1. Astro Physics

Category Archives: Astro Physics

Imaging the spotty surface of Betelgeuse in the H band

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Authors: X. Haubois, G. Perrin, S. Lacour, T. Verhoelst, S. Meimon, L. Mugnier, E. Thiébaut, J. P. Berger, S. T. Ridgway, J. D. Monnier, R. Millan-Gabet and W. Traub
A&A 508, 923 (2009) Received 18 July 2009 / Accepted 7 October 2009
Keywords: convection, techniques: interferometric, stars: fundamental parameters, infrared: stars, stars: individual: Betelgeuse

Revealing the sub-AU asymmetries of the inner dust rim in the disk around the Herbig Ae star R Coronae Austrinae

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Authors: S. Kraus, K.-H. Hofmann, F. Malbet, A. Meilland, A. Natta, D. Schertl, P. Stee and G. Weigelt
A&A 508, 787 (2009) Received 26 July 2009 / Accepted 28 October 2009
Keywords: stars: pre-main-sequence, circumstellar matter, accretion, accretion disks, planetary systems: protoplanetary disks, planetary systems: formation, techniques: interferometric

Scientific Pig-Out

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The American Physical Society is pleased with the bit
of pork congress is giving the National Science Foundation
and the National Aeronautic and Space Administration in the
American Recovery and Reinvestment Act of 2009 that just passed
the U.S. House of Representatives.  I explain why I believe
their joy is misplaced, and why astronomy and astrophysics may
see a long-term decline in funding because of increased
government spending.

The Neutrino Cooling of Degenerate Dwarfs

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The principal way that a degenerate dwarf cools
is through the emission of neutrinos.  Unlike the
main-sequence stars, which generate neutrinos as part
of their thermonuclear generation of power, degenerate
dwarfs generate neutrinos from photons.  This process
allows degenerate stars to radiate away all of the energy
in their cores, giving them an inverted temperature structure
of a cold core surrounded by a hot outer layer.

The Neutrino Cooling of Neutron Stars

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Neutron stars are strong neutrinos emitters.  The
power radiated by a neutron star as neutrinos far outstrips
the power radiated as x-rays from the photosphere.  Three
processes are responsible for generating the neutrinos: the
direct Urca process, the modified Urca process, and the
neutrino bremsstrahlung process.  The first process is rapid;
it  operates at the cores of the most massive neutron
stars.  The remaining-two processes, which operate throughout
a neutrons star, cool the neutron star more slowly.  The
neutrino emission cools a neutron star in only 100,000 years.

Overview of Supernovae

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Theorists divide supernovae into two types:
core-collapse supernovae and thermonuclear detonation
supernovae.  The first type occurs when a massive star
exhausts its thermonuclear fuel.  The second type occurs
when a white dwarf experiences a thermonuclear runaway
after becoming gravitationally unstable.  These rare but
intense explosions can be seen across the universe.  They
are responsible for all of the heavy elements in the universe,
and are therefore necessary for human life.

Energetics of Thermonuclear Supernovae

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The thermonuclear energy locked inside a white dwarf
is sufficient to blow the star apart.  In particular, white
dwarfs composed of carbon and oxygen, which are more common and
contain more thermonuclear energy than those composed of oxygen,
neon, and magnesium, can release up to 0.1% of the star's rest
mass energy as the carbon and oxygen are converted into
an unstable isotope of nickel.  The energy released in the
explosion goes into expanding the debris from the white dwarf
to velocities approaching 10% of the speed of light.  The power
we see radiated from a thermonuclear supernovae comes from the
decay of radioactive nickel to iron.  The light we see from
a thermonuclear supernovae is about 10% of the energy released
in the explosion, or 0.01% of the white dwarf's rest mass energy.


  1. Astro Physics