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Tuesday, 15 March 2011

SPA ENB No. 306

                 The SOCIETY for POPULAR ASTRONOMY
         Electronic News Bulletin No. 306      2011 March 6
 Here is the latest round-up of news from the Society for Popular
Astronomy.  The SPA is Britain's liveliest astronomical society, with
members all over the world.  We accept subscription payments online
at our secure site and can take credit and debit cards. You can join
or renew via a secure server or just see how much we have to offer by
University of Hawaii
A telescope called Pan-STARRS on Haleakala, an extinct volcano on Maui
(one of the Hawaiian islands), discovered 19 near-Earth asteroids on
the night of January 29, the most such asteroids discovered by one
telescope on a single night.  Asteroids are easy to discover, on an
image that goes sufficiently deep, because they appear to move
against the background of stars, and nearby ones move quickly.  To
confirm such discoveries and to determine the orbits so that the
objects can be found again and recognised in the future, several
observations need to be made within a few days.  Details of
discoveries are sent to the Minor Planet Center in Cambridge,
Massachusetts, which collects and disseminates data about asteroids
and comets so that other astronomers can re-observe the objects.
Widespread snowstorms had closed down many observatories in North
America, but telescopes in Italy, Japan and the UK, and the Faulkes
Telescope on Haleakala, as well some in mainland America, helped to
confirm seven of the January 29 discoveries.  The original observers
themselves spent the next three nights searching for the asteroids
with telescopes at Mauna Kea in Hawaii.  On the 30th they confirmed
that two of them were near-Earth asteroids before snow on Mauna Kea
obliged the telescopes to close.  On the 31st, they confirmed nine
more before fog set in.  (The impression is given that observing
conditions are not uniformly perfect even at the best places!)  Two
days later they searched again for four, but found only one. After
that, the remaining unconfirmed ones would had moved too far to be
found again.  [Impossible to say how many were confirmed and how many
not -- the numbers don't add up unless indeed the 19 referred to at
the beginning is to be taken as the number of *confirmed* discoveries.
- ED.]
BBC News
The spacecraft 'Messenger' is due to enter orbit around Mercury on
17 March, if everything goes according to plan.  It has already made
three fly-bys of the planet in the course of adjusting its orbit so as
to reduce the velocity change needed for orbit insertion.  The only
previous spacecraft to visit Mercury was Mariner 10, which made
several passes in the 1970s but did not go into orbit around the
planet.  It sent back pictures that looked very much like those of the
Moon.  Mercury seemed to some people at the time to be uninteresting
in comparison with Venus, Mars and the outer planets.  But
observations from the Earth began to show that it is far from being
boring.  It is a planet of extremes: although it is the closest to the
Sun, yet it could have ice at its poles, and it has a metal core that
is larger than any other in relation to the size of the planet.
Obviously we can hope to learn far more from an orbiting craft than
from one that just flies past.
Using the Very Large Telescope, astronomers have been able to study
the short-lived disc of material around a young star that is in the
early stages of making a planetary system.  For the first time a
smaller companion could be detected that may be the cause of a large
gap found in the disc.  Future observations will determine whether the
companion is a planet or a brown dwarf.  Planets form from the discs
of material around young stars, but the transition from dust disc to
planetary system is rapid and few objects are caught during that
phase.  One such object is T Chamaeleontis (T Cha), a faint star that
is comparable to the Sun but very near the beginning of its existence.
T Cha lies about 100 parsecs away and is only about seven million
years old.  Up to now no forming planets have been found in such
transitional discs, although planets in more mature discs have been
seen before.
The astronomers found that some of the disc material formed a narrow
dusty ring only about 20 million kilometres from the star.  Outside
that inner disc, they found a region devoid of dust out to 1.1 billion
kilometres from the star, beyond which radius there was further dusty
material.  They considered that they could see the signature of an
object located within the gap in the dust disc, about one billion
kilometres from the star -- slightly further out than Jupiter is
within our Solar System and close to the outer edge of the gap.  That
is the first detection of an object much smaller than a star within a
gap in the supposedly planet-forming dust disc around a young star.
The evidence suggests that the companion object cannot be a normal
star but it could be either a brown dwarf surrounded by dust or else a
recently formed planet.
The discovery of a rapid decline in the temperature of an ultra-dense
star has provided the first evidence for a bizarre state of matter in
the core of a star.  Astronomers have used data from the Chandra X-ray
Observatory to show that the interior of a neutron star contains
superfluid and superconducting matter, a conclusion with important
implications for understanding nuclear interactions in matter at the
highest known densities.  That news comes from studies of the
supernova remnant Cassiopeia A (Cas A), the remains of a massive star
that exploded about 330 years ago as seen from here.  A sequence of
Chandra observations of the neutron star, the ultra-dense core that
remained after the supernova, shows that that object has cooled by
about 4% over a ten-year period.
Neutron stars contain the densest matter known.  The pressure in the
star's core is so high that most of the electrons there are forced to
merge with protons, producing neutrons.  That leaves a star composed
mostly of neutrons, with some protons, electrons and other particles.
Theoretical physicists have dreamed up detailed models for how matter
should behave at such high densities, including the possibility that
superfluids may form.  Superfluidity is a friction-free state of
matter, and superfluids created in laboratories on Earth exhibit
remarkable properties, such as the ability to climb upward and escape
from airtight containers.  Superfluids made of charged particles are
also superconductors, which allow electric currents to flow with no
resistance. (Such materials have widespread technological applications
on Earth, for instance in the superconducting magnets in magnetic
resonance imaging (MRI) machines used in hospitals).
The rapid cooling in Cas A's neutron star is the first evidence that
the cores of such stars are made of superfluid and superconducting
material.  Astronomers say that the rapid cooling is explained by the
formation of a neutron superfluid in the core of the star, within
about the last 100 years as seen from the Earth.  Theory suggests that
a neutron star should undergo a distinct cool-down during the
transition to the superfluid state, as nearly massless, weakly
interacting particles, called neutrinos, are copiously formed and then
escape from the star, taking energy with them.  The rapid cooling is
expected to continue for a few decades and then to slow down.  The
onset of superfluidity in materials on Earth occurs at extremely low
temperatures near absolute zero, but in neutron stars it may be able
to occur at temperatures near a billion degrees.  However, until now
there has been a very large uncertainty in estimates of the critical
temperature, which the new research constrains to between half a
billion and just under a billion degrees C.
Scientists have extended a directly-measured 'yardstick' three times
further into the cosmos than ever before, an achievement with
important implications for numerous areas of astrophysics, The
continent-wide Very Long Baseline Array (VLBA) can produce images
hundreds of times more detailed than those from the Hubble telescope.
New measurements with the VLBA have placed the galaxy NGC 6264 at a
distance of 450 million light-years, with an uncertainty of no more
than 9%.  That is the furthest distance ever directly measured.  Until
recently, distances beyond our own Galaxy have been estimated through
indirect methods.
The VLBA is also re-drawing the map of our own Galaxy.  Recent work
has added dozens of new measurements to star-forming regions in the
Milky Way.  The direct VLBA measurements improve on earlier estimates
by as much as a factor of two.  That improvement significantly aids in
understanding the physics of the young stars and their environments.
Earlier work showed that the Milky Way is rotating faster than
previous estimates had indicated.  That measurement in turn showed our
Galaxy to be more massive, equalling our neighbour, the Andromeda
Galaxy, in mass.
Bulletin compiled by Clive Down
(c) 2011 the Society for Popular Astronomy
Good Clear Skies
Colin James Watling
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)

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