The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 375 2014 May 4
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online at
our secure site and can take credit and debit cards. You can join or
renew via a secure server or just see how much we have to offer by
visiting http://www.popastro.com/ CONNECTIONS WITH NOCTILUCENT CLOUDS [?]
NASA Data from the AIM spacecraft (described below) have been interpreted
as indicating 'teleconnections' in the Earth's atmosphere that stretch
from the North Pole to the South Pole and back again, linking weather
and climate more closely than simple geography would suggest. For
example, scientists have found that the winter air temperature in
Indianapolis, Indiana, is well correlated with the frequency of
noctilucent clouds over Antarctica. Noctilucent clouds (NLCs) are the
highest type of cloud. They form at the edge of space, 83 km above
the polar regions, in a layer called the mesosphere. Seeded by
'meteor smoke', NLCs are made of tiny ice crystals that glow electric
blue in sunlight. AIM was launched in 2007 to investigate NLCs, to discover how they
form and to learn about their chemistry. As is often the case,
however, when exploring the unknown, researchers found something they
weren't looking for -- teleconnections. When the AIM mission was
being planned, attention was focused on a narrow layer of the
atmosphere where NLCs form. Now scientists are finding that the layer
manifests evidence of long-distance connections in the atmosphere far
from the NLCs themselves. One connection links the Arctic
stratosphere with the Antarctic mesosphere. Stratospheric winds over
the Arctic control circulation in the mesosphere. When northern
stratospheric winds slow down, a ripple effect around the globe causes
the southern mesosphere to become warmer and drier, leading to fewer
NLCs. When northern winds pick up again, the southern mesosphere
becomes colder and wetter, and the NLCs return. This January, a time of year when southern NLCs are usually abundant,
the spacecraft observed a sudden decline in the clouds. About two
weeks earlier, winds in the Arctic stratosphere were strongly
perturbed, leading to a distorted polar vortex. It is *believed* that
that triggered a ripple effect that led to a decline in noctilucent
clouds half-way round the world. The same polar vortex made headlines
in the USA last winter when parts of that country experienced unusual
cold. Researchers found that there was indeed a statistical link
between winter weather in the USA and the decline in noctilucent
clouds over Antarctica. In many northern US cities cold air
temperatures on the ground were correlated with NLC frequencies high
above Antarctica two weeks later. The two-week delay is, apparently,
the time it takes for a signal to propagate through three layers of
atmosphere (the troposphere, stratosphere and mesosphere), and from
pole to pole. [Note by editor: The above item alleges a seemingly improbable
statistical correlation, for which no plausible mechanism is
suggested, that involves a fortnight's delay. If the alleged
correlation really exists, the delay provides an opportunity to test
its reality by forecasting Antarctic NLC frequencies a fortnight in
advance from the weather experienced in the USA. It would have been
so easy to make such a simple and obvious test of what is being
alleged that one might expect that it would have been undertaken and
its results described before this item was rushed into print. It is
easy to look for, and sometimes to find, temporary apparent
correlations between things that can not really be connected at all.
There are so many different things that one can try to correlate that
it is inevitable that there will be coincidental 'successes' from time
to time. I remember seeing on one occasion a supposedly convincing
correlation between the appearance of new large sunspots and the dates
of matinees of the Folies Bergere! But when the next season's
programme was to hand and the dates of matinees known, those dates
ought to have been (but weren't, as far as I know) promulgated to
astronomers as forecasts of the dates of appearance of new large
sunspots. No doubt that was hardly worth doing, since the forecasts
would have been bound to fail. If the correlation had held up season
after season I feel sure that we should have heard a lot more about it
by now.]
POSSIBLE NEW MOON FORMING AROUND SATURN
NASA The Cassini spacecraft has documented the formation of a small icy
object within the rings of Saturn. Astronomers think they may be
looking at the act of birth, where this object is just leaving the
rings and heading off to be a moon in its own right. Images taken
with Cassini's narrow-angle camera on 2013 April 15 show disturbances
at the very edge of Saturn's A ring -- the outermost of the planet's
large, bright rings. One of the disturbances is an arc about 20%
brighter than its surroundings, 1200 km long and 10 km wide.
Scientists also found unusual protuberances in the usually smooth
profile at the ring's edge, and believe that the arc and protuberances
are caused by the gravitational effects of a nearby object. The
object is not expected to grow any larger, and may even be falling
apart. Cassini's orbit will move closer to the outer edge of the A ring in
late 2016 and provide an opportunity to study the postulated object,
which is too small to see in images so far; it is estimated to be no
more than about a kilometre in diameter. Saturn's icy moons range in
size more or less according to their proximity to the planet -- the
farther from the planet, the larger. And many of Saturn's moons are
comprised primarily of ice, as are the particles that form Saturn's
rings. Researchers recently speculated that the icy moons formed from
ring particles and then moved outward, away from the planet, merging
with other moons on the way. The theory holds that Saturn long ago
had a much more massive ring system capable of giving birth to larger
moons. As the moons formed near the edge, they depleted the rings.
It is possible that the process of moon formation in Saturn's rings
has ended with this object, as Saturn's rings now are, in all
likelihood, too depleted to make more moons. [Note by editor: Received wisdom used to be exactly the reverse of
what is now being suggested: it was that the rings are the debris of
satellites that were tidally disrupted by Saturn when they approached
within the Roche limit. That idea did at least provide a plausible
origin for the rings, whereas the item above seems to take the rings
for granted as being just a natural source of material for the
manufacture of new satellites, without any concern for how the
material got there in the first place. And the cheerful way in which
unidentified astronomers are said to suggest that a moon can form and
then be "just leaving the rings and heading off to be a moon in its
own right", as if it had its own motor, could choose its own
itinerary, and could just go where it likes without there being any
dynamical reason that would make its path differ from the paths of the
rest of the ring particles, hardly inspires confidence in any
scientific underpinning that there may be for this report.]
NEARBY STAR DISCOVERED
NASA The Wide-field Infrared Survey Explorer (WISE) and Spitzer Space
Telescope have discovered what appears to be the coldest brown dwarf
known -- a dim, star-like body that, surprisingly, is as frosty as the
Earth's North Pole. Named WISE J085510.83-071442.5, the brown dwarf
appears to be 7.2 light-years away, making it the fourth-closest
system to us. It has a temperature between -48 and -13°C. Previous
record-holders for the coldest brown dwarfs, also found by WISE and
Spitzer, were about room temperature. WISE was able to spot the
object because it surveyed the entire sky twice in infrared light.
Cool objects like brown dwarfs can be invisible when viewed by
visible-light telescopes, but their thermal glow -- even if feeble --
stands out in infrared light. In addition, the closer a body, the
more it may appear to move in images taken months apart. After
noticing the fast motion of the WISE object, astronomers spent time
analyzing additional images taken with Spitzer and the Gemini South
telescope in Chile. Spitzer's infrared observations helped determine
the temperature of the brown dwarf. Combined detections from WISE and
Spitzer, taken from different positions around the Sun, gave the
object's parallax, and thus its distance. The WISE object with the long name appears to be 3 to 10 times the
mass of Jupiter. With such a low mass, it could be a gas giant
similar to Jupiter that was ejected from its star system. But
scientists think [this is what the item says; I am not making it up --
ED.] it is probably a brown dwarf rather than a planet, on the
[remarkably weak] grounds that brown dwarfs are known to be fairly
common. If so, it is one of the least-massive brown dwarfs known.
A NEARBY PLANETARY SYSTEM
RAS 55 Cancri is a star bright enough to be seen with the naked eye, with
a planetary system. Its radial velocity has been measured at four
different observatories over a thousand times in total, giving the
planets in that system much more attention than most exo-planets
receive. Astronomers first discovered that 55 Cancri is orbited by a
giant planet in 1997. Long-term observations later detected five
planets orbiting the star, ranging from a cold giant planet with an
orbit very similar to that of Jupiter to a scorching-hot "super-Earth"
-- a type of planet with a mass more than the Earth's but much less
than that of Neptune, which has a mass 17 times greater than the
Earth's. Numerous studies since 2002 had failed to identify a plausible model
for the masses and orbits of two giant planets located closer to 55
Cancri than Mercury is to the Sun. Astronomers had struggled to
understand how those massive planets orbiting so close to their star
could avoid a catastrophe such as one planet being flung into the
star, or the two planets colliding with each other. Now, a new study
led by Pennsylvania State University has combined thousands of
observations with new statistical and computational techniques to
measure the planets' properties more accurately, showing that their
particular masses and orbits are preventing the system from
self-destructing at all soon. The 55 Cancri planetary system is
unique both in the diversity of its known planets and the number and
variety of astronomical observations. The complexity of the system
makes it unusually challenging to interpret the observations. In
order to perform the new analyses, astronomers collaborated with
computer scientists to develop a tool for simulating planetary systems
using graphics cards to accelerate the computations. By combining
multiple types of observations, the Penn State astronomers determined
that one of the planets in the system (55 Cnc e) has eight times the
Earth's mass, twice the Earth's radius, and thus the same mean density
as the Earth. The planet is far too hot to have liquid water, as its
surface temperature is estimated to be 2100°C. It was only in 2011,
8 years after the discovery of 55 Cnc e, that astronomers recognised
that it orbits its star in less than 18 hours, rather than nearly
3 days, as originally thought. Soon after, astronomers detected the
planet in transit in front of the star, allowing them to measure the
relative size of the planet too. The two giant planets of 55 Cancri interact so strongly that we can
detect changes in their orbits. The rapid interactions between the
planets present a challenge, since modelling the system requires time-
consuming simulations for each model to determine the trajectories of
the planets and therefore the likelihood of their survival for
billions of years without a catastrophic collision. One must account
precisely for the motions of the giant planets in order to measure the
properties of the super-Earth-mass planet. Most previous analyses had
ignored the planet-planet interactions. A few earlier studies had
modelled those effects, but had performed only simplistic statistical
analyses owing to the huge number of calculations required for a
proper analysis.
HOW BLACK HOLES SHAPE GALAXIES
RAS The Universe we can see is made up of billions of galaxies, each
containing anywhere from hundreds of thousands to hundreds of billions
of stars. Large numbers of galaxies are elliptical in shape, red and
mostly made up of old stars. Another (more familiar) type is the
spiral, where arms wind out in a blue thin disc from a central red
bulge. On average stars in spiral galaxies tend to be much younger
than those in ellipticals. Now a group of astronomers has found a
(relatively) simple relationship between the colour of a galaxy and
the size of its bulge -- the more massive the bulge the redder the
galaxy. The team used data from the Sloan Digital Sky Survey to group
together over half a million galaxies of all different colours,
shapes, and masses. They then used pattern-recognition software to
measure the shape of each one, to see how the proportion of red stars
in a galaxy varies with its other properties. They found that the
mass in the central bulge (regardless of how big the disc surrounding
it may be) is the key to knowing the colour of the whole galaxy.
Above a given bulge mass, galaxies are red and have no new young
stars. Almost all galaxies have massive black holes at their centres.
The mass of the bulge is closely related to the mass of the black
hole; the more massive the black hole the more energy is released into
the surrounding galaxy in the form of powerful jets and X-ray
emission, which can blow away and heat up gas, stopping new stars from
forming. Thus a relatively simple result, that large galaxy bulges
mean red galaxies, has profound consequences: big bulges mean big
black holes, which can put an end to star formation.
Bulletin compiled by Clive Down (c) 2014 the Society for Popular Astronomy
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