GREEN COMET APPROACHES EARTH
NASA
The greenish-looking Comet Lulin, named after the observatory in
Taiwan where the discovery photo was taken, will make its closest
approach to the Earth (0.41 AU) on Feb. 24. Current estimates give
the maximum brightness as 4th or 5th magnitude, which means that dark
skies would be required to see it. No one can say for sure, however,
because this appears to be Lulin's first visit to the inner Solar
System and its first exposure to intense sunlight. Lulin's green
colour comes from the gases that make up its Jupiter-sized atmosphere.
Jets from the comet's nucleus contain cyanogen (CN -- observed in many
comets) and diatomic carbon (C2); both substances glow green when
illuminated by sunlight in the near-vacuum of space. The comet rises
a few hours before the Sun and will be at about 30 degrees altitude in
the southern sky before dawn. It may be easiest to find on Feb. 16,
when it passes near Spica, and on Feb. 24, when it will be just a few
degrees from Saturn in the constellation Leo.
NEW TECHNIQUE TO MEASURE ASTEROIDS
ESO
Interferometry employing multiple telescopes can determine the sizes
and shapes of asteroids that are too small or too far away to be
resolved by other techniques, and may increase by a large factor the
number of asteroids that can be measured. Direct imaging with adaptive
optics on the largest ground-based telescopes such as the Very Large
Telescope (VLT) in Chile, space telescopes, or radar measurements are
the currently used methods of asteroid measurement. However, direct
imaging, even with adaptive optics, is generally limited to the
largest asteroids of the main belt, while radar measurements are
mostly limited to observations of near-Earth asteroids that have close
encounters with our planet.
In recent experiments with the VLT interferometer, the light from two
of the 8.2-metre 'unit telescopes' was combined, affording a resolving
power equivalent to that of a telescope having an aperture equal to
the separation between the two telescopes used, in this case 47
metres. In principle the interferometer ought to be able to resolve
asteroids as small as about 15 km in diameter in the main asteroid
belt, 200 million kilometres away. In the only actual result so far
reported, the researchers observed the main-belt asteroid (234)
Barbara, which was earlier found to have rather unusual properties.
The observations indicated that that object has indeed a peculiar
shape. The best model (still only tentative) suggests that the
asteroid consists of two bodies with diameters of 37 and 21 km,
separated by at least 24 km.
HYDROCARBON RAINS MAY FILL TITAN LAKES
Cassini Imaging Laboratory
Saturn's largest satellite, Titan, is the only satellite in the Solar
System with a thick atmosphere in which complex chemistry occurs. For
several years, Cassini scientists have suspected that dark areas near
Titan's poles might be liquid-filled lakes. Recent pictures of the
south-polar region show new lake features that were not seen in images
taken a year ago of the same area. The fact that extensive cloud
systems covered the area in the intervening year suggests that the new
lakes could be the result of a heavy rain of hydrocarbons, and that
lakes may owe their presence, size and distribution across Titan's
surface to the moon's weather and changing seasons. Cassini has now
surveyed nearly all of Titan's surface at high resolution. The
observations suggest that there is more liquid methane in the northern
hemisphere than in the southern. Cassini scientists think that, as
the northern hemisphere moves toward summer, large convective cloud
systems will form there, and precipitation greater than that inferred
in the south could extend the northern lakes.
Some of the north-polar lakes are large. If full, Kraken Mare, at
400,000 square kilometres, would be almost five times the size of
North America's Lake Superior. The north-polar dark 'lake' areas
observed by Cassini total more than 510,000 square kilometres --
almost 40% larger than the Earth's largest lake, the Caspian Sea.
However, it does not seem likely that evaporation from the lakes could
be enough to replenish the methane lost from the atmosphere by
rainfall and by the formation and eventual deposition on the surface
of methane-derived haze particles. Combined with previous analyses,
the observations suggest that underground methane reservoirs must
exist.
MANY BROWN DWARFS IN STAR-FORMING REGION
Subaru Telescope facility
Approximately 6,000 light-years away in the constellation Cassiopeia,
there is a very active and massive star-forming region called W3 Main.
Recently a team of Japanese and Indian astronomers has been using the
Subaru telescope in Hawaii to look for dim low-mass stars, and has
found a considerable number of brown dwarfs in the W3 Main region.
That result is significantly different from the one obtained in the
cases of the Trapezium and IC 348, where the relative number of brown
dwarfs is fewer.
TELESCOPE SEES SMALLEST EXOPLANET
BBC News
The smallest exo-planet yet found has been detected by the French
space telescope Corot. The object is less than twice the size of the
Earth and is one of only a few planets so far found with masses
comparable with that of the Earth. About 330 exo-planets have been
discovered so far, but most of them are gas giants similar to Jupiter
or Neptune. The new find, Corot-Exo-7b, orbits a Sun-like star once
every 20 hours and has a temperature between 1,000 and 1,500C.
The vast majority of exo-planets has been discovered by the radial-
velocity method, which was initially developed by the person who edits
these Bulletins. That method favours the detection of large planets
orbiting close to their parent stars. The new planet was detected
photometrically by the transit method, as it crossed the face of the
star, blocking a small fraction of the star's light as it passed in
front. The transit method, too, favours the detection of big planets,
because they block out more light from the parent star, but in a case
-- such as this one -- of a small star then a moderate-sized planet
can be enough to block out enough light for the dimming to be
detected.
GAMMA-RAY FLARE STAR
NASA
The Swift and Fermi spacecraft are monitoring a neutron star, 30,000
light-years from the Earth, that is drawing attention to itself with a
series of powerful gamma-ray flares. At times, that remarkable object
has erupted with more than a hundred flares in as little as 20
minutes; the most intense flares emitted more total energy than the
Sun does in 20 years. The star, known as SGR J1550-5418, lies in the
southern constellation Norma. It began a series of modest eruptions
on 2008 Oct. 3, settled down for a while, then had an intense episode
on 2009 Jan 29. Because of its rapid outbursts and gamma-ray
spectrum, astronomers classify the object as a 'soft-gamma-ray
repeater' -- only the sixth known. In 2004, a giant flare from
another soft-gamma-ray repeater was so intense that it ionized the
Earth's upper atmosphere from 50,000 light-years away!
Using data from an X-ray telescope on Swift, astronomers saw the first
'light echoes' to have been observed from a soft-gamma-ray repeater.
Images acquired when the latest flaring episode began show what appear
to be expanding haloes around the source. Multiple rings form as
X-rays interact with dust clouds at different distances. Scientists
think the source of the flares is a spinning 'magnetar', a neutron
star with an incredibly intense magnetic field. One theory of soft-
gamma-ray repeaters holds that the flares are caused by 'starquakes'
in the outer rigid crust of the magnetar. As a magnetar's colossal
magnetic field shifts, it strains the crust with enormous magnetic
forces, often breaking it. When the crust snaps, it vibrates with
seismic waves as in an earthquake and emits a flash of gamma-rays.
STARS FORMING AT MAXIMUM SPEED
Science Daily
Galaxies, such as our own Milky Way, contain billions of stars.
Theoreticians would like to know how such gigantic systems came into
being -- did the central region form first and then grow, or did the
stars form at the same time throughout the entire galaxy? An
international team led by the Max Planck Institute for Astronomy is
now a bit closer to the answer to those questions. The researchers
studied one of the most distant known galaxies, a quasar with the
designation J1148+5251. Light from it has taken 12.8 billion years to
reach the Earth, so the observations show the galaxy as it was all
that time ago, providing a glimpse of the very early stages of
galactic evolution, less than a billion years after the Big Bang.
With the IRAM interferometer, a German/French/Spanish radio telescope,
the observers recorded the infrared radiation emitted by J1148+5251 at
a specific frequency associated with ionized carbon atoms, which is a
reliable indicator of ongoing star formation. The resulting images
show sufficient detail to allow, for the first time, the measurement
of the size of a very early star-forming region. The researchers
concluded that, at that time, stars were forming in the core region of
J1148+5251 at record rates. Every year, that galaxy's central region
produced new stars with a combined mass of more than a thousand Suns.
By contrast, the rate of star formation within our own galaxy, the
Milky Way, is roughly one solar mass per year.
It has been known for some time that young galaxies can produce
impressive amounts of new stars, but overall activity is only part of
the picture. Without knowing the star-forming region's size, it is
impossible to compare star formation in early galaxies with
theoretical models, or with star-forming regions in our own galaxy.
With a diameter of only 4000 light-years (for comparison, the Milky
Way galaxy's overall diameter is something like 100,000 light-years),
the star-forming core of J1148+5251 is extremely productive. In fact,
it is close to the limit imposed by physical laws. Stars are formed
when cosmic clouds of gas and dust collapse under their own gravity.
As they collapse, temperatures rise, and internal pressure starts to
build up. Once that pressure has reached certain levels, all further
collapse is brought to a halt, and no additional stars can form. The
result is an upper limit on how many stars can form in a given volume
of space in a given period of time. Remarkably, the star-forming core
of J1148+5251 appears to be operating at that absolute limit.
Topic: Mid February Astronomy News (Read 979 times)