This composite image made in 1994–97 shows rings of gas expanding from the dying star. The exploding star released a burst of neutrinos observed on Earth. In 1987, the most spectacular supernova seen in four centuries appeared in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. The physicist Enrico Fermi named Pauli’s particle the neutrino, meaning “little neutral one” in Italian. Pauli gained confidence and published his idea. Then in 1932, James Chadwick discovered the neutron, a particle with nearly the same mass as the proton but no electric charge. He understood that a scientific theory is almost worthless unless it can be tested by observation or experiment, and he was concerned that such particles could never be detected. Pauli suggested this in a letter to his colleagues but didn’t publish it. To agree with the observations, this particle had to be electrically neutral, possess practically zero mass, and move at the speed of light. The Austrian physicist Wolfgang Pauli, so convinced of the conservation principle, made a daring intellectual leap by proposing that an unknown particle carries off the missing energy. This appeared to violate the conservation of energy, a fundamental principle of physics which says that energy is neither created nor destroyed. Experiments showed that the total energy of the nucleus plus the ejected electron after the decay was less than the energy of the initial nucleus. Neutrinos entered theoretical physics in 1930 as a way to understand beta decay, the process by which a radioactive atomic nucleus spits out an electron. Like visible light from stars, radio waves from galaxies, and X-rays from matter spiraling down black holes, neutrinos can also reveal something of the cosmos. In fact, during the next second, trillions of neutrinos from cosmic sources will pass through your body with no effect. Subatomic particles called neutrinos permeate the universe. However, light is not the only carrier of information across space. The astronomer does not even have to be anywhere near the telescope, which could, for example, be in space.Ī wide range of modern detectors can “see” not only visible light from celestial objects but also every other kind of light in the electromagnetic spectrum, from radio waves to gamma rays, all invisible to human eyes. Instead they look at computer monitors while directing the operation of sensitive electronic light detectors attached to telescopes. While this sort of thing was, in fact, common a generation ago, astronomers today rarely “look” through telescopes. Photo courtesy of the ICRR (Institute of Cosmic Ray Research), The University of Tokyo. Technicians on a raft check the photodetectors (far right). Neutrinos from space interact with the water and produce flashes of blue light. The Super-Kamiokande neutrino observatory uses 50,000 tons of pure water surrounded by 11,200 sensitive light detectors 1 kilometer below ground in Japan.
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