Neutrinos and SN1987A

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Neutrinos and SN1987A

• Brent Tunis

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What exactly are Neutrinos?

• Neutrinos were formally discovered by Enrico
  Fermi in 1934 when he realized that, in order to
  maintain the conservation of momentum, there had
  to be another particle that was involved in the
  transformation of a neutron into either a proton
  or an electron
• Neutrinos are very weakly interacting,
  electrically neutral particles that are involved
  in nuclear interactions where protons are changed
  into neutrons or vice versa, and in other
  reactions as well

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The Larger Significance of Neutrinos

• Neutrinos were once thought to be massless, but
  they are now known to have a very small mass of
  only about 0.5 to 5 billionths that of a proton
• Even though small in size, it is believed that
  neutrinos were produced and released into the
  universe, as a result of the Big Bang, in numbers
  comparable to the amount of photons released
• Such a large amount of neutrinos means that they
  could contribute significantly to the overall
  matter of the universe

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Neutrino Experiments

• Neutrinos are extremely hard to find as they are
  so small and can travel through almost everything
  without interaction. It was not until the 60s
  that scientists first to began to detect them.
• The Homestake experiment was one of the first
  that successfully studied neutrinos that were
  emitted from the fusion process in the core of
  the Sun and subsequently made their way through
  Earth.
• It was scientifically proven, however, that this
  experiment was only observing about a third of
  the neutrinos that it should be recognizing.
  This led scientists to conclude that the electron
  neutrinos that were being emitted from the Sun
  were transforming into tau and muon neutrinos
  (less abundant known versions that the Homestake
  experiment was not designed to detect). This was
  a phenomenon dubbed neutrino oscillation and it
  meant that neutrinos could not be massless
  (complicated equations prove that oscillation is
  not possible without some mass).

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Supernova 1987 A

• On February 23, 1987, a large and unusual burst
  of neutrinos was detected over a 13 second
  period. They came from an explosion in the Large
  Magellanic Cloud, a nearby dwarf irregular
  galaxy. They sped through the Universe and
  passed through Earth as a result of a supernova
  that was spotted 20 hours later by telescope
  (because although photons and neutrinos travel at
  relatively similar speeds, photons are not
  released until a shock wave reaches the surface
  of a star). The detection of a large amount of
  neutrinos from the core collapse of a star
  confirmed theories both about neutrinos and
  supernovae.
• If neutrinos were massless they would necessarily
  all travel at the speed of light and arrive at
  the same time this was not the case with the
  observed 13 second interval. It was estimated
  from the blast that neutrinos may have a mass
  less than 17 billionths that of a proton and that
  although they may be numerous in the universe,
  they are less massive than the mass required to
  close the universe for Hubble constants greater
  than 50kms-1Mpc-1.

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More Information about Supernova 1987A

• It was specifically in the nearby Tarantula
  Nebula
• It was discovered by Ian Shelton of the
  University of Toronto at Las Campanas
  Observatory, Chile.
• It was originally thought that supernovae type II
  only came from red supergiants but it was a blue
  supergiant. This meant it was roughly 20 times
  smaller than a red supergiant but had a higher
  surface temperature. This helps explain why it
  was not as bright as other supernovae.
• It was the closest supernova since SN 1604 (which
  was observed in the year 1604 and took place in
  the Milky Way itself) and was about 50
  kiloparsecs or 164,000 light-years away.

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Dark Matter

• Since the discovery of Neutrinos and the
  suggestion that they in fact have small, but
  overall significant masses, it has been suggested
  that they are in fact one of the elements of the
  Universes dark matter (called so because it
  makes up most of the matter in the universe, but
  emits little or no light and is near impossible
  to see). Given the extremely small recorded size
  of neutrinos it is now believed that they cannot
  alone make up the bulk of the Universes dark
  matter.
• Neutrinos are classified as hot dark matter
  because the term hot refers to the high speeds at
  which they move throughout the Universe. It is
  this speed that helps scientists determine how
  neutrinos create structure in the Universe as
  they begin to clump gravitationally.

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Works Cited

• Hawley Holcomb. The Foundations of Modern
  Cosmology
• http//www.astro.ucla.edu/wright/neutrinos.html
• http//zebu.uoregon.edu/soper/StarDeath/sn1987a.h
  tml
• http//en.wikipedia.org/wiki/Supernova_1987a
• http//en.wikipedia.org/wiki/Neutrinos