Supernovas & neutrinos: From tiny to vast
"It won't work, Jose." said Gino Segrè as he looked down while tying his shoe laces. Segrè, relative of the well known scientist who had helped design the first atomic bomb, was speaking to Jose F. Nieves, a physics professor at the University of Puerto Rico, about the astronomical implications of Nieves's work on neutrinos. A few weeks later in 1996, Segrè sent a very different message by email: "It works." Supernovas, and more specifically the pulsars they often turn into, had been elucidated.
Neutrinos and supernovas could not be more different. One is a particle with characteristics so peculiar, that it is nearly invisible to the most sophisticated modern equipment. Even its 'detection' is never direct, but rather is indirectly seen by the effects its antiparticle leaves behind. Since they are nearly massless and have no charge, they race through the universe unimpeded. Every second 60 billion neutrinos pass through every square centimeter of your body, most of them originating in the sun.
Supernovas are...well...supernovas. They are stars which, nearing their life's end, are reborn by exploding with such power that they attain the visible space of an entire galaxy. When first detected by modern telescopes in 1885, the idea that such brightness could be caused by a single star was so preposterous that it was initially rejected. After supernovas explode, they can turn into a neutron star that rotates so quickly it emits radio signals on a regular split-second basis, hence the term 'pulsar'. Another well-known, but then unexplained, feature of pulsars was that they moved in odd directions to most stars, as if they had been kicked by a celestial soccer player. Prof. Segrè showed that Nieves's conclusions could be used to account for this odd property.
Prof. Nieves began work with neutrinos in 1981, long before it was fashionable to do so. After obtaining his first degrees from the University of Puerto Rico, he focused on the physics of weak interactions for his University of Pennsylvania doctorate. Yet his interests were further defined while working as a postdoctoral fellow at Carnegie-Mellon. He became interested in the electromagnetic influence of a particle which seemed to have none.
Nieves first discovered that these illusive particles were not as intangible as they might seem. Although they do not have electrical charge, they were affected by magnetic fields. In a 1982 paper which appeared in the renown Physical Review, he showed that although Majorana neutrinos have no such properties, Dirac neutrinos did. In curious scientific terms, the Dirac's magnetic moment was non zero. But this work considered neutrinos in empty space; a supernova in 1987, shifted the course of his research once again.
Supernovas are so rare, that when one exploded in 1987, astronomers went bizerk; it was an experiment found in nature which no human laboratory could ever reproduce. Huge underground detectors in Japan and the United States registered 100-fold spikes in neutrinos. This is significant when one considers that such instruments can only identify one out of billions passing by. A link between the most massive and the most insignificant had been established. Nieves quickly got back to work soon thereafter.
Two years later, working with the Indian physicist Palash B. Pal, Nieves expanded his 1981 article by describing the properties of neutrinos in a medium such as the hot plasma of a supernova. They discovered mathematically that neutrinos change in this new environment. Majorana neutrinos now acquired magnetic properties. During a series of papers in 1997, the two scientists fully documented the entire array of electromagnetic interactions between neutrinos and the surrounding particles.
The cumulative efforts of Nieves, Pal, and Segrè amounted to the following discovery about pulsars. When a supernova explodes, the vast majority of the energy created (99%) is released by neutrinos in a rather complex process that takes only seconds to occur. When the neutrinos escape the supernova, some heat the surrounding gasses, which in turn create more neutrinos in a cascading effect similar to that found in atomic bombs. Yet the pulsar does not get its kick from the visible heated gases, as it was once thought, but rather from the invisible neutrinos themselves. Because one percent of these favor a particular direction as a result of their interaction with the magnetic field, they 'kick' the pulsar in its odd direction at 450 km/s.
These discoveries have also pushed Dr. Nieves into the limelight in the world of modern physics. His work has been cited in more than 500 articles and books, and is now a regular part of modern textbooks. This prestige has also helped bring modern physicists from around the world to Puerto Rico via a series of conferences organized by Dr. Nieves. These have included symposiums of high energy physics, particle physics, and cosmology, and have been attended by scientist from prestigious institutions as CERN, Fermilab, Lawrence Berkeley National Laboratory, and others. We might say that Nieves is a "local boy who has done good."
Prof. Nieves is currently organizing another conference to be held in 2003, whose participants will discuss the design of an accelerator dedicated to the study of neutrinos. The accelerator is referred to as a "v factory" ('v' is the Greek symbol used to represent neutrinos).