The fastest object in the Universe
What is the fastest moving thing in the universe, other
than light or other types of electromagnetic radiation? I've always
supposed that it would be the surface of some fast spinning Quasar, but I'm not
sure. Richard, Dayton, Ohio
Pulsars are certainly the fastest spinning star. Some spin so fast that a
spot on their equator goes about 50 000 km/s, which is about 20% of light speed.
Probably the fastest moving thing known in the Universe is a
neutrino (a fundamental particle akin to an electron, but much, much lighter).
At first, we weren't even sure neutrinos have mass, but now "the experimental
evidence is definitive that they do," emails physicist
Erik Ramberg of Fermilab. Ramberg tells the story:
The first evidence came from Ray Davis' underground experiment in South
Dakota in the Homestake mine, looking at neutrinos coming from the Sun. Now
that was a classic iconoclastic experiment! In the early 1970's, Davis
struggled making incredibly delicate measurements that could measure a single
radioactive atom in a vat of 100,000 gallons of cleaning fluid. He
succeeded in extracting a few atoms of argon from the tank. The argon was
produced by solar neutrinos, which demonstrated the Sun does indeed produce
neutrinos, but only a third the number expected. Why only a third?
 Supernova 1987A. Most of the energy produced in supernovas is radiated away in the form of an immense burst of neutrinos. The first
experimental evidence of this phenomenon came in the year 1987, when neutrinos
from supernova 1987A were detected. Photo courtesy of NASA and the
European Space Agency.
But do they have mass?
There were other supporting experiments, but most people regard the 1996
Super-Kamiokande's observation of cosmic ray neutrino oscillations to be the
final proof that neutrinos have non-zero mass. Fermilab has recently confirmed
their experiments: Fermilab sees the same oscillations in the laboratory.
Then the Sudbury Neutrino Observatory confirmed that the total number of
neutrinos coming from the Sun was actually right on the prediction. They
oscillate into different species on their way to Earth — thus explaining Ray
Davis' old puzzling result. Only a third of the number reaching Earth
stayed the same species on the way to Earth, but all actually made it to Earth.
Even more important, neutrinos can only change species if they have non-zero
mass. And there you have it.
Ramberg continues the tale: These oscillation observations indicate
that neutrinos have mass, but they only tell us the mass difference
between the species. If that mass difference also indicates the absolute scale
of neutrino masses, which is likely, then they weigh about 100,000 times less
than an electron, which is already a pretty light particle.
Cosmic ray neutrinos are almost certainly the fastest piece of matter in the
Universe.
Further Reading:
Ray
Davis' solar neutrino experiments
The
history of neutrinos, IceCube Neutrino Observatory
Neutrino physics, Science @ Berkeley Labs
(Answered July 14, 2008)
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