counts 450 researchers as part of his team. At IceCube, they have to make do with an average of one detected particle per day.