The most energetic supernovae are powered by gravitational potential energy.
Once a massive star consumes all of its thermonuclear fuel, it is unable to support
itself against its own gravity.  The core of such a star collapses to a neutron star.
The birth of a neutron star is heralded by a burst of neutrinos that blows apart
the remainder of the star.  We see this expanding debris as a supernova.

The Large Hadron Collider at CERN, a machine
that accelerates protons to very high energies and then
bangs them together, began operating on September 10, 2008.
Some believe this machine threatens Earth. They need not
worry, because the particle collisions created in this
machine occur daily when cosmic rays strike Earth's
atmosphere. Man can't yet rival nature's extremes.

A core-collapse supernova releases most of its energy as neutrinos.  This
theoretical conclusion is confirmed by a single event, the supernova seen in
the Large Magellanic Cloud in 1987.  Large neutrino detectors buried deep underground
detect cosmic neutrinos by looking for neutrino collisions with electrons.  Three
neutrino detectors saw a handful of these collisions by neutrinos traveling from
the direction of the Large Magellanic Cloud just before a blue supergiant star
in the nearby dwarf galaxy exploded.  The energy carried by these neutrinos
is consistent with the energy generated in the core-collapse of a massive star.

The stars and planets have radii that are set by
the balance of internal pressure against self-gravity.
Because internal pressure has several sources, the stars
and planets fall into several classes, each characterized
by a specific source of pressure.  The consequence is that
the objects of each class obey a unique relationship
between radius and mass.

The Chinese government is investing in
a rocket engine called the Emdrive that generates thrust
with microwaves.  There appears to be a slight problem,
however, with this engine: it violates conservation of
momentum.

Objects supported by electron degeneracy pressure
span a broad range of masses.  The low-mass end of this
range, which is near the mass of Saturn, is set by the
transition from pressure exerted by atoms to pressure
exerted by degenerate electrons.  The high end of this range,
which is 1.4 solar masses, is set by the gravitational
instability that arises when the degenerate electrons have
kinetic energies equal to the electron rest-mass energy.
These limits are given by several fundamental constants
of physics.  Despite the neutron stars being supported
by neutron and proton degeneracy pressure rather than
electron degeneracy pressure, they have an upper mass
similar to that of the degenerate dwarf.

Jupiter and Saturn have a fundamental link
to the degenerate (white) dwarfs and neutron stars: all
of these objects are supported against gravitational
collapse by a pressure generated through the Pauli
exclusion principle of quantum mechanics.  This pressure
is called degeneracy pressure, and it acts through electrons
in planets, brown dwarfs, and degenerate dwarfs, and through
neutrons and protons in neutron stars.  It's existence is
directly linked to existence of chemical elements with
distinctive properties. 

Degeneracy pressure—the pressure caused by the Pauli
exclusion principle of quantum mechanics—is manifested by
four types of astronomical object: the giant gaseous planet,
the brown dwarf, the degenerate dwarf, and the neutron star.
The first-three objects constitute the subclass of degenerate
objects that are supported by electron degeneracy pressure.
The neutron star is the subclass of degenerate objects supported
by neutron and proton degeneracy pressure.  The degenerate
dwarf and the neutron star are two of the three endpoints
of stellar evolution (the third endpoint is the black hole).
Binary star systems containing a degenerate object are the
most brilliant systems in the Galaxy.

The radii of degenerate dwarfs and of neutron stars
are fundamentally linked to the fundamental constants
of physics.  The neutron star is about the size of
a black hole of comparable mass.  The degenerate dwarf,
on the other hand, has a radius that is of order 2,000 times
larger.  This difference in radius is a direct consequence
of the proton being more massive than the electron by this
factor.  The mass of the proton sets the absolute scale
for these objects.  The radius of the neutron star is of
order 15 km, and the radius of the degenerate dwarf
is comparable to Earth's.

Astrophysicists generally assume that the compact
objects at the centers of galaxies are black holes.  Why
couldn't these objects be massive neutron stars or some
other type of degenerate body?  The reason is that under
general relativity and our current understanding of particle
physics, no stable degenerate object can exist with more than
about 5 solar masses.  Gravity would need to deviate from
general relativity for million-solar-mass degenerate objects
to exist.

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 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.

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.

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.

Authors: R. Kostik, E. Khomenko and N. Shchukina
A&A 506, 1405 (2009) Received 7 May 2009 / Accepted 10 August 2009
Keywords: MHD; Sun: magnetic fields; Sun: oscillations, MHD; Sun: magnetic fields; Sun: oscillations

Authors: C. Pittori, F. Verrecchia, A. W. Chen, A. Bulgarelli, A. Pellizzoni, A. Giuliani, S. Vercellone, F. Longo, M. Tavani, P. Giommi, G. Barbiellini, M. Trifoglio, F. Gianotti, A. Argan, A. Antonelli, F. Boffelli, P. Caraveo, P. W. Cattaneo, V. Cocco, S. Colafrancesco, T. Contessi, E. Costa, S. Cutini, F. D'Ammando, E. Del Monte, G. De Paris, G. Di Cocco, G. Di Persio, I. Donnarumma, Y. Evangelista, G. Fanari, M. Feroci, A. Ferrari, M. Fiorini, F. Fornari, F. Fuschino, T. Froysland, M. Frutti, M. Galli, D. Gasparrini, C. Labanti, I. Lapshov, F. Lazzarotto, F. Liello, P. Lipari, E. Mattaini, M. Marisaldi, M. Mastropietro, A. Mauri, F. Mauri, S. Mereghetti, E. Morelli, E. Moretti, A. Morselli, L. Pacciani, F. Perotti, G. Piano, P. Picozza, M. Pilia, C. Pontoni, G. Porrovecchio, B. Preger, M. Prest, R. Primavera, G. Pucella, M. Rapisarda, A. Rappoldi, E. Rossi, A. Rubini, S. Sabatini, P. Santolamazza, E. Scalise, P. Soffitta, S. Stellato, E. Striani, F. Tamburelli, A. Traci, A. Trois, E. Vallazza, V. Vittorini, A. Zambra, D. Zanello and L. Salotti
A&A 506, 1563 (2009) Received 4 February 2009 / Accepted 3 August 2009
Keywords: gamma rays: observations, catalogs

In the nineteenth century, astronomers recognized
that stars could be classified by their spectra into a handful
of types.  Over time, this system was refined to characterize
a star in terms of prototypical stars with similar spectra.
This is the meaning of the jargon that the Sun is a G2 V
star: the G2 refers to the pattern of lines in the Sun's
spectrum, which is directly dependent on temperature, and
the V refers to the widths of these lines, which are
dependent on luminosity.  The advantage of this system
is that astronomers can determine what stars are like the
Sun in temperature and luminosity simply by looking at
the patterns of lines in the stars' spectra.

Author: A. Claret
A&A 506, 1335 (2009) Received 4 May 2009 / Accepted 8 July 2009
Keywords: stars: atmospheres, planetary systems

Authors: A. Chiavassa, B. Plez, E. Josselin and B. Freytag
A&A 506, 1351 (2009) Received 3 February 2009 / Accepted 14 July 2009
Keywords: stars: supergiants, stars: atmospheres, hydrodynamics, radiative transfer, techniques: interferometric

A class of object, long predicted by astrophysicists,
sits in the mass range between the giant gaseous planets
and the M dwarf stars.  These objects are called brown
dwarfs.  They are massive enough to burn deuterium, but they
are too light to burn hydrogen.  The first brown dwarf was
observed orbiting an M dwarf star in 1988, and since that
time, hundreds of additional brown dwarfs have been found.
They are cool, so they are primarily emitters of infrared
radiation.  In the early stages of their lives, they are
powered by deuterium fusion and gravitational potential
energy, but when they consume their deuterium, and when
the electron degeneracy pressure stops their shrinkage,
they grow cold and dark.