PLUTO MAY HAVE NITROGEN GLACIERS
BBC News
New Horizons scientists believe that they see evidence of surface
material having flowed around mountains and even ponding in craters on
Pluto. The activity is certainly recent and may even be current.
But the mission team cautions that it has received only 4-5% of the
data gathered during July 14's fly-by, and any interpretation must be
subject to caveats. New analyses based on the limited data-set that
has already arrived suggest that Pluto has a much more rarefied
atmosphere than was previously supposed. That idea comes from
measurements made by the probe as it was looking back at Pluto after
the fly-by. It could tell from the passage of sunlight and radio
waves through the Plutonian 'air' that the pressure was only about 10
microbars at the surface (1 microbar is about a millionth of the air
pressure on the Earth at sea level). The other key detection was of
hazes in the atmosphere. They may be a consequence of methane at high
altitude being processed by sunlight into less-simple hydrocarbons
like ethylene and acetylene, which then fall, cool and condense to
form a mist of ice particles. Some of that material may be further
processed into more complex chemicals that rain on to the surface and
give certain regions their reddish hue. But it is the idea of glacial
activity having occurred on Pluto that is most likely to capture
public attention. That is interpreted to have happened at the edges
of what has become known as Sputnik Planum -- the great plain in the
western half of Pluto's bright, heart-like feature just north of the
equator.
High-resolution imagery from New Horizons' 'Lorri' camera records wavy
patterns that look just like the flowing ice of glaciers on the Earth
as viewed by satellites. If there is still warmth coming from Pluto's
interior then it could help any surface ices to move down-slope.
Water-ice at Pluto temperatures wouldn't move anywhere; it is immobile
and brittle; but the kind of ices that we think make up the planum
(nitrogen ice, carbon monoxide and methane ices) -- those ices are
quite soft and malleable, even in Pluto conditions, and could flow in
the same way as glaciers do on Earth. So we actually have some
evidence for activity taking place no more than a few tens of millions
of years ago. New Horizons continues to observe Pluto even though it
is now some 12 million km beyond it. The probe is watching as Pluto
makes its slow rotation (6.4 Earth days). The observations will soon
cease, and the spacecraft will be spun up, permitting systems that
help to maintain three-axis stability to be turned off. Their power
usage can then be diverted to the transmitter to boost its output. In
September, engineers will command New Horizons to start sending back
all of the outstanding scientific data that it gathered during the
fly-by. That stored information will be brought down in a compressed
form first of all, followed by an uncompressed return. The whole
process -- encompassing all observations of Pluto and its five moons
-- is not scheduled to be completed until late 2016. However, the New
Horizons team says it will share the discoveries as they are made
during the long down-linking period.
BIGGER, OLDER COUSIN TO EARTH DISCOVERED
NASA
The Kepler mission has found the first near-Earth-size planet in
the 'habitable zone' around a Sun-like star. The newly discovered
Kepler-452b is the smallest planet discovered to date orbiting in the
'habitable zone' -- the region around a star where liquid water could
exist on an orbiting planet -- of a G-type star like our Sun. The
confirmation of Kepler-452b brings the total number of confirmed
planets to 1,030. Kepler-452b is 60% larger in diameter than the
Earth. Although its mass and composition are not yet determined,
previous research suggests that planets the size of Kepler-452b have a
good chance of being rocky. While Kepler-452b is larger than the
Earth, its 385-day orbit very similar to ours. The planet is 5%
further from its parent star than the Earth is from the Sun.
Kepler-452 is 6 billion years old, 1.5 billion years older than the
Sun, has the same temperature, is 20% brighter and has a diameter 10%
larger. To help confirm the finding and determine the properties of
the Kepler-452 system, the team made ground-based observations at the
McDonald, Whipple and Keck observatories.
Those measurements enabled the researchers to confirm the planetary
nature of Kepler-452b, and to refine estimates of the size and
brightness of its host star and the sizes of the planet and its orbit.
The Kepler-452 system is located 1,400 light-years away in the
constellation Cygnus. In addition to confirming Kepler-452b, the
Kepler team has found a lot more exo-planet candidates; however,
candidates require follow-up observations and analysis to verify they
are actual planets. Twelve of the new candidates have diameters
between one to two times that of the Earth, and orbit in their star's
'habitable zone'. Nine of them orbit stars that are similar to the Sun
in size and temperature. Astronomers have been able to automate the
process of identifying planet candidates, so now they can assess every
transit signal in the entire Kepler data set quickly and uniformly,
giving them a statistically sound population of planet candidates from
which they may be able to estimate the number of small, possibly rocky
planets like the Earth in our Galaxy. Scientists are now producing the
last catalogue based on the original Kepler mission's four-year data
set. The final analysis will use new software that has increased
sensitivity to the tiny telltale signatures of Earth-size planets.
JUPITER TWIN DISCOVERED AROUND SOLAR TWIN
ESO
An international group of astronomers has used the 3.6-m telescope at
La Silla in Chile to identify a planet just like Jupiter orbiting at
the Jupiter's distance from a Sun-like star, HD 16008. According to
current theories, the formation of Jupiter-mass planets plays an
important role in shaping the architecture of planetary systems. The
existence of a Jupiter-mass planet in a Jupiter-like orbit around a
Sun-like star opens the possibility that there is a system of planets
around it that may be similar to our own Solar System. HD 16008 is
about the same age as the Sun and its Sun-like composition is claimed
to suggest that there may also be rocky planets orbiting closer to
the star. So far, exo-planet surveys have been most sensitive to
planetary systems that are populated in their inner regions by massive
planets, down to a few times the mass of the Earth. That contrasts
with our Solar System, where there are small rocky planets in the
inner regions and gas giants like Jupiter farther out. According to
the most recent theories, the arrangement of the Solar System,
conducive to life, was made possible by the presence of Jupiter and
the gravitational influence that it exerted on the Solar System during
its formative years. It might seem, therefore, that finding a Jupiter
twin is something of a milestone on the road to finding a planetary
system that mirrors our own.
UNIQUE BINARY SYSTEM DISCOVERED
University of Cambridge
The Gaia satellite has discovered a unique binary system where one
star is 'eating' the other, but neither star has any hydrogen, the
most common element in the Universe. The system could be an important
tool for understanding how binary stars might explode at the ends of
their lives. An international team of researchers, with the
assistance of amateur astronomers, has discovered a binary system of
the type known as cataclysmic variables, where a white-dwarf star is
accreting gas from its companion star. The system, named Gaia14aae,
is located about 730 light-years away in the Draco constellation and
was discovered last August when it suddenly became five times brighter
over the course of a single day. Astronomers analysed the information
from Gaia and determined that the sudden outburst was due to the
exceedingly dense white dwarf cannibalizing its larger companion.
Additional observations of the system, made by the Center for Backyard
Astrophysics, a collaboration of amateur and professional astronomers,
found that the system is an eclipsing binary, where one star passes
directly in front of the other, completely eclipsing it. The two stars
are in a tight orbit, with a total eclipse occurring every 50 minutes.
Using spectroscopy from the William Herschel telescope, the team found
that Gaia14aae contains large amounts of helium, but no hydrogen,
which is highly unusual, as hydrogen is the most common element in the
Universe. The lack of hydrogen allowed them to classify Gaia14aae as
a rare type of system known as an AM CVn star, a type of cataclysmic-
variable system where both stars have lost all of their hydrogen. It
is the first known AM CVn system where one star totally eclipses the
other. AM CVn systems consist of a small and hot white-dwarf star
that is devouring its larger companion. The gravitational effect
from the hot and super-dense white dwarf is so strong that it has
forced the companion star to swell up like a massive balloon and move
towards it. The companion star is about 5 times the diameter of the
Sun, whereas the white dwarf is about the size of the Earth. However,
the companion star has only about 1% of the white dwarf's mass.
DEAD GALAXIES IN COMA CLUSTER MAY BE PACKED WITH DARK MATTER
RAS
Galaxies in a cluster roughly 300 million light-years away could
contain as much as 100 times more dark matter than visible matter,
according to an Australian study. The research used computer
simulations to study galaxies that have fallen into the Coma Cluster,
one of the largest structures in the Universe, in which thousands of
galaxies are bound together by gravity. It found that the galaxies
could have fallen into the cluster as early as seven billion years
ago, which, if current theories of galaxy evolution are correct,
suggests that they must have lots of dark matter protecting the
visible matter from being dispersed by the cluster. Dark matter
cannot be seen directly but the substance is thought by some to make
up about 84% of the matter in the Universe. The galaxies studied in
the Coma Cluster are about the same size as our own Milky Way but
contain only about a hundredth as many stars. The galaxies appear to
have stopped making new stars when they first fell into the cluster
and have been dead ever since, leading astrophysicists to label them
'failed' galaxies. Galaxies form when large clouds of hydrogen gas
collapse and are converted to stars; if that gas is removed, the
galaxy cannot grow further. Falling into a cluster is one way in
which that can happen. The gravitational field of the cluster pulls
in the galaxy, but its gas is pushed out and in effect is stolen by
hot gas in the cluster itself.
MASSIVE FLARE FROM BLACK HOLE IN DISTANT GALAXY
NASA/Goddard Space Flight Center
Five billion years ago, a great disturbance rocked a region near the
black hole at the centre of galaxy 3C 279. On June 14, the pulse of
high-energy light produced by that event finally arrived here, setting
off detectors aboard the Fermi gamma-ray satellite and other
satellites. Astronomers turned their instruments toward the galaxy to
observe the brief but record-setting flare in greater detail. One day
3C 279 was just one of many active galaxies we see; the next day it
was the brightest object in the gamma-ray sky. 3C 279 is a famous
blazar, a galaxy whose high-energy activity is powered by a central
super-massive black hole of up to a billion times the Sun's mass and
roughly the size of our planetary system. As matter falls toward
the black hole, some particles race away at nearly the speed of light
along a pair of jets pointing in opposite directions. What makes a
blazar so bright is that one of the particle jets happens to be aimed
almost straight at us. The 3C 279 flare is the most dynamic outburst
Fermi has seen in its seven years of operation, becoming 10 times
brighter overnight. Astronomers think that some change within the jet
was responsible for the flare, but they have not suggested *what*
change..
The brightest persistent source in the gamma-ray sky is the Vela
pulsar, which is about 1,000 light-years away. 3C 279 is millions of
times farther off, but during the flare it became four times brighter
than Vela. That corresponds to a tremendous energy release, and one
that could not be sustained for long. The galaxy dimmed to normal
gamma-ray levels by June 18. The rapid fading is why astronomers
rush to collect data as soon as they detect a blazar flare. The
priority is to make observations while the object is still bright.
Once it is over, we can start trying to understand the mechanisms
powering it. The Italian AGILE gamma-ray satellite first reported the
flare, followed by Fermi. Rapid follow-up observations were made by
the Swift satellite and the ESA INTEGRAL spacecraft, which just
happened to be looking in the right direction, along with optical and
radio telescopes on the ground. 3C 279 holds a special place in the
history of gamma-ray astronomy. During a flare in 1991 detected by
the EGRET instrument on the then-recently-launched Compton gamma-ray
observatory, the galaxy set the record for the most distant and
luminous gamma-ray source known at the time. The June 14 outburst
rapidly brightened in less than a day and peaked on June 16, producing
a gamma-ray flare 10 times brighter than the 1991 event. The rapidity
of the variations conveys information about the size of the emitting
region, which cannot be larger than the distance that light can travel
during the flare.
ARCHIVE DATA REVEAL CLUES ABOUT BLACK HOLES' DIET
RAS
Using archival data from the Sloan Digital Sky Survey, and the XMM-
Newton and Chandra X-ray telescopes, a team of astronomers has
discovered a gigantic black hole, which is probably destroying and
devouring a big star in its vicinity. With a mass of 100 million
Suns, that is the largest black hole caught in such an act so far.
The team was exploring the Sloan Digital Sky Survey (SDSS) in
preparation for a future X-ray satellite mission. The SDSS has been
observing a large fraction of the night sky with its optical
telescope. In addition, spectra, allowing astronomers to deduce
properties like composition and temperature, have been taken of
distant galaxies and black holes. Some objects had their spectra
taken more than once, and the team was struck by an extraordinary
change in one of the objects under study, with the catalogue number
SDSS J0159+0033, a galaxy in the constellation of Cetus. The huge
distance to the galaxy means that we see it as it was 3.5 billion
years ago. Usually, distant galaxies do not change significantly over
an astronomer's lifetime, but that one showed a dramatic variation of
its spectrum, as if the central black hole had switched on and off.
That happened between 1998 and 2005, but nobody had noticed the odd
behaviour of that galaxy until late last year, when two groups of
scientists preparing the next (fourth) generation of SDSS surveys
independently stumbled across the data.
Fortunately, two X-ray observatories, XMM-Newton and Chandra, observed
that area of the sky close in time to the peak of the flare, and again
about ten years later. That gave the astronomers information about
the high-energy emission that reveals how material is processed in the
immediate vicinity of the central black hole. Gigantic black holes
are found in the nuclei of large galaxies all around us. Most
astronomers believe that they grew to the enormous sizes that we
observe today by feeding mostly on interstellar gas from their
surroundings. Such a process takes place over a very long time (tens
to hundreds of millions of years), and is capable of turning a small
black hole created in the explosion of a heavy star into the super-
massive monsters that lurk at the centres of galaxies. However,
galaxies also contain huge numbers of stars. Some unlucky ones may
happen to pass too close to the central black hole, where they are
destroyed and subsequently bits and pieces swirl into the black hole
and thus produce huge flares of radiation that can be as luminous as
all the rest of the stars in the host galaxy together for a period of
a few months to a year. Those rare events are called 'tidal disruption
flares'. The team quickly realized that 'its' flare matched almost
perfectly the expectations of that model.
ASSEMBLY OF GALAXIES IN EARLY UNIVERSE
ESO
The ALMA millimetre-wave array has been used to detect the most
distant clouds of star-forming gas yet found in normal galaxies in the
early Universe. The new observations allow astronomers to start to
see how the first galaxies were built up and how they cleared the
cosmic fog during the era of re-ionization. This is the first time
that such galaxies are seen as more than just faint blobs. When the
first galaxies started to form, a few hundred million years after the
Big Bang, the Universe was full of a fog of hydrogen gas. But as more
and more brilliant sources -- both stars and quasars powered by huge
black holes -- started to shine, they cleared away the fog and made
the Universe transparent to ultraviolet light. Astronomers call that
the 'epoch of re-ionization', but little is known about those first
galaxies. A team of astronomers trained ALMA on galaxies that were
known to be seen only about 800 million years after the Big Bang. The
astronomers were not looking for the light from stars, but instead for
the faint glow of ionized carbon coming from the clouds of gas from
which the stars were forming. They wanted to study the interaction
between a young generation of stars and the cold clumps that were
assembling into those first galaxies. They were also not looking for
the extremely brilliant rare objects -- such as quasars and galaxies
with very high rates of star formation -- that had been seen up to
now. Instead they concentrated on rather less dramatic, but much more
common, galaxies that re-ionized the Universe and went on to turn into
the bulk of the galaxies that we see around us now.
From one of the galaxies -- given the label BDF 3299 -- ALMA could
pick up a faint but clear signal from the glowing carbon. However,
the glow was not coming from the centre of the galaxy, but rather from
one side. The astronomers think that the off-centre location of the
glow is because the central clouds are being disrupted by the harsh
environment created by the newly formed stars -- both their intense
radiation and the effects of supernova explosions -- while the carbon
glow is tracing fresh cold gas that is being accreted from the
intergalactic medium. By combining the new ALMA observations with
computer simulations, it has been possible to imagine in detail key
processes occurring within the first galaxies. The effects of the
radiation from stars, the survival of molecular clouds, the escape of
ionizing radiation and the complex structure of the interstellar
medium can now be calculated and compared with observation. BDF 3299
is likely to be a typical example of the galaxies responsible for
re-ionization.
Topic: Early August Astronomy Bulletin (Read 1396 times)