PLUTO HAS CARBON MONOXIDE IN ATMOSPHERE
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British astronomers have discovered carbon monoxide in the atmosphere
of Pluto. Pluto was discovered in 1930 and then considered as the
smallest and most distant planet. Since 2006 it has been officially
regarded as a 'dwarf planet', one of four such bodies with sizes of
hundreds of kilometres that orbit beyond Neptune. Pluto is the only
dwarf planet known to have an atmosphere, detected in 1988 when it
dimmed the light of a distant star before Pluto passed in front of it.
The new results, obtained in Hawaii with the 15-m James Clerk Maxwell
telescope which operates at sub-mm wavelengths, show a strong signal
of carbon monoxide. Previously the atmosphere was known to be over
100 km deep, but the new data raise its depth to more than 3000 km --
a quarter of the way out to Pluto's largest moon, Charon. The gas is
extremely cold, about -220°C. A surprise for the team was that
the signal is more than twice as strong as an upper limit obtained
with the IRAM 30-m telescope in Spain in 2000. The suggestion is that
the atmosphere may have grown in size, or the carbon monoxide
abundance may have increased. Such changes have been seen before but
only in the lower atmosphere, where methane -- the only other gas ever
positively identified there -- has been seen to vary.
Pluto was at perihelion in 1989, a comparatively recent event given
that it takes 248 years to complete each orbit. The gases probably
result from solar heating of surface ice, which evaporates as a
consequence of the slightly higher temperatures during the perihelion
passage. The resulting atmosphere is probably the most fragile in the
Solar System, with the top layers blowing away into space. Unlike the
greenhouse gas carbon dioxide, carbon monoxide acts as a coolant,
while methane absorbs sunlight and so produces heating. The balance
between the two gases, which are just trace elements in what is
thought to be a nitrogen-dominated atmosphere, is critical for its
fate during the many-decades-long seasons. The newly discovered
carbon monoxide may hold the key to slowing the loss of the atmosphere
-- but if the chilling effect is too great, it could result in
nitrogen snowfalls and all the gases freezing out onto the ground.
DID A SUPERNOVA MARK THE BIRTH OF A MONARCH?
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The supernova remnant Cassiopeia A (Cas A) is the relic of an
explosion that took place around 11,000 years ago of a massive star,
and is one of the brightest radio sources in the sky. Oddly, although
the light from the explosion should have reached the Earth in the
seventeenth century and been easily visible in the sky, it seems to
have gone unnoticed. Now astronomer Martin Lunn and historian Lila
Rakoczy argue that the supernova was seen as a 'New Star' visible
during the daytime at the birth of the future King Charles II of Great
Britain.
The generally accepted period that the explosion of Cas A should have
been seen is the latter half of the seventeenth century. Mr. Lunn,
former Curator of Astronomy at the Yorkshire Museum, and Dr. Rakoczy,
a US-based independent scholar, suggest instead that Cas A could have
been seen earlier, on 1630 May 29. That date is better known to
historians as the day that King Charles II of Great Britain was born,
and is also significant for a 'Noon-day star' alleged to have appeared
at his birth, an important feature of later Stuart/Restoration
propaganda. Separate sources refer to the star over an interval of
about 30 years. The star has been widely discussed by historians and
literary scholars, but its credibility as a genuine astronomical event
has remained largely unexplored. Lunn and Rakoczy believe that it
deserves further investigation. Lunn comments, "The number and
variety of sources that refer to the new star strongly suggest that an
astronomical event really did take place. Our work raises questions
about the current method for dating supernovae, but leads to the
exciting possibility of solving a decades-old astronomical puzzle."
FIRST GALAXIES BORN MUCH EARLIER
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Using the amplifying power of a cosmic gravitational lens, astronomers
claim to have discovered a distant galaxy that began forming stars
just 200 million years after the Big Bang. That challenges theories
of how soon galaxies formed and evolved. The distant galaxy is
visible through a cluster of galaxies called Abell 383, whose powerful
gravity bends the rays of light almost like a magnifying glass. The
chance alignment of the galaxy, the cluster and the Earth amplifies
the light reaching us from this distant galaxy, allowing the
astronomers to make detailed observations. Without the gravitational
lens, the galaxy would be too faint to be observed even with the
largest telescopes. After finding the galaxy in Hubble and Spitzer
images, the team carried out spectroscopic observations to measure
its redshift and infer some properties of its component stars.
The galaxy's redshift is 6.027, which means that we see it as it was
when the Universe was around 950 million years old. It is not the
most remote galaxy ever detected, but it seems quite different from
other distant galaxies, which generally show the signature of young
stars. The Spitzer infrared detection indicated that the new galaxy
was made up of stars already nearly 750 million years old -- pushing
back the epoch of its formation to about 200 million years after the
Big Bang, much further than expected. The work confirms some earlier
observations that had hinted at the presence of old stars in early
galaxies. The discovery has implications beyond the question of when
galaxies first formed, and may help explain how the Universe became
transparent to ultraviolet light in the first billion years after the
Big Bang. In the early years of the cosmos, a diffuse fog of neutral
hydrogen gas blocked ultraviolet light in the Universe. Some source of
radiation must have progressively ionized the diffuse gas, clearing
the fog to make it transparent to ultraviolet rays as it is today -- a
process known as re-ionization. Astronomers believe that the
radiation that powered the re-ionization must have come from galaxies,
but so far nowhere near enough of them have been found to provide the
necessary radiation. A sufficiently rash extrapolation from the one
new discovery might suggest that there are far more galaxies out there
in the early Universe than were previously estimated, but that they are
older and fainter.
FORMATION OF COMPACT GALAXIES
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Astronomers at Bristol University have found some evidence that
explains how unusual galaxies called compact ellipticals (cEs) are
formed, and have discovered two examples in which they see the process
of formation in action. Compact elliptical galaxies are small in size
and high in brightness. There are two main theories as to how they
are formed. One involves the stripping of a more massive galaxy,
leaving a smaller remnant galaxy behind. The other argues that cE
galaxies are the smallest members of the standard class of elliptical
galaxies. Until now, the evidence supporting the stripping idea has
been circumstantial. The astronomers discovered in the Sloan Digital
Sky Survey (SDSS) two cEs in which the process of stripping is taking
place, and another one in archival data from the 4-m CFHT. The images
showed streams of stars being torn from the cE galaxies and leaving
small bright remnants behind. Although the observed cEs show that
stripping is certainly one way in which these galaxies form, it does
not exclude other mechanisms; analysis of the many other cE candidates
found in the Bristol study may show any alternatives that may exist.
LARGE GALAXIES STOPPED GROWING 7 BILLION YEARS AGO
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How galaxies form and then evolve is still a major question. They
have been thought to develop by the gravity-induced coalescence of
smaller 'sub-galaxies', a process that standard cosmological ideas
suggest should be ongoing. But new data from scientists from
Liverpool John Moores University challenge that idea, suggesting that
the growth of some of the most massive objects stopped 7 billion years
ago when the Universe was half its present age. The sub-galaxy units
thought to have merged to make galaxies are themselves associated with
fluctuations in the density of material in the cosmos after the 'Big
Bang' and seen today as temperature 'ripples' in the cosmic background
radiation.
To study galaxy evolution, the team looked at the most massive
galaxies in the Universe, known as Brightest Cluster Galaxies (BCGs)
and so called because of their locations at the centres of galaxy
clusters, structures that typically contain hundreds of galaxies.
In the 'nearby' Universe BCGs are elliptical in shape and are the
largest, most uniform and most massive class of galaxies observed,
with each galaxy having a mass equivalent to up to 10*(14) Suns. Like
smaller elliptical galaxies, BCGs are composed of old red stars and
are thought to have formed through mergers of the dense populations of
sub-galaxies that were found in the centres of galaxy clusters.
Measuring the sizes of BCGs has always been difficult, as their outer
regions are very faint. The team found in the Hubble telescope
archive some long-exposure images that pick up the outer parts of the
galaxies. The light that they studied left the BCGs 7 billion years
ago, so the galaxies appear as they were when the Universe was less
than half its present age; but the distant BCGs are almost the same
size as their nearby counterparts, and it seems that the latter can
have grown by at most 30% in the last 7 billion years. Some previous
attempts to simulate the evolution of the Universe suggested that BCGs
should have at least tripled in size over that time.
WAIT ANOTHER FEW YEARS
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Astronomers have produced a new catalogue of about 15,000 groups of
galaxies that may give a new insight into dark matter, the material of
unknown composition that is said by some to make up a fifth of the
mass of the Universe. Current models of the Universe put galaxies in
large clumps of dark matter, commonly referred to as dark matter
haloes. Galaxy groups provide an opportunity to try to discover the
properties of the elusive material, by a study of the motions of the
galaxies inside the groups; studying dark matter in individual
galaxies is confused by normal processes such as star formation,
whereas the unseen material dominates the motions of galaxies in
groups. Although the catalogue has now been compiled, it will take a
further few years of study, with a large range of models, before any
definite conclusions can be reached.
LOW-COST SPACE MISSIONS
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Constrained budgets mean that some good proposals for space missions
do not come to fruition. There is an enormous spread in the costs of
access to space. NASA, ESA etc have a range of mission opportunities
that deliver several years of data, but with price tags of £100M and
more, and those opportunities occur typically at a rate of only one
every 2-3 years. Sub-orbital programmes through sounding rockets are
more frequent and allow data to be obtained for a few million pounds.
However, they offer only a few minutes' observing time above the
atmosphere, restricting the scientific goals that can be achieved.
Balloon programmes offer longer-duration flights, up to a few days,
but are suitable only for gamma-ray, visible-light or infra-red
studies. X-ray, extreme-UV and UV-wavelength radiation does not
penetrate far enough into the atmosphere to be detectable by
instruments on balloons.
Prof. Martin Barstow has recently promoted his idea that there is
a need for the development of an intermediate class of mission
that provides access to low Earth orbit (altitudes between 160 and
2000 km) at a cost of £10-20m, allowing a greater number of missions
than at present. One method he proposes to deliver such lower-cost
space missions is to re-cycle proven sub-orbital instruments,
eliminating a significant proportion of the usual development
expenses, and up-rating support systems such as attitude control and
power to operate for several months rather than a few minutes. He
claims that the UK has considerable expertise in low-cost satellite
technologies. Seemingly ignoring the risk that he will be seen to be
grinding his own axe, he gives, as an example of an instrument that
could be flown at low cost, an extreme-ultraviolet spectrograph,
which he says is very good, developed by his own group.
Topic: Late April Astronomy Bulletin (Read 807 times)