Transcript Neutrinos and SN1987A

Neutrinos and SN1987A
Brent Tunis
What exactly are Neutrinos?
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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”
The Larger Significance of Neutrinos
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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
Neutrino Experiments
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Neutrinos are extremely hard to find as they are so small and can
travel through almost everything without interaction. It was not
until the 60’s 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).
Supernova 1987 A
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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.
More Information about Supernova 1987A
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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.
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 Universe’s 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
Universe’s 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.
Works Cited
• Hawley Holcomb. The Foundations of
Modern Cosmology
• http://www.astro.ucla.edu/~wright/neutrino
s.html
• http://zebu.uoregon.edu/~soper/StarDeath/
sn1987a.html
• http://en.wikipedia.org/wiki/Supernova_19
87a
• http://en.wikipedia.org/wiki/Neutrinos