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 Post subject: ENB No. 223 June 24 2007
PostPosted: Sun Jun 24, 2007 2:47 pm 
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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 223 2007 June 24
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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 visiting http://popastro.c.topica.com/maagQ4Iabzrx7cixLLVb/


SMALLEST GALACTIC OBJECT WITH JET
ESO

Jets of matter have been discovered around a brown dwarf, mimicking a
process seen in young stars. The brown dwarf has a mass of only 24
Jupiter-masses, and it has a 5-Jupiter-mass 'gas-giant' planet which
was the first confirmed exoplanet for which astronomers obtained an
image. Later it was found that the brown dwarf has a disc surrounding
it, not unlike very young stars. Now outflowing jets have been
discovered, making the brown dwarf by far the smallest object known to
drive an outflow. The outflows were discovered by a technique known
as spectro-astrometry, based on high-resolution spectra taken with the
VLT. While in normal young stars -- known as T-Tauri stars for the
prototype of their class -- the jets are large and bright enough to be
seen directly, in this case the length-scale of the jets is only about
0.1 arcsecond. The jets are about 1 billion kilometres long and the
speed of the outflow is a few kilometres per second.


GAMMA-RAY BURST DISCOVERY
Science Daily

U.S. astronomers have concluded that flares seen after a gamma-ray
burst are a continuation of the burst itself. Gamma-ray bursts
release in seconds the amount of energy that the Sun will emit during
its whole expected 10-billion-year lifetime. The energy is thought to
come from the core of a massive star collapsing to form a black hole
or neutron star.

Early in its mission, the Swift satellite's X-ray telescope discovered
that the initial pulse of gamma-rays -- known as prompt emission -- is
often followed by short-lived but powerful X-ray flares, suggesting
that a GRB's central engine remains active long after the prompt
emission. The pattern points to a continuous injection of energy from
the central engine, perhaps fuelled by sporadic infall of material
onto a black hole.


HOT ARC OF GAS IN GALAXY CLUSTER
Harvard-Smithsonian Center for Astrophysics

Astronomers have found a bright arc of very hot gas extending more
than 2 million light-years in a cluster of galaxies filled with
tenuous gas at 170 million degrees Celsius. They say that the
creation of such an arc would have required one of the most energetic
events ever detected. The favoured explanation, though not free of
difficulties, is that two massive clusters of galaxies are colliding
at about 2000 km/s.


PLANET'S YEAR LASTS JUST 31 HOURS
Lowell Observatory

Astronomers using a network of small automated telescopes in Arizona,
California and the Canary Islands, constituting the 'Trans-atlantic
Exoplanet Survey' and looking for transiting planets, has announced
the discovery of its third planet, which is in the constellation
Hercules and orbits its parent star in just 31 hours.


DISTANT QUASAR FOUND
Canada-France-Hawaii Telescope

A team of astronomers using the 8-m Gemini-South Telescope in Chile
has obtained the spectrum of a quasar with a red-shift of 6.43,
slightly higher than any previously recorded shift. It is in the
constellation Pisces and was initially identified as a candidate for a
high-redshift quasar in a survey being made with the Canada-France-
Hawaii telescope in Hawaii.


MOST MASSIVE STARS DISCOVERED
New Scientist

The two most massive stars ever recognized are orbiting one another
every 3.8 days in the star cluster NGC 3603, 20,000 light-years away
near the centre of the Milky Way. The primary is 114 times as massive
as the Sun, the secondary 84 times. There are already a few stars
known that are thought to exceed 100 solar masses, but this is the
first time that one has actually been measured to exceed that mass.
The two previous record-holders also form a binary-star system, called
WR20a, and are around 80 solar masses each. Estimates of the absolute
upper mass limit vary, but the primary of the object in NGC 3603 must
be close to self-destruction. One reason why such stars are extremely
rare in the Galaxy is that they are expected to race through their
stock of hydrogen fuel and explode, all within a few million years.


GRBs ACCELERATE MATTER TO NEARLY THE SPEED OF LIGHT
ESO

Gamma-ray bursts (GRBs) are powerful explosions occurring in distant
galaxies. They are discovered by dedicated satellites, and emit such
power in gamma rays as briefly to outshine by far their whole
galaxies. They last, however, for only a very short time, from less
than a second to a few minutes. It has been thought that, in order to
emit such incredible power, the exploding material must be moving at a
speed close to that of light, 300 000 km/s. By studying the temporal
evolution of the burst luminosity, it has now been possible to
estimate the actual velocity. The observations were made by a robotic
telescope called REM at the ESO La Silla Observatory in Chile.

The collision as the material of the burst jets into the surrounding
gas generates an afterglow that may be visible in the optical and
near-infrared for several weeks. Twice in 2006 the 'Swift' satellite
detected bright gamma-ray bursts. In a matter of seconds, each
position was transmitted to the ground, and the REM telescope began
automatically to observe the field, to detect the near-infrared
afterglow, and to monitor the variation of the luminosity as a
function of time (the light-curve). The telescope is small but slews
quickly; it began observations very soon -- only 39 and 41 seconds
after the GRB alerts, respectively -- and was able to monitor the
very early stages of their light-curves.

According to Stefano Covino, co-author of the study, matter is moving
with a speed that differs from that of light by only three parts in a
million. While single particles can be accelerated to still larger
velocities -- i.e. much larger Lorentz factors -- in the present
cases, it is the equivalent of about 200 times the mass of the Earth
that has acquired that incredible speed. The next question is what
kind of 'engine' can accelerate matter to such enormous speeds.


TWO MORE ACTIVE MOONS AROUND SATURN
Nature

Saturn's moons Tethys and Dione are ejecting streams of particles into
space, according to data from the Cassini mission. The particles were
traced to the two moons through the motion of electrically charged gas
in the magnetic environs of Saturn. Known as plasma, the gas is
composed of negatively charged electrons and positively charged ions,
which are atoms with one or more electrons missing. Because they are
charged, the electrons and ions can get trapped inside a magnetic
field. Saturn's rotation, which takes 10 hours and 46 minutes, sweeps
the magnetic field and the trapped plasma round with it. Previously,
among Saturn's inner moons only Enceladus was known to be active, with
geysers spraying gases hundreds of kilometres above the surface. The
new result seems to be a strong indication that there is activity on
Tethys and Dione as well.


30 VARIABLE STARS FOUND IN M23 CLUSTER
Luther College

Astronomers have used a 12-inch telescope over a span of 39 months to
acquire more than 155,000 images of M23, an open star cluster in
Sagittarius, as part of a long-term study of fields containing bright
open star clusters. The study hopes to shed light on how a wide
variety of stars vary over many years by monitoring the luminosity
stability of normal stars, searching for changes in the periods and
amplitudes of variable stars, and waiting for any flares or outbursts.
Variability was found in 30 stars and possible variability in many
more. Only two of the stars were previously known to be variable.
Among the variables are seven eclipsing binaries, three of them with
orbital periods shorter than 14 hours; in two of them the surfaces of
the stars are in contact. If the contact binaries prove to be members
of the star cluster rather than foreground or background stars, that
will fix their ages because the cluster age can be determined.
Observation of contact binaries in many clusters of varying ages might
help astronomers to estimate the minimum time it takes for contact
systems to form from more widely separated pairs.


ANCIENT MARS OCEAN SHORELINE
Astronomy

Some scientists are claiming that long, undulating features on the
northern plains of Mars are remnants of shorelines of an ocean that
covered a third of the planet's surface at least 2 billion years ago.
The features, stretching thousands of miles, were first seen in the
1980s in Viking spacecraft images, but in the 1990s the Mars Global
Surveyor found major variations in elevation along the suspected
shorelines, whereas a shoreline should be at a constant elevation.
Scientists writing in the journal Nature now say, however, that the
movement of the Martian poles and the planet's spin axis by roughly
2,000 miles in the past 2 to 3 billion years could have caused
deformation of surface features just like that seen in the suspected
coastlines.


MASS OF FORMER 'TENTH PLANET'
New Scientist

Eris -- formerly but informally known as Xena -- is the Pluto-sized
body, discovered in the trans-Neptunian Kuiper Belt in 2005, that
re-ignited a debate over the definition of a planet and became a
'dwarf planet' -- a new category of object that included Pluto
-- when astronomers officially defined the term in 2006. It has a
tiny satellite, Dysnomia, about 1/16 of its own size. Now, Caltech
researchers using the Keck telescope in Hawaii and the Hubble space
telescope have found that Dysnomia is in a 15-day circular orbit, and
from that they have been able immediately to determine that Eris has a
mass 27% larger than that of Pluto. Since Eris is slightly larger
than Pluto, having a diameter of 2400 km against Pluto's 2320 km, its
larger mass is not surprising. Its density, too, is quite similar to
Pluto's and suggests that Eris is made of rock and ice.




Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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