GLYCINE DISCOVERED IN COMET
Goddard Space Flight Center
NASA scientists have discovered traces of the amino acid glycine in
samples of Comet Wild 2 returned by the Stardust spacecraft. Stardust
passed through dense gas and dust surrounding the icy nucleus of
Wild 2 on 2004 January 2. As the spacecraft shot past, a special
collection grid filled with aerogel -- a novel sponge-like material
that is more than 99% empty space -- 'gently' captured samples of the
comet's gas and dust. The grid was stowed in a capsule that detached
itself from the spacecraft and parachuted to Earth on 2006 January 15.
Since then, scientists have been analyzing the samples to learn a bit
about comet formation and our Solar System's history.
Preliminary analysis detected glycine in the aluminium foil from the
sides of tiny chambers that held the aerogel in the collection grid
and also in a sample of the aerogel. However, since terrestrial life
uses glycine, at first the team was unable to rule out contamination
from sources on Earth. It was possible that the glycine originated
from handling or manufacture of the Stardust spacecraft itself. The
new research used isotopic analysis to adjudicate on that possibility.
A glycine molecule from space will tend to have more carbon-13 atoms
in it than glycine from Earth. The team found that the Stardust
glycine has an extra-terrestrial carbon-isotope signature, indicating
that it originated in the comet.
OLD STAR SHEDS NEW LIGHT ON OLD TIMES
Subaru Telescope Facility
The chemical composition of the old star BD +44 493, recently
investigated with the Subaru telescope, may have relevance to how the
earliest stars developed when the Universe was young. According to
the Big Bang theory, the Universe was initially composed almost
entirely of hydrogen and helium. The creation of heavier elements
occurred later, through the process of nucleosynthesis, in which
more-complex atomic nuclei were formed inside stars. Therefore, the
proportion of heavier elements in an astronomical object (its
'metallicity') may provide an indication of its age. Older stars have
lower metallicities than younger stars such as our Sun. Because their
atmospheres usually preserve the chemical composition of the gas from
which they formed, old, low-metallicity stars retain evidence of the
chemical abundances that existed at the time of their own creation --
information that provides clues to processes occurring early in the
history of the Universe.
That idea has prompted searches for stars with very low metal content;
one called HE1327-2326 has the record for the lowest iron content ever
seen, but its ratio of carbon and nitrogen relative to iron was
remarkably high. Another very iron-deficient star, HE0107-5240, shows
a similar pattern. Astronomers supposed that the metal-enrichment
histories of those two stars were quite different from that of other
low-metal stars. Spectroscopic studies of a larger sample of
metal-deficient stars have been made with the Subaru telescope in an
effort to provide more clues about their early development. At one
point a ninth-magnitude star was observed in twilight as a reference
star for the programme. Analysis showed that that star, BD +44 493,
contained only 1/5000 of the heavy elements of the Sun and was 10
times brighter than any star of such low metallicity known so far.
A follow-up observation showed a relatively high abundance of carbon,
as in the cases mentioned above, and gave abundance ratios for other
elements. The best explanation of the findings is that the star was
formed from a gas cloud polluted by a supernova explosion of a
first-generation massive star, which yielded carbon-rich but
metal-poor material. The measurements of BD +44 493 have thus
provided new evidence of the type of supernovae present in the very
early phase of the Galaxy.
EXTRA-SOLAR PLANET OUGHT NOT TO EXIST
Science Daily
A photometric survey called WASP has discovered a planet that has ten
times the mass of Jupiter but orbits its star in less than a day.
That poses a challenge to the experts' understanding of tidal
interactions in planetary systems. The planet, called WASP-18b,
belongs to a now-common class of extra-solar planets known as 'hot
Jupiters'. It is so massive, and so close to its star -- only about
three stellar radii away -- that tidal interactions between star and
planet ought to cause the planet to spiral inwards to its destruction
in less than a million years. Yet, astronomers think that the WASP-18
parent star is about a billion years old, so either we have to admit
that the likelihood of catching sight of WASP-18b at this critical
time is only about one in a thousand, or else tidal dissipation in the
WASP-18 system somehow manages to be a thousand times less than in our
Solar System. If the planet's remaining existence is as short as
predicted, the orbital decay should be measurable within a decade.
CYGNUS X-1
Science Daily
Since its discovery 45 years ago, Cygnus X-1 has been one of the most
intensively studied cosmic X-ray sources. About a decade after its
discovery, it secured a place in the history of astronomy when a
combination of X-ray and optical observations led to the conclusion
that it was a black hole, the first such identification. The Cygnus
X-1 system is thought to consist of a black hole with a mass about 10
solar masses in a close orbit with a blue supergiant star with a mass
of about 20 Suns. Gas flowing away from the supergiant in a fast
stellar wind is focused by the black hole, and some of it forms a disc
that spirals into the hole. The gravitational energy released by the
infalling gas powers the X-ray emission from Cygnus X-1. Although
more than a thousand scientific articles have been published on Cygnus
X-1, its status as a nearby black hole continues to attract the
interest of scientists seeking to understand the nature of such holes
and how they affect their environment. Observations with Chandra and
XMM-Newton have helped to investigate the properties of the stellar
wind that fuels the emission, and determining the hole's rate of spin.
The conclusion is that Cygnus X-1 is spinning unusually slowly.
STAR-BIRTH RATIO NOT FIXED
CSIRO Australia
Doubt has been cast on a long-held beliefs about how stars are formed.
It has been thought that in a family of new-born stars the ratio of
massive stars to lesser ones was always pretty much the same -- for
instance, that for every star 20 times more massive than the Sun or
larger, there would be 500 stars the mass of the Sun or less. The
distribution of stellar masses at birth is called the 'initial mass
function' (IMF). Most of the light we see from galaxies comes from
stars of the highest mass, while the total mass is dominated by those
of lower masses. By measuring the amount of light from a population
of stars, and making some corrections for the stars' ages, astronomers
can use the IMF to estimate the total mass of that population.
Results for different galaxies can be compared only if the IMF is the
same everywhere, but astronomers have now shown that the ratio of
high-mass to low-mass newborn stars differs between galaxies. For
instance, small 'dwarf' galaxies form many more low-mass stars than
expected. To arrive at that finding, researchers used galaxies from
the HIPASS Survey (H I Parkes All-Sky Survey). Selecting galaxies on
the basis of their neutral hydrogen gave a sample of many different
shapes and sizes, unbiassed by their star-formation histories. The
astronomers measured two tracers of star formation, ultraviolet and
H-alpha emissions, in 103 galaxies with the GALEX satellite and the
1.5-m CTIO optical telescope in Chile. H-alpha emission traces the
presence of very massive stars called O stars, which are born with
masses more than 20 times that of the Sun. The UV emission traces
both O stars and the less-massive B stars -- overall, stars more than
three times the mass of the Sun. The ratio of H-alpha to UV emission
was found to vary from galaxy to galaxy, implying that the IMF did
too, at least at its upper end. That confirms a tentative suggestion
made by French astronomers in 1987. The new research suggests that
the IMF is sensitive to the physical conditions of the star-forming
region.
GIANT GALAXY HOSTS THE MOST DISTANT SUPERMASSIVE BLACK HOLE
RAS
Astronomers have been able to detect the giant galaxy surrounding the
most distant known supermassive black hole. The galaxy, so distant
that it is seen as it was 12.8 billion years ago, is as large as the
Milky Way galaxy and its black hole has a mass at least a billion
times that of our Sun. The galaxy and black hole must have formed
rather 'rapidly' in the early Universe. Knowledge of the host
galaxies of supermassive black holes is needed if astronomers are ever
to understand how galaxies and black holes have evolved together.
After forming, supermassive black holes continue to grow because their
gravity draws in surrounding matter. The energy released in that
process accounts for the light emitted from the regions around the
holes. Studying host galaxies in the distant Universe has been
difficult because the light from the vicinity of the hole swamps that
from the faint galaxy around it. In the case referred to here, the
scientists used CCDs on the Subaru telescope on Mauna Kea. They found
that 40% of the near-infrared light came from the galaxy itself and
60% from the clouds of material surrounding and illuminated by the
black hole.
INDIA LOSES MOON SATELLITE LINKS
BBC
India's space agency has reported that communication with the
Chandrayaan-1 Moon-orbiting spacecraft was lost abruptly just over a
week ago. The craft was launched last October in what was billed as a
two-year mission. Its launch, from the southern state of Andhra
Pradesh, was a major step for India as it seeks to keep pace with
other space-faring nations in Asia. The probe was intended to orbit
the Moon, compiling a 3-D atlas of the surface and mapping the
distribution of elements and minerals. Powered by a single solar
panel generating about 700 watts, the probe carries five instruments
built in India and six constructed in other countries, including the
US, Britain and Germany. The mission was expected to cost £45m,
considerably less than Japanese and Chinese probes sent to the Moon
last year.
Topic: Early September Astronomy Bulletin (Read 1238 times)