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.

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.

Authors: D. Adén, S. Feltzing, A. Koch, M. I. Wilkinson, E. K. Grebel, I. Lundström, G. F. Gilmore, D. B. Zucker, V. Belokurov, N. W. Evans and D. Faria
A&A 506, 1147 (2009) Received 18 June 2009 / Accepted 13 August 2009
Keywords: galaxies: dwarf, galaxies: fundamental parameters, galaxies: individual: Hercules, galaxies: kinematics and dynamics, galaxies: photometry

Authors: G. Bihain, R. Rebolo, M. R. Zapatero Osorio, V. J. S. Béjar, I. Villó-Pérez, A. Díaz-Sánchez, A. Pérez-Garrido, J. A. Caballero, C. A. L. Bailer-Jones, D. Barrado y Navascués, J. Eislöffel, T. Forveille, B. Goldman, T. Henning, E. L. Martín and R. Mundt
A&A 506, 1169 (2009) Received 26 March 2009 / Accepted 31 July 2009
Keywords: stars: luminosity function, mass function, Galaxy: open clusters and associations: individual: \sigma Orionis, stars: low-mass, brown dwarfs

Authors: G. Consolini, R. Tozzi and P. De Michelis
A&A 506, 1381 (2009) Received 2 October 2008 / Accepted 5 June 2009
Keywords: Sun: activity, Sun: sunspots, methods: statistical, chaos

Authors: M. A. T. Groenewegen, G. C. Sloan, I. Soszy?ski and E. A. Petersen
A&A 506, 1277 (2009) Received 11 June 2009 / Accepted 20 August 2009
Keywords: stars: AGB and post-AGB, stars: mass loss, Magellanic Clouds

Author: M.-R. L. Cioni
A&A 506, 1137 (2009) Received 24 March 2009 / Accepted 9 August 2009

Keywords: galaxies: abundances, Magellanic Clouds, Local Group, stars: AGB and post-AGB, galaxies: stellar content, galaxies: individual: M33

Authors: D. Ruždjak, H. Boži?, P. Harmanec, R. Fi?t, P. Chadima, K. Bjorkman, D. R. Gies, A. B. Kaye, P. Koubský, D. McDavid, N. Richardson, D. Sudar, M. Šlechta, M. Wolf and S. Yang
A&A 506, 1319 (2009) Received 4 July 2008 / Accepted 24 August 2009
Keywords: stars: early-type, binaries: spectroscopic, stars: emission-line, Be, stars: individual: \zeta Tauri