MERCURY MISSION CLEARS HURDLE
BBC News
The European Space Agency (ESA) has approved greatly increased expense
for a mission to Mercury. BepiColombo, due for launch in 2014, was
supposed to cost ESA £595m, but the challenge of building a probe able
to survive the torrid heat and radiation it would suffer has pushed
the price up to £950m. It will be baked directly by the Sun,
receiving some 14,000 watts per square metre, about 10 times what a
spacecraft in orbit around the Earth receives. Developing systems that
that can cope with such an environment has led to the mission getting
heavier. Overall, the launch mass has grown from some three tons to
just over four tons, necessitating a larger, more expensive rocket --
an Ariane-5 instead of a Soyuz.
BepiColombo is a joint endeavour with the Japanese. Two probes will
travel to Mercury, and separate when they achieve orbit (in 2020).
Europe will produce a Mercury Planetary Orbiter which will be equipped
with 11 scientific instruments. Flying in a polar orbit, it will
study Mercury for at least a year, imaging the planet's surface,
generating height profiles, and collecting data on Mercury's
composition and wispy atmosphere. Japan will be responsible for the
Mercury Magnetospheric Orbiter. It will investigate the planet's
magnetic field with its five on- board instruments.
JUPITER SATELLITE NAMED
IAU
The IAU has announced that the 50th confirmed satellite of Jupiter,
S/2003 J 17, is to be named Herse.
V445 PUPPIS MAY BE A TYPE-1a SUPERNOVA PROGENITOR
ESO
The double-star system V445 Puppis is a candidate to become one of the
exploding stars known as Type Ia supernovae. V445 Puppis is the
first, and so far only, nova showing no evidence at all for hydrogen.
It provides the first evidence for an outburst on the surface of a
white dwarf dominated by helium. That is suggestive, as we know that
Type Ia supernovae lack hydrogen and the companion star in V445 Pup
also lacks hydrogen, instead dumping mainly helium onto the white
dwarf. In November 2000, the system underwent a nova outburst,
becoming 250 times brighter than before and ejecting a large quantity
of matter into space.
A supernova is one way that a star can end its life. One sort is
called Type Ia. A defining characteristic of Type Ia supernovae is
lack of hydrogen -- yet hydrogen is the most abundant element in the
Universe. Such supernovae most probably arise in systems composed of
two stars, one of which is a white dwarf. The white dwarf in such a
system can accumulate on its surface matter lost by its companion, but
usually only to a small extent before a surface explosion, that we see
as a nova outburst, occurs and ejects much, perhaps all, of the
accumulated matter back into space.
Astronomers have used an adaptive-optics instrument on the VLT to
obtain images of V445 Puppis over a time span of two years. The
images show a bipolar shell, initially with a very narrow waist, with
lobes on each side. The shell -- unlike any previously observed for a
nova -- is expanding at about 7000 km/s. A thick disc of dust, which
must have been produced during the outburst, obscures the two central
stars. Combining the images with data obtained with other telescopes,
the astronomers determined the distance of the system, about 25,000
light-years, and its intrinsic brightness, over 10,000 times brighter
than the Sun. That implies that the white dwarf has a high mass that
is near its fatal limit and is still being fed by its companion at a
high rate. Whether V445 Puppis will eventually explode as a
supernova, or whether the recent nova outburst has pre-empted that
pathway by ejecting too much matter back into space, is unknown.
SPITZER TELESCOPE OBSERVES YOUNG BROWN DWARFS
JPL
The Spitzer infrared space telescope has contributed to the discovery
of the youngest brown dwarfs ever observed. Brown dwarfs are are less
massive and cooler than stars, but more massive (and normally warmer)
than planets. They are often called 'failed' stars, because they lack
the mass necessary to compress their cores to the point where they are
hot enough to ignite the nuclear fusion that burns hydrogen into
helium and powers most stars. They end up as cooler, less-luminous
objects that are difficult to detect. Moreover, young brown dwarfs
evolve rapidly, making it difficult to catch them when they are first
born. In fact, none has been seen in the earliest stages of formation
until now. Now, Spitzer's infrared camera has penetrated a dusty dark
cloud called Barnard 213, a region of the Taurus--Auriga interstellar-
cloud complex well known to astronomers as a hunting ground for young
objects, to observe not one but two of what seem likely to be the
faintest and coolest brown dwarfs ever observed. Observations with
other telescopes have helped to show that the two objects are still
inside the dusty envelope within which they formed.
DARK GALAXY COLLIDING WITH THE MILKY WAY
New Scientist
The Milky Way's neighbourhood may encompass many invisible galaxies,
one of which appears to be colliding with our own. In 2008, a cloud of
hydrogen with a mass then estimated at about 1 million Suns was found
to be colliding with our galaxy. Now it appears that the object is
massive enough to be a galaxy itself. Called Smith's Cloud, it has
managed to avoid disintegrating during its collision with our own,
much bigger galaxy. Furthermore, its trajectory suggests that it
passed through the disc of our galaxy once before, about 70 million
years ago. To have survived, it must contain much more matter than
previously thought, in order to provide enough gravity to hold itself
together. Calculations indicate that it has about 100 times the
previously estimated mass. Simulations of galaxy formation suggest
that a galaxy the size of the Milky Way should be accompanied by about
1000 dwarf galaxies, but only a few dozen have been found so far.
Some of the dwarfs which are (according to the simulation) missing may
be dark galaxies that are all-but invisible.
VESTIGE OF MILKY WAY'S BUILDING BLOCKS?
ESO
The galactic bulge is a troublesome region of our galaxy for
astronomical observations: only infrared light can penetrate its dust
clouds and reveal its myriads of stars. Observations made with the
VLT have shown an unusual mix of stars in a stellar grouping within
the bulge, known as Terzan 5. It appears that that object, unlike all
but a few exceptional globular clusters, does not consist of stars
that were all born at the same time, but formed in at least two
different episodes, about 12 billion and 6 billion years ago. Only
one globular cluster with a similar complex history of star formation
has been observed in the halo of the Milky Way, and that is Omega
Centauri. The new observations show that Terzan 5 is more massive
than previously thought: along with the complex composition and
troubled star-formation history of the system, that suggests that it
might be the surviving remnant of a disrupted proto-galaxy, which
merged with the Milky Way during its very early stages and thus
contributed to the formation of the galactic bulge.
UNIVERSE MAY BE PEPPERED WITH BLUE DWARF GALAXIES
Topix
Astronomers have discovered that the Universe is peppered with tiny
blue dwarf galaxies known as 'blue fuzzies'. The 'tiny' galaxies are
made up mostly of young hot stars that shine brightly, dominating the
light from the galaxies concerned. The discovery was made by
astronomers at the Anglo-Australian Observatory while examining data
from the 'Galaxy and Mass Assembly' survey (GAMA). The aim of the
survey is to map the structure in our local Universe much better than
previous surveys. It incorporates data from the Sloan Digital Sky
Survey, which contains more than 930,000 galaxies and 120,000 quasars,
and extends to approximately 2.5 billion light-years away. When the
astronomers obtained more detailed observations of one of the blue
fuzzies imaged by the survey, they was surprised to discover that it
was in fact an entire galaxy. Since that first discovery, the team
has examined about a hundred more blue fuzzies. The discovery
suggests that the 'nearby' Universe is not dominated by big galaxies
such as the Milky Way or Andromeda, but by lots of small ones.
The blue fuzzies are about the same size as the Small Magellanic
Cloud, averaging around 7000 light-years across and containing as much
mass as seven billion Suns. They are old galaxies, but unlike Milky-
Way-sized galaxies that form stars very rapidly, the blue fuzzies have
their stars forming at a slow but steady pace, giving them a frosting
of young hot stars. They are scattered fairly evenly throughout the
Universe at distances ranging out to seven hundred million light
years. While their distribution follows the voids and filaments which
make up the structure of the cosmos, they seem to be more common in
less-dense areas, away from the large galaxies and galaxy clusters.
Topic: Early December Astronomy Bulletin (Read 728 times)