Topic: Late May Astronomy Bulletin

[Clive]

THIRD-LARGEST DWARF PLANET HAS MOON
NASA/Goddard Space Flight Center

The combined power of three space observatories, including the
Hubble Space Telescope, has helped astronomers discover a moon
orbiting the third-largest dwarf planet, catalogued as 2007 OR10.
The pair resides in the frigid outskirts of the Solar System
called the Kuiper Belt, a realm of icy debris left over from the
system's formation 4600 million years ago.  With this discovery,
most of the known dwarf planets in the Kuiper Belt larger than
600 miles across have companions.  Those bodies provide insight
into how moons formed in the young Solar System.  The discovery
of satellites around all of the known large dwarf planets (except
for Sedna) means that, when those bodies formed, a very long time
ago, collisions must have been more frequent, and that is a
constraint on the formation models.  If there were frequent
collisions, then it was quite easy to form satellites.  The
objects most likely slammed into one another more often because
they inhabited a crowded region.  But the speed of the colliding
objects could not have been too fast or too slow, according to
the astronomers.  If the impact velocity were too great, the
smash-up would have created lots of debris that could have
escaped from the system; if too slow, the collision would have
produced only an impact crater.

The team discovered the moon in archival images of 2007 OR10
taken by Hubble's Wide-Field Camera 3.  Observations taken of the
dwarf planet by the Kepler space telescope first tipped off the
astronomers to the possibility of a moon circling it.  Kepler
revealed that 2007 OR10 has a slow rotation period of 45 hours.
Typical rotation periods for Kuiper-Belt Objects are under 24
hours.  The team looked in the Hubble archive because the slower
rotation period could have been caused by the gravitational
effect of a moon.  The initial investigator missed the moon in
the Hubble images because it is very faint.  The astronomers
observed the moon in two separate Hubble observations spaced a
year apart.  The images show that the moon is gravitationally
bound to 2007 OR10 because it moves with the dwarf planet, as
seen against a background of stars.  However, the two observa-
tions did not provide enough information for the astronomers to
determine an orbit.  They calculated the diameters of both
objects on the basis of observations in far-infrared light by
the Herschel Space Observatory, which measured their thermal
emission.  The dwarf planet is about 950 miles across, and its
moon is estimated to be 150--250 miles in diameter.  2007 OR10,
like Pluto, follows an eccentric orbit, and is currently three
times farther from the Sun than Pluto is.  2007 OR10 is a member
of the exclusive club of 'dwarf planets', of which there are
nine.  Of those bodies, only Pluto and Eris are larger.


'DETERGENT' MOLECULES MAY DRIVE METHANE CHANGES 
NASA

A new study finds that recent increases in global methane levels
observed since 2007 are not necessarily due to increasing
emissions, but instead may be due to changes in how long methane
remains in the atmosphere after it is emitted.  The second-most-
important human-produced greenhouse gas after carbon dioxide,
methane is colourless, odourless and can be hard to track.  The
gas has a wide range of sources, from decomposing biological
material to leaks in natural-gas pipelines.  In the early 2000s,
atmospheric scientists studying methane found that its global
concentration -- which had increased for decades, driven by
methane emissions from fossil fuels and agriculture -- levelled
off as the sources of methane reached a balance with its
destruction mechanisms.  The methane levels remained stable for a
few years, then unexpectedly started rising again in 2007, a
trend that is still continuing.  Previous studies of the renewed
increase have focused on high-latitude wetlands or fossil fuels,
Asian agricultural growth, or tropical wetlands as potential
sources of the increased emissions.  But the new study suggests
that methane emissions might not have increased dramatically
since 2007 after all.

The researchers used long-term measurements of methane, its
isotopes and 1,1,1-trichloroethane (a compound that serves as a
proxy for estimating how long methane remains in the atmosphere)
from numerous global ground stations.  From those data, the
scientists were able to determine sources of methane and how
quickly it is destroyed in the Earth's atmosphere. They found
that the most likely explanation for the recent increase has less
to do with methane emissions than previously thought and more to
do with changes in the availability of the hydroxyl radical (OH),
which breaks down methane in the atmosphere.  The amount of
hydroxyl in the atmosphere has an impact on global methane
concentrations.  If global levels of hydroxyl decrease, global
methane concentrations will increase -- even if methane emissions
remain constant.  In tracking the observed changes in methane and
the inferred changes in hydroxyl, scientists noted that fluctua-
tions in hydroxyl concentrations can explain some of the recent
methane trends.  However, the scientists cannot explain the
global changes in hydroxyl concentrations seen in the past
decade.  They say that future independent studies are needed to
quantify year-to-year variations in the hydroxyl radical and
their potential drivers.  They would also like to see the trends
they detected verified with more detailed studies of the sources
and the destruction mechanisms of methane, particularly in the
tropics.


A FAR-FLUNG MEMBER OF THE SOLAR SYSTEM
National Radio Astronomy Observatory

Using the Atacama Large Millimeter/submillimeter Array (ALMA),
astronomers have obtained extraordinary details about a recently
discovered far-flung member of the Solar System, the planetary
body 2014 UZ224, informally known as DeeDee.  At about three
times the current distance of Pluto from the Sun, DeeDee is the
second-most-distant-known trans-Neptunian object (TNO) with a
confirmed orbit, surpassed only by the dwarf planet Eris.
Astronomers estimate that there are tens of thousands of such icy
bodies in the outer Solar System beyond the orbit of Neptune.
The new ALMA data reveal, for the first time, that DeeDee is
roughly 635 kilometres across, or about two-thirds the diameter
of Ceres, the largest member of the asteroid belt.  At that size,
DeeDee should have enough mass to be spherical, the criterion
necessary for astronomers to consider it to be a dwarf planet,
though it has yet to receive that official designation.
Currently, DeeDee is about 92 astronomical units (AU) from the
Sun.  It takes DeeDee more than 1,100 years to complete one
orbit; light from DeeDee takes nearly 13 hours to reach the
Earth. 

The object was discovered with the 4-metre Blanco telescope at
the Cerro Tololo Inter-American Observatory in Chile as part of
ongoing observations for the 'Dark Energy Survey', that seeks to
understand the accelerating expansion of the Universe.  The Dark
Energy Survey produces vast numbers of astronomical images, which
give astronomers the opportunity to search also for distant
Solar-System objects.  The initial search, which includes nearly
15,000 images, identified more than a thousand million candidate
objects. The vast majority of them turned out to be background
stars and even-more-distant galaxies.  A small fraction, however,
were observed to move slowly across the sky over successive
observations, the telltale sign of a TNO.

One such object was identified on 12 separate images.  The
astronomers informally dubbed it DeeDee, which is short for
Distant Dwarf.  The optical data from the Blanco telescope
enabled the astronomers to measure DeeDee's distance and orbital
properties, but they were unable to determine its size or other
physical characteristics.  It was possible that DeeDee was a
relatively small member of the Solar System, yet reflective
enough to be detected.  Alternatively, it could be uncommonly
large and dark, reflecting only a tiny portion of the feeble
sunlight that reaches it; both scenarios would produce identical
optical data.  Since ALMA observes the cold, dark Universe, it is
able to detect the heat -- in the form of millimetre-wavelength
radiation -- emitted naturally by cold objects in space.  The
heat signature from a distant Solar-System object would be
directly proportional to its size.  By comparing the ALMA
observations to the earlier optical data, the astronomers had the
information necessary to calculate the object's size.  Objects
like DeeDee are cosmic leftovers from the formation of the Solar
System.  Their orbits and physical properties reveal important
details about the formation of planets, including the Earth.
This discovery shows that it is possible to detect very distant,
slowly moving objects in the Solar System.  The researchers note
that the same technique might be used to detect the hypothesized
'Planet Nine' that may reside far beyond DeeDee and Eris.


STUDY SHOWS MOST HABITABLE PLANETS LACK DRY LAND
RAS
 
A new study has used a statistical model to suggest that most
habitable planets may be dominated by oceans spanning over 90% of
their surface area.  The author of the study has constructed a
statistical model -- based on Bayesian probability -- to predict
the division between land and water on habitable exo-planets.
For a planetary surface to have extensive areas of both land and
water, a delicate balance must be struck between the volume of
water it retains over time, and how much space it has to store it
in its oceanic basins.  Both of those quantities may vary
substantially across the full spectrum of water-bearing worlds,
and why the Earth's values are so well balanced is an unresolved
and long-standing conundrum.  The model predicts that most
habitable planets will be dominated by oceans spanning over 90%
of their surface areas.  That conclusion is reached because the
Earth itself is close to being a so-called 'water world' - a
world where all land is immersed under a single ocean.  The new
work finds that the Earth's finely balanced oceans may be a
consequence of the 'anthropic principle' -- more often used in a
cosmological context -- which accounts for how our observations
of the Universe are influenced by the requirement for the
formation of sentient life.  On the basis of the Earth's ocean
coverage of 71%, there is evidence supporting the hypothesis that
anthropic selection effects are at work.

To test the statistical model, feedback mechanisms were taken
into account, such as the deep-water cycle and erosion and
deposition processes.  The study also proposes a statistical
approximation to determine the diminishing habitable land area
for planets with smaller oceans as they become increasingly
dominated by deserts.  Why did we evolve on this planet and not
on one of the many other habitable worlds?  In this study it is
suggested that the answer could be linked to a selection effect
involving the balance between land and water.  Our understanding
of the development of life is far from complete, but it is not
quite so dire that we must adhere to the approximation that all
habitable planets have an equal chance of hosting intelligent
life.
 
 
SUPER-MASSIVE BLACK HOLES FOUND IN TINY GALAXIES
University of Utah

Three years ago, astronomers discovered that an ultra-compact
dwarf galaxy contained a super-massive black hole, then the
smallest known galaxy to harbour such a giant black hole.  The
findings suggested that the dwarfs were probably tiny leftovers
of larger galaxies that were stripped of their outer layers after
colliding into other, still larger galaxies.  Now, the same group
of astronomers has found two more ultra-compact dwarf galaxies
with super-massive black holes. Together, the three examples
suggest that black holes may lurk at the centres of most of such
objects, potentially doubling the number of super-massive black
holes known in the Universe.  The black holes make up a high
percentage of the compact galaxies' total mass, supporting the
idea that the dwarfs are remnants of massive galaxies that were
ripped apart by larger galaxies.  The team measured two ultra-
compact dwarf galaxies, named VUCD3 and M59cO, that orbit massive
galaxies in the Virgo galaxy cluster.  They detected a super-
massive black hole in both galaxies; VUCD3's black hole has a
mass equivalent to 4.4 million Suns, making up about 13% of the
galaxy's total mass, and M59cO's black hole has a mass of 5.8
million Suns, making up about 18% of its total mass.  For
comparison, the monstrous black hole at the centre of the Milky
Way has a mass of 4 million Suns, but makes up less than .01%
of our Galaxy's total mass.

To calculate the ultra-compact dwarf galaxies' mass, the
astronomers measured the movements of the stars with the Gemini
North telescope on Mauna Kea.  They used adaptive optics to
reduce the distortions caused by the Earth's atmosphere.  They
also analyzed images from the Hubble Space Telescope to measure
the distribution of the stars in each galaxy, and used computer
simulations to fit their observations.  They found that the stars
at the centres of the galaxies moved much faster than those on
the outside, a classic signature of a black hole.


BRIDGE OF DARK-MATTER WEB IMAGED 
RAS
 
Researchers at the University of Waterloo have been able to
capture the first composite image of a dark-matter bridge that
connects galaxies together.  The composite image, which combines
a number of individual images, confirms predictions that galaxies
across the Universe are tied together through a cosmic web con-
nected by dark matter that has until now remained unobservable.
Dark matter, a mysterious substance that comprises around 25 per
cent of the Universe, does not shine, absorb or reflect light,
which has made it largely undetectable, except through gravity.
For decades, researchers have been predicting the existence of
dark-matter filaments between galaxies that act as a web-like
superstructure connecting galaxies together.  The new image moves
us beyond predictions to something that we can see and measure.
As part of their research, astronomers used a technique called
weak gravitational lensing, an effect that causes the images of
distant galaxies to warp slightly under the influence of an
unseen mass such as a planet, a black hole, or in this case, dark
matter.  The effect was measured in images from a multi-year sky
survey at the Canada-France-Hawaii Telescope.  They combined
lensing images from more than 23,000 galaxy pairs located 4500
million light-years away to create a composite image or map that
shows the presence of dark matter between the pairs of galaxies.
Results show the dark-matter filament bridge is strongest between
systems less than 40 million light-years apart.  By using that
technique, researchers are not only able to see that the dark-
matter filaments in the Universe exist, but are also able to see
the extent to which the filaments connect galaxies together.


COLD SPOT MAY INDICATE ANOTHER UNIVERSE
RAS
 
A super-void is unlikely to explain a 'Cold Spot' in the cosmic
microwave background, according to the results of a new survey,
leaving room for exotic explanations like a collision between
universes, according to researchers from Durham University's
Centre for Extragalactic Astronomy.  The cosmic microwave
background (CMB), a relic of the Big Bang, covers the whole sky.
At a temperature of 2.73 degrees above absolute zero (or -270.43
degrees C), the CMB has some anomalies, including the Cold Spot.
That feature, about 0.00015 degrees colder than its surroundings,
was previously claimed to be caused by a huge void, millions of
light-years across, containing relatively few galaxies.  The
accelerating expansion of the Universe causes voids to leave
subtle redshifts on light as it passes through, owing to the
'integrated Sachs-Wolfe effect'. In the case of the CMB that is
observed as cold imprints.  It was proposed that a very large
foreground void could, in part, imprint the CMB Cold Spot which
has been a source of tension in models of standard cosmology.
Previously, most searches for a super-void connected with the
Cold Spot have estimated distances to galaxies from their
colours.  With the expansion of the Universe, galaxies have their
light reddened by the cosmological redshift.  The more distant
the galaxy is, the higher its observed redshift.  By measuring
the colours of galaxies, their redshifts, and thus their
distances, can be estimated, though with a high degree of
uncertainty.
 
In the new work, the Durham team presents the results of a
comprehensive survey of the redshifts of 7,000 galaxies,
harvested 300 at a time with a spectrograph deployed on the
Anglo-Australian Telescope.  From that data set, the team sees no
evidence of a super-void capable of explaining the Cold Spot
within the standard theory.  The researchers instead found that
the Cold Spot region, previously thought to be under-populated
with galaxies, is split into smaller voids, surrounded by
clusters of galaxies.  That 'soap-bubble' structure is much like
the rest of the Universe, illustrated by the visual similarity
between the galaxy distributions in the Cold Spot area and a
control field elsewhere.  The voids cannot explain the Cold Spot
under standard cosmology.  There is a possibility that some non-
standard model could be proposed to link the two in the future,
but the data place powerful constraints on any attempt to do
that.  If there really is no super-void that can explain the Cold
Spot, simulations of the standard model of the Universe give odds
of 1 in 50 that the Cold Spot arose by chance.  That means that
we can not rule out the possibility that the Spot is caused by a
statistical fluctuation explicable by the standard model.  But if
that is not the answer, then there are more exotic explanations.
Perhaps the most extreme of those is that the Cold Spot was
caused by a collision between our Universe and another 'bubble
Universe'.  If further, more detailed, analysis of CMB data were
to prove that to be the case, then the Cold Spot might be taken
as the first evidence for the multiverse -- and millions of other
universes like our own might exist.  But that is rather 'building
castles in the air': for the moment, the most that can safely be
said is that the lack of a super-void to explain the Cold Spot
has tilted the balance towards more unusual explanations, ideas
that will need to be tested by more detailed observations of the
CMB.