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.

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.

Most type Ia supernovae are attributed to the
thermonuclear explosion of white dwarfs.  A star becomes a
white dwarf before it has completely consumed its thermonuclear
fuel.  The amount of thermonuclear energy locked within a white
dwarf is of order 0.1% of the white dwarf's rest mass energy.
Theorists have three theories that explain what triggers the
release of this energy, with each theory relying on the
white dwarf being a member of a binary system.  The preferred
theory is that the white dwarf grows in mass by pulling gas from
its companion onto itself until it becomes gravitationally
unstable; when the white dwarf collapses, its internal pressure
and temperature rise until thermonuclear reactions cause it
to explode.

Recently some people have claimed that the Sun
is entering a new Maunder Minimum—a decades-long period
of few sunspots—and that this will cause the Earth's
atmosphere to cool.  The Sun is certainly quiet in 2008,
but this is the normal quiet of a minimum in the 11 year
sunspot cycle.  Clearly the tendency to interpret normal
variations as fundamental changes is not confined to the
global warming alarmists.

Carbon and oxygen are converted into nickel
in a white dwarf through a complex network of reactions.
The incremental changes tend to follow the series of atomic
nuclei that are multiples in composition of the helium
nucleus.  For this reason, large amounts of neon-20,
magnesium-24, silicon-28, and other elements with equal
and even numbers of protons and neutrons are created.  But
the reactions also tear down nuclei, creating many free
protons, neutrons, and helium nuclei that combine with
other atomic nuclei to produce elements and isotopes
that do not have equal numbers of protons and neutrons
or do not have an even number of protons or of
neutrons.  Because thermonuclear fusion disrupts
a white dwarf, the thermonuclear reactions in
a white dwarf  contribute to the rich variety
of chemical elements and isotopes we find throughout
the universe.

The structure of a brown dwarf is set by
degeneracy pressure.  Unlike a star, where the mass
sets both the radius and the photospheric temperature,
a brown dwarf has a radius and temperature that is nearly
independent of its mass.  All brown dwarfs are about
the same size as Jupiter.  The photospheric temperature
of a brown dwarf is set by its age, although the lifetime
of a brown dwarf is set by the mass.  Because the
low-mass brown dwarfs cool much faster than the
high-mass brown dwarfs, infrared surveys preferentially
find the more-massive brown dwarfs.

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.

Authors: H. S. P. Müller, B. J. Drouin and J. C. Pearson
A&A 506, 1487 (2009) Received 20 July 2009 / Accepted 15 August 2009
Keywords: molecular data, methods: laboratory, techniques: spectroscopic, radio lines: ISM, ISM: molecules

Authors: J.-F. Lestrade, M. C. Wyatt, F. Bertoldi, K. M. Menten and G. Labaigt
A&A 506, 1455 (2009) Received 8 April 2009 / Accepted 6 July 2009
Keywords: stars: circumstellar matter, stars: low-mass, brown dwarfs, planetary systems: formation

Authors: N. Crimier, C. Ceccarelli, B. Lefloch and A. Faure
A&A 506, 1229 (2009) Received 12 January 2009 / Accepted 5 August 2009
Keywords: ISM: abundances, ISM: molecules, stars: formation

Authors: S. Linden, J.-M. Virey and A. Tilquin
A&A 506, 1095 (2009) Received 2 July 2009 / Accepted 11 August 2009
Keywords: cosmology: cosmological parameters, cosmology: observations, stars: supernovae: general, surveys

Authors: L. Shrbený and P. Spurný
A&A 506, 1445 (2009) Received 8 April 2009 / Accepted 29 June 2009
Keywords: techniques: photometric, meteors, meteoroids

Authors: B. Ascaso, J. A. L. Aguerri, M. Moles, R. Sánchez-Janssen and D. Bettoni
A&A 506, 1071 (2009) Received 29 December 2008 / Accepted 2 July 2009
Keywords: galaxies: clusters: general, galaxies: structure, cosmology: observations