I appear to have forgotten to post this at the appropriate time!
TAIL DISCOVERED ON ASTEROID HYGIEA
Carnegie Institution
A new active asteroid, numbered 62412, has been discovered in the main
asteroid belt between Mars and Jupiter. It is the first comet-like
object seen in the Hygiea family of asteroids. Active asteroids are a
newly recognized phenomenon and 62412 is only the 13th known active
asteroid in the main asteroid belt. It is estimated that there may
be about 100 of them in the main asteroid belt. Active asteroids
have stable orbits between Mars and Jupiter like other asteroids;
unlike other asteroids, however, they sometimes have the appearance of
comets, when dust or gas is ejected from their surfaces, creating a
sporadic tail effect. Astronomers recently discovered a tail on
62412, an object which had been known as an ordinary asteroid for over
a decade. The reasons for the loss of material and the formation of a
tail in active asteroids are unknown, although there are several
theories such as recent impacts or sublimation from solid to gas of
exposed ices.
In the past, asteroids were thought to be mostly unchanging objects,
but an improved ability to observe them has allowed scientists to
discover tails and comas, the latter being like the thin envelopes of
atmosphere surrounding comets' nuclei. Discoveries such as this one
can help researchers to determine the processes that cause some
asteroids to become active. They found that 62412 has a very fast
rotation that may shift surface material, some of which may leave the
surface and form the comet-like appearance. The tail may be created
directly from material ejected from the fast-rotating body, or from
ice within it subliming into water vapour after being freshly exposed
on the surface. The density of 62412 has been found to be typical of
primitive asteroids and not consistent with the much lower densities
comets.
JUPITER'S GREAT RED SPOT MAY BE CAUSED BY SUNLIGHT
NASA
The ruddy colour of Jupiter's Great Red Spot is probably caused by
simple chemicals being broken apart by Sunlight in the planet's upper
atmosphere, according to a new analysis of data from the Cassini
mission. Astronomers arrived at their conclusions from a combination
of data from Cassini's 2000 December Jupiter fly-by and laboratory
experiments. In the lab, the researchers irradiated ammonia and
acetylene gases -- chemicals known to exist on Jupiter -- with
ultraviolet light, to simulate the Sun's effects on those materials at
the extreme heights of clouds in the Great Red Spot. That produced a
reddish material, which the team compared to the Great Red Spot as
observed by Cassini. They found that the light-scattering properties
of their red concoction matched a model of the Great Red Spot in which
the red-coloured material is confined to the uppermost reaches of the
feature. Their models suggest that most of the Spot is actually
pretty bland in colour, beneath the upper cloud layer of reddish
material. Under the reddish 'sunburn' the clouds are probably whitish
or greyish. A colouring agent confined to the top of the clouds would
be inconsistent with the competing theory, which posits that the
Spot's red colour is due to upwelling chemicals formed deep beneath
the visible cloud layers. If red material were being transported from
below, it should be present at other altitudes as well, which would
make the Great Red Spot redder still.
Jupiter is composed almost entirely of hydrogen and helium, with just
a sprinkling of other elements. Scientists wish that they could
understand what combinations of elements are responsible for the
hues seen in Jupiter's clouds, as that would provide insights into the
planet's make-up. The team initially set out to determine if the
Great Red Spot's colour might derive from Sun-induced breakdown of a
more complex molecule, ammonium hydrosulphide, which makes up one of
Jupiter's main cloud layers. They quickly found that, instead of a
red colour, the products their experiment produced were a brilliant
green! That surprising negative result prompted them to try simple
combinations of ammonia with hydrocarbons that are common at Jupiter's
high altitudes. Breaking down ammonia and acetylene with ultraviolet
light turned out to give the best fit to the data collected by Cassini.
The Great Red Spot is a long-lived feature in Jupiter's atmosphere and
is twice the size of the Earth. Jupiter possesses three main cloud
layers, which occupy specific altitudes in its skies; from highest to
lowest they are: ammonia, ammonium hydrosulphide and water clouds.
As to why the intense red colour is seen only in the Great Red Spot
and a few much smaller spots on the planet, the researchers think that
altitude plays a key role. The Great Red Spot is extremely tall and
reaches much higher altitudes than clouds elsewhere on Jupiter. The
team thinks that the Spot's great height both enables and enhances the
reddening. Its winds transport ammonia-ice particles higher into the
atmosphere than usual, where they are exposed to much more of the
Sun's ultraviolet light. In addition, the vortex nature of the Spot
confines particles, preventing them from escaping. That causes the
redness of the Spot's cloud tops to increase beyond what might
otherwise be expected.
EXTREME STORMS ON URANUS
University of California - Berkeley
The normally bland face of Uranus has become increasingly stormy, with
enormous cloud systems so bright that, for the first time ever,
amateur astronomers are able to see details in the planet's hazy
blue-green atmosphere. Such activity might have been expected in
2007, when Uranus's once-every-42-years equinox occurred and the Sun
shone directly on the equator, but astronomers thought that any such
activity would have died down by now. In all, astronomers detected
eight large storms on Uranus's northern hemisphere when they observed
the planet at the Keck Observatory on August 5 and 6. One was the
brightest storm ever seen on Uranus at 2.2 microns, a wavelength that
senses clouds just below the tropopause (the lower boundary of the
stratosphere), where the pressure ranges from about 300 to 500 mbar,
or half the pressure at the Earth's surface. The storm accounted for
30% of all the light reflected by the planet at that wavelength. When
amateur astronomers heard about the activity, they turned their
telescopes on the planet and were able to see a bright blotch on the
surface of the normally bland blue dot. Interestingly, the extremely
bright storm seen by the 10-m Keck II telescope in the near infrared
is not the one seen by the amateurs, which is much deeper in the
atmosphere than the one that initially caused all the excitement.
Scientists have identified the amateurs' spot as one of the few
features on the Keck images from August 5 that was seen only at 1.6
microns, and not at 2.2 microns. The 1.6-micron light is emitted from
deeper in the atmosphere, which means that the feature concerned is
below the uppermost cloud layer of methane ice in Uranus's atmosphere.
The colours and morphology of the cloud complex suggest that the storm
may be tied to a vortex in the deeper atmosphere, similar to two large
cloud complexes seen during the equinox. Such vortices could be
anchored much deeper in the atmosphere and extend over large vertical
distances.
Uranus is an ice giant, about four times the diameter of the Earth,
with an atmosphere of hydrogen and helium, with just a bit of methane
that gives it a blue tint. Because it is so distant -- 19 times
farther than the Earth is from the Sun -- astronomers were never able
to see much detail on its surface until adaptive optics on the Keck
telescopes revealed features much like those on Jupiter. Keck
observers have been following Uranus for more than a decade, charting
the weather on the planet, including bands of circulating clouds,
massive swirling storms and convective features at its north pole.
Because Uranus has no internal source of heat, its atmospheric
activity is thought to be driven solely by sunlight, which is now weak
in the northern hemisphere, so astronomers were surprised to see such
intense activity.
EXO-ZODIACAL LIGHT DETECTED
ESO
Astronomers using the Very Large Telescope Interferometer have
discovered 'zodiacal light' close to the 'habitable zones' around nine
nearby stars. That light is starlight reflected from dust created as
the result of collisions between asteroids and the evaporation of
comets. The interferometer was used in near-infrared light to observe
92 nearby stars to look for exo-zodiacal light from hot dust close to
their 'habitable zones'.
From dark clear sites on Earth, our Zodiacal Light looks like a white
glow in the part of the night sky along the ecliptic after the end of
twilight, or before dawn. It is brightest nearest the Sun but in good
conditions can be followed right around the ecliptic. There is an
enhancement called the Gegenschein at the anti-solar point. It is
created by Sunlight reflected off tiny particles and appears to extend
out from the vicinity of the Sun. The reflected light is seen not
just from the Earth but can be observed from everywhere in the Solar
System. The glow being observed in the new study is a much more
extreme version of the same phenomenon. While such 'zodiacal light'
had been detected previously around other stars, this is the first
large systematic study of the phenomenon around nearby stars.
In contrast to earlier observations, the team did not observe dust
that will later form into planets, but dust probably created in
collisions between planetesimals -- objects a few kilometres in size
that are probably similar to the asteroids and comets of the Solar
System. Dust of that kind is also the origin of the Zodiacal Light in
the Solar System. By analysing the properties of the stars surrounded
by dust discs, the team found that most of the dust was detected
around older stars. That result was very surprising and raises some
questions for our understanding of planetary systems. Any known dust
production caused by collisions of planetesimals should diminish over
time, as the number of planetesimals is reduced as they are destroyed.
The sample of observed objects included 14 stars for which the
detection of exo-planets has been reported. All of those planets are
in the same regions of the systems as the dust that gives the
exo-zodiacal light. Exo-zodiacal dust emission, even at low levels,
makes it significantly harder to detect Earth-like planets by direct
imaging. The exo-zodiacal light detected in the Keck survey is a
thousand times brighter than the Zodiacal Light seen around the Sun.
The number of stars with zodiacal light at the level of the Solar
System is most likely much higher than the numbers found in the
survey. The observations made so far are therefore only a first step
in studies of exo-zodiacal light.
PLANET-FORMING LIFELINE IN BINARY STAR SYSTEM
ESO
Researchers using the Atacama Large Millimetre/submillimetre Array
(ALMA) have detected a streamer of gas flowing from a massive outer
disc toward the inner reaches of a binary star system. That feature
may be responsible for sustaining a second, smaller disc of planet-
forming material that otherwise would have disappeared long ago. It
has been proposed that half of all Sun-like stars are born in binary
systems, so that finding may be significant for the hunt for
exo-planets. The research group observed the distribution of dust and
gas in a multiple-star system called GG Tau A. That object is only a
few million years old and lies about 450 light-years away in the
constellation Taurus. Like a wheel within a wheel, GG Tau A contains
a large, outer disc encircling the entire system as well as an inner
disc around the central star. The inner disc has a mass roughly
equivalent to that of Jupiter. Its presence has puzzled astronomers,
since it appears to be losing material to its central star at a rate
that ought to have depleted it long ago.
While observing those structures with ALMA, the team made the
discovery of gas clumps in the region between the two discs. The new
observations suggest that material is being transferred from the outer
to the inner disc, creating a sustaining lifeline between the two.
The material from the outer disc can sustain the inner one for a long
time. That has a significant bearing on potential planet formation.
Planets are born from the material left over from star birth. That is
a slow process, so an enduring disc is a prerequisite for planet
formation. If the feeding process into the inner disc now seen with
ALMA occurs in other multiple-star systems, then there are many new
potential locations to find exo-planets in the future. The first
phase of exo-planet searches was directed at single stars like the
Sun. More recently it has been shown that many giant planets orbit
binary-star systems. Now, researchers have begun to investigate the
possibility of planets orbiting the individual stars of multiple-star
systems. The new discovery supports the possible existence of such
planets, giving exo-planet discoverers new hunting grounds.
BINARY STARS MERGE AT GALACTIC CENTRE
University of California - Los Angeles
For years, astronomers have found interest in an object in the centre
of the Milky Way that was believed to be a hydrogen-gas cloud headed
towards our Galaxy's enormous black hole. Having studied it with the
Keck telescope in Hawaii during its closest approach to the black hole
this summer, astronomers believe that they now understand the object
widely known as G2. The team has determined that G2 is most likely a
pair of binary stars that had been orbiting the black hole in tandem
and merged together into an extremely large star, cloaked in gas and
dust -- its movements choreographed by the black hole's powerful
gravitational field. Astronomers had supposed that if G2 were a
hydrogen cloud, it should have been torn apart by the black hole, but
actually G2 survived and continued on its orbit; a simple gas cloud
would not have done that. G2 was basically unaffected by the black
hole. Black holes, which form out of the collapse of matter, cannot
be seen directly, but their influence on nearby stars is visible and
provides a signature. G2 appears to be just one of an emerging class
of stars near the black hole that are created because the black hole's
powerful gravity drives binary stars to merge into one. In our
Galaxy, massive stars often come in pairs.
When two stars near the black hole merge into one, the merged object
is enlarged for more than a million years before it settles back down.
That may be happening more than has previously been thought. The
stars at the centre of the Galaxy are massive and mostly binaries. It
seems possible that many of the stars that we have been watching and
not understanding may be the end product of mergers that are now calm.
The team also determined that G2 appears to be in the inflated stage
now. The body has fascinated many astronomers in recent years,
particularly during the year leading up to its approach to the black
hole. G2 is undergoing what is called 'spaghettification' -- a common
phenomenon near black holes, in which large objects become elongated.
At the same time, the gas at G2's surface is being heated by stars
around it, creating a cloud of gas and dust that has shrouded most of
the massive star.
WHEN DID GALAXIES SETTLE DOWN?
RAS
Astronomers have long wished that they understood how the Universe
evolved from its earliest history to the state in which we see it now.
In particular, the way that galaxies form and develop is still a
matter for debate. Now a group of researchers has used the collective
efforts of the hundreds of thousands of people who volunteer for the
'Galaxy Zoo' project to shed some light on that problem. They find
that galaxies may have settled into their current form some two
billion years earlier than was previously thought. The team set Zoo
volunteers the task of classifying the shapes of tens of thousands of
galaxies observed by the Hubble telescope. The objects are typically
very distant, so we see them as they appeared more than 10 billion
years ago, when the Universe was about 3 billion years old, less than
a quarter of its present age. The newly classified galaxies are
striking in that they look a lot like those in today's Universe, with
discs, bars and spiral arms. But theorists reckon that those should
have taken another 2 billion years to begin to form, so things seem to
have settled down a lot earlier than expected. Galaxy simulations
suggested that there shouldn't be any of the barred features that we
see in nearby, evolved galaxies, because very young galaxies would be
too agitated for them to form. But we now know that is not the case.
SOUNDING ROCKET RE-DEFINES GALACTIC BOUNDARIES
NASA
A sounding-rocket experiment has detected a surprising surplus of
infrared light in the dark space between galaxies, a diffuse cosmic
glow as bright as all known galaxies combined. The glow is thought to
be from orphaned stars flung out of galaxies. The findings could
re-define what scientists think of as galaxies. Galaxies may not have
a set boundary of stars, but instead stretch out to great distances,
forming an inter-connected sea of stars. Observations from the Cosmic
Infrared Background ExpeRiment, or CIBER, are helping to settle a
debate on whether that background infrared light, previously detected
by the Spitzer space telescope, comes from streams of stripped stars
too distant to be seen individually, or alternatively from the first
galaxies to form. It is likely that stars are being scattered out
into space by collisions between galaxies. While astronomers have
previously observed cases where stars are flung from galaxies in a
tidal stream, the new measurement implies that that process is
widespread. Using sub-orbital sounding rockets, which are smaller
than those that carry satellites into orbit and are ideal for short
experiments, CIBER captured wide-field pictures of the cosmic infrared
background at two infrared wavelengths shorter than those observed by
Spitzer. Because our atmosphere itself glows brightly at those
wavelengths, the measurements can be done only from space.
During the CIBER flights, the cameras launch into space, then take
pictures for about seven minutes before transmitting the data back to
Earth. Scientists masked out bright stars and galaxies from the
pictures and carefully ruled out any light coming from more local
sources, such as our own Milky Way Galaxy. What was left is a map
showing fluctuations in the remaining infrared background light, with
splotches that are much bigger than individual galaxies. The
brightness of the fluctuations allows scientists to measure the total
amount of background light. To the surprise of the CIBER team, the
maps revealed a substantial excess of light beyond what comes from the
galaxies. The data showed that the infrared background light has a
spectrum that increases in brightness towards shorter wavelengths --
evidence that it comes from a previously undetected population of
stars between the galaxies. Light from the first galaxies would give
a spectrum that is redder than what was seen. The light seems too
bright and not red enough to be coming from the first generation of
galaxies, and the simplest explanation is that many stars have been
ejected from their galaxies and together emit about as much light as
the galaxies themselves. Future experiments can test whether stray
stars are indeed the source of the infrared cosmic glow. If the stars
were ejected from their parent galaxies, they should still be located
in the same vicinities. The CIBER team is working on better measure-
ments using more infrared colours to learn how the stripping of stars
happened over cosmic history.
POLAND TO JOIN ESO
ESO
The Polish Minister of Science and Higher Education has signed an
agreement that will lead to her country joining the European Southern
Observatory (ESO) following ratification of the accession agreement.
The connection between ESO and Poland extends beyond their respective
astronomical communities. For example, the most recent ESO Industry
Day was hosted in Warsaw last year. That event gave ESO the chance to
inform Polish industry about the current project, the European
Extremely Large Telescope (E-ELT). Poland has a rich tradition in
astronomy, from the time of Copernicus to the present day.
Topic: Late November Astronomy Bulletin (Read 1439 times)