ORPHANED PLANET DISCOVERED
ESO
Astronomers have identified an object that is probably a planet
wandering through space without a parent star. At a distance of about
100 light-years, it is the closest such object so far discovered.
Its comparative proximity, and the absence of a bright star very close
to it, has allowed the team to study its atmosphere. The object also
gives astronomers a preview of the exo-planets that they hope future
instruments will image around stars other than the Sun. Free-
floating planets are planetary-mass objects that roam through space
without any ties to a star. Possible examples of such objects have
been found before, but without knowledge of their ages, it was not
possible for astronomers to know whether they were really planets or
brown dwarfs ('failed stars') that lack the mass to trigger the
nuclear reactions that make stars shine. The new object, labelled
CFBDSIR2149, may be associated with the 'AB Doradus moving group',
which is the closest such group to the Solar System. If so, then it
is a young object, and it is possible to deduce much more about it,
including its temperature, mass, and what its atmosphere is made of.
There remains a possibility that the association with the moving group
is by chance. Free-floating objects like CFBDSIR2149 are thought to
form either as normal planets that have been ejected from the
vicinities of their parent stars, or as lone objects like the smallest
stars or brown dwarfs.
GAS AND DUST AROUND 49 CETI
ScienceDaily
Over the past three decades, astronomers have discovered hundreds of
dusty discs around stars, but only two -- 49 Ceti is one -- also have
large amounts of gas orbiting them. Young stars, about a million
years old, have discs of both dust and gas orbiting them, but the gas
almost always dissipates within about 10 million years. Yet 49 Ceti,
which is thought to be about 40 million years old, is still being
orbited by a large quantity of gas in the form of carbon monoxide
molecules. Astronomers do not know why there should be so much gas
around an otherwise ordinary star that is that old. The gas may be in
a massive disc region, perhaps rather similar to the Sun's Kuiper Belt,
although 49 Ceti is a much brighter star than the Sun -- it is more
like Sirius.
The total mass of the various objects that make up the Kuiper Belt,
which lies beyond the orbit of Neptune and includes Pluto, is about
one-tenth the mass of the Earth. But when the Sun was young, the
Kuiper Belt may have had a mass as much as 40 times the Earth's. The
possible analogue that orbits around 49 Ceti, however, now has a mass
of about 400 Earth masses. Innumerable comets may orbit around
49 Ceti and also round one other star whose age is about 30 million
years. Young comets probably contain more carbon monoxide than
typical comets in our Solar System. When they collide, the carbon
monoxide escapes as a gas. It is suggested that the gas seen around
the two stars is the result of an incredible number of collisions
among their comets -- but that begs a question, because the comets
must have been formed from carbon monoxide (among other things) in
the first place.
PLANETARY NEBULA EXPLAINED?
ESO
Astronomers using the Very Large Telescope (VLT) have discovered a
pair of stars orbiting each other at the centre of a remarkable
planetary nebula. The new result supports a suggestion about what
controls the spectacular and symmetrical appearance of the nebula.
Planetary nebulae are glowing shells of gas around white dwarfs --
formerly-Sun-like stars in the final stages of their evolution.
'Fleming 1' is a beautiful example that has strikingly symmetrical
jets that weave into knotty, curved patterns. It is in the southern
constellation Centaurus and was discovered just over a century ago by
Williamina Fleming, a former maid who was hired by Harvard College
Observatory after showing an aptitude for astronomy.
Astronomers have wondered how the symmetrical jets could be created,
but no consensus has been reached. Now, an effort has been made to
combine new observations of Fleming 1 with computer modelling to
explain how the bizarre shapes came about. The team used the VLT to
study the light coming from the central star and found that Fleming 1
is likely to have two white dwarfs at its centre, circling each other
every 1.2 days. Although binary stars have been found at the hearts
of planetary nebulae before, systems with two white dwarfs orbiting
one another are rare. Astronomers have suggested a binary star
before, but it was thought that in that case the pair would be well
separated, with an orbital period of tens of years or longer. The new
observations found the pair to be very much closer. When a star
with a mass up to eight times that of the Sun approaches the end of
its evolution, it begins to lose mass by blowing off its outer shells.
That exposes the hot inner core of the star, which radiates strongly,
causing the outward-moving cocoons of gas to glow brightly as a
planetary nebula. Many such nebulae are strikingly complex, with
knots, filaments, and intense jets of material forming intricate
patterns. The new study indicates that the patterns for Fleming 1 are
the result of the close interaction between the pair of stars -- the
surprising swan song of a stellar couple. This is the most
comprehensive case yet of a binary central star for which simulations
have correctly reproduced the shape of the surrounding nebula.
STAR FORMATION SLUMPS BY 97%
RAS
The current model for the evolution of the Universe supposes that
stars began to form about 13.4 billion years ago, or around three
hundred million years after the Big Bang. Many of the first stars are
thought to have been monsters by today's standards, and were probably
hundreds of times more massive than the Sun. Such objects would have
aged very quickly, exhausted their fuel, and exploded as supernovae
within a million years or so. Lower-mass stars, in contrast, have
much longer lives and last for billions of years. Much of the dust
and gas from stellar explosions was (and still is) recycled to form
fresh generations of stars. Our Sun, for example, is thought to be a
third-generation star, and has a very typical mass by today's
standards. But regardless of their mass and properties, stars are key
ingredients of galaxies like our own Milky Way. Unveiling the history
of star formation across cosmic time is fundamental to understanding
how galaxies form and evolve.
In a new study, scientists used the UK Infrared Telescope (UKIRT), the
VLT and the Subaru telescope to carry out a survey of star-forming
galaxies at different distances, with around ten times the data of any
previous effort. With the range of distances, the time taken for the
light to reach us means that we see identically selected galaxies at
different periods in the history of the Universe, so we may be able to
understand how conditions changed over time. By looking at the light
from clouds of gas and dust in galaxies where stars are forming, the
team is able to assess the rate at which stars are being born. It
seems that the production of stars in the Universe as a whole has been
continuously declining over the last 11 billion years, being 30 times
lower today than at its peak 11 billion years ago. If the decline
continues, then no more than 5% more stars will form over the
remaining history of the cosmos, even if it lasts for ever. The
research suggests that we live in a Universe dominated by old stars.
Half of them were born in the boom that took place between 11 and 9
billion years ago, and it took five times as long to produce the rest.
CANDIDATE FOR MOST DISTANT GALAXY
Space Telescope Science Institute (STScI)
A new record has been claimed by 'CLASH' (Cluster Lensing And
Supernova Survey with Hubble) for finding the most distant galaxy,
which appears as a diminutive blob that is only a tiny fraction of the
size of our Milky Way galaxy. The CLASH survey is a multi-wavelength
census of 25 massive clusters of galaxies. The programme uses the
'gravitational lensing' effects of such clusters to identify amplified
images of objects behind them. The very distant galaxy, called
MACS0647-JD, is seen as it appeared when its light left it 420 million
years after the 'big bang' when the Universe was only 3% of its
present age of 13.7 billion years. Its light has travelled 13.3
billion years to reach us. Along the way, 8 billion years into its
journey, it found multiple paths around the massive galaxy cluster
MACS J0647+7015. In the absence of the cluster, astronomers would not
have seen it, but because of gravitational lensing, the CLASH research
team was able to observe three magnified images of MACS0647-JD with
the Hubble telescope. The cluster's gravity boosted the light from
the far galaxy, making the images appear about eight, seven, and two
times brighter than they otherwise would be. MACS0647-JD is less than
600 light-years across; for comparison, the Large Magellanic Cloud (a
dwarf-galaxy companion to the Milky Way) is 14,000 light-years across.
MACS0647-JD has a redshift of 11, the highest yet observed.
TYCHO BRAHE 'NOT POISONED'
BBC Online
The 16th-Century Danish astronomer Tycho Brahe is unlikely to have
been poisoned, according to a researcher studying his remains. His
body was exhumed in 2010 in a bid to establish the cause of his death.
Tycho was born Tyge Ottesen Brahe in 1546 in Scania, which at the time
was a Danish province, and studied astronomy at the University of
Copenhagen, as well as at German academic institutions. He catalogued
more than 1,000 new stars, and his stellar and planetary observations
helped lay the foundations of modern astronomy. Brahe's fame is also
partly due to his personal life. He lost the bridge of his nose in a
duel while at the University of Rostock in 1566, and wore a metal
prosthetic for the rest of his life. Tests now indicate that the
prosthetic was in fact made of brass, not gold and silver as accounts
had suggested.
On his death in 1601, he was buried at Tyn Church near Prague's Old
Town Square. His body has been exhumed previously, in 1901. It has
been thought that he died of a bladder infection, but traces of
mercury were found in hair taken from his beard in 1901. However, the
recent tests have found that the level of mercury was not high enough
to have killed him. There has been speculation that he was killed on
the orders of the Danish king, or even by fellow astronomer Johannes
Kepler. A team of Danish and Czech scientists has been working to
solve the problem by analysing bone, hair and clothing samples. The
description given by Kepler of Brahe's death at the age of 54 matches
well the progression of a severe bladder infection. One widely told
story is that his bladder burst at a royal banquet when he had not
dared to leave the table to relieve himself. Accounts say that he
died 11 days later.
GEMINID METEOR SHOWER
By Tony Markham, SPA Meteor Section Director
The 2012 Geminids are very well placed for observation, with their
December peak being almost coincident with New Moon. Although the
Perseids of August attract more observers, the Geminids of December
produce higher rates. Observing the Geminids does, however, pose the
challenges of enduring the cold December nights and a (usually) lower
chance of clear skies than for the Perseids.
The Geminid meteor shower is active from around Dec 7 to Dec 16. This
year's peak is due during the night of Dec 13-14 (Thurs-Fri), most
likely within a few hours of 2330UT. Rates will also be high during
Dec 12-13, but will have dropped off by Dec 14-15. The peak Geminid
ZHR is usually in excess of 100, although actual observed hourly rates
will, of course, depend on the radiant altitude and the darkness of
your observing site. The Geminids are observable throughout the
night. Good numbers of Geminids can be seen from around 8pm onwards,
with the best observed rates likely to be seen between midnight and
2am.
In some ways the Geminids are like the Perseids, being rich in bright
meteors. In other ways they are different, with very few Geminids
leaving persistent trains -- a consequence of the Geminids being more
robust particles derived from asteroid 3200 Phaethon whereas the
Perseids are more fragile icy material derived from comet Swift-
Tuttle.
Topic: Late November Astronomy Bulletin (Read 1257 times)