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The SOCIETY for POPULAR ASTRONOMY

Electronic News Bulletin No. 403 2015 July 19

Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is arguably 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/




IRREGULAR HEARTBEAT OF SUN
RAS

A new model of the solar cycle is producing accurate predictions
of irregularities within the Sun's 11-year cycle. The model draws on
dynamo effects in two layers of the Sun, one close to the surface and
one deep within its convection zone. Predictions from the model
suggest that solar activity will fall by 60 per cent during the 2030s
to conditions last seen during the 'mini ice age' that began in 1645.
It is 172 years since a scientist first noticed that the Sun's
activity varies over a cycle lasting around 10 to 12 years. But every
cycle is a little different, and none of the models of causes to date
has fully explained the fluctuations. Many solar physicists have
attributed the solar cycle to a dynamo caused by convecting fluid
deep within the Sun. Now, astronomers have found that adding a second
dynamo, close to the surface, completes the picture with surprising
accuracy. The researchers found magnetic wave components appearing in
pairs, originating in two different layers in the Sun's interior.
They both have a frequency of approximately 11 years, although their
frequencies are slightly different, and they are offset in time. Over
the cycle, the waves fluctuate between the northern and southern
hemispheres of the Sun. When the two waves were combined and compared
with real data for the current solar cycle, their predictions showed
an accuracy of 97%.

The team derived its model by a technique called 'principal component
analysis' of the magnetic-field observations from the Wilcox Solar
Observatory in California. They examined three solar cycles' worth of
magnetic-field activity, covering the period 1976-2008. In addition,
they compared the predictions with average sunspot numbers, another
strong marker of solar activity. All the predictions and observations
were closely matched. Looking ahead to the next solar cycles, the
model predicts that the pair of waves become increasingly offset
during Cycle 25, which peaks in 2022. During Cycle 26, which covers
the decade 2030-2040, the two waves will become exactly out of sync,
and that will cause a significant reduction in solar activity. In
cycle 26, the two waves exactly mirror each other -- peaking at the
same time but in opposite hemispheres of the Sun. Their interaction
will be disruptive -- they will nearly cancel one another. The team
predicts that that will lead to the properties of a 'Maunder minimum'.
Effectively, when the waves are approximately in phase, they can show
strong reinforcement, or resonance, and we have strong solar activity.
When they are out of phase, we have solar minimum. When there is full
phase separation, we have the conditions last seen during the Maunder
minimum, 370 years ago.


NEW HORIZONS AT PLUTO
BBC News

Now that the New Horizons probe has successfully flown past Pluto and
confirmed that it is all in one piece, researchers can look forward to
a cornucopia of images and data from the strange, distant world over
the next 16 months. But even though only a few of pictures have been
transmitted so far, scientists are learning more from them than they
have in years of telescopic observations. For 60 years scientists
have known that there was a bright mass on Pluto, but it was only the
high resolution provided by the cameras on New Horizons that detailed
its distinctive heart shape which is believed to have been caused by
an impact. Researchers believe that the crater is filled with frozen
gases from the atmosphere -- nitrogen, methane and carbon dioxide.
The initial image had a reddish hue, something that scientists have
long known. It is very different from the other red planet, Mars,
in that Pluto's colour is probably caused by hydrocarbon molecules,
called tholins, that are formed when solar ultraviolet light and
cosmic rays interact with methane in Pluto's atmosphere and on its
surface. Pluto's reddening process occurs even on the night side
where there is no sunlight, and in the depths of winter when the Sun
remains below the horizon for decades at a time.

New Horizons has provided more accurate information on the size of
Pluto. It is slightly (about 80 km) bigger than expected, making it
around two-thirds the size of our Moon. The increased dimensions mean
that Pluto is likely to be made of less rock and more ice beneath its
surface, according to members of the mission team. The revision makes
Pluto now officially bigger than Eris, one of hundreds of thousands
of mini-planets and comet-like objects circling beyond Neptune in a
region called the Kuiper Belt. The relative lack of impact craters on
Pluto could be an indication that the surface is being renewed, either
by internal or atmospheric activity, such as erosion. There is
evidence of surface activity, a tantalizing hint of Earth-like
tectonics in its past or even its present. NASA has dubbed one of the
strange, darker regions of Pluto the 'whale'. Researchers say it is
unusual to have contrasting bright and dark surfaces on objects in our
Solar System, reflecting the fact that Pluto is far more complex than
previously thought. Surface temperatures on Pluto are extremely cold,
ranging from -172 to -238 degrees C depending on where it is in its
248-year orbit of the Sun. Since it passed perihelion in 1989,
experts assumed that since then it should have been cooling. Pluto
has strong atmospheric cycles: it snows on the surface, and then the
snow sublimates and goes back into the atmosphere in the course of
each 248-year orbit. Little light has so far been shed on the moons
of Pluto, but an image indicates that Charon, the biggest, is covered
with red material around its pole. Scientists believe that that stuff
may be tholins that have escaped from Pluto's atmosphere. Experts
believe that the mottled colours at lower latitudes point to a
diversity of land forms on Charon. So far little detail has emerged
about the other moons except more accurate measurements of their
sizes. Retrieving all the data from the brief fly-past of Pluto will
take almost 16 months.


SEDNA IS POSSIBLE EXO-PLANET
CosmosUp

Astronomers at Leiden University suspect that the dwarf planet Sedna,
discovered in 2003, actually originated from another star. With a
diameter of approximately 1000 km, Sedna is a relatively large Kuiper-
belt object -- only Pluto and Eris are larger. Sedna has a very
elongated orbit around the Sun: the point of closest approach to the
Sun is 76 AU (76 times the Earth-Sun distance) but the farthest point
(aphelion) is estimated at 937 AU (31 times Neptune's distance).
Sedna completes an orbit every 11,400 years, making it one of the most
distant objects in the Solar System. Some astronomers think that,
more than 4 billion years ago, a possible encounter with another star
could have led to ice dwarfs being gravitationally captured into
Sedna-like orbits. The passing star would have been 80% as massive as
the Sun and would have passed through the Kuiper Belt and affected the
outer edge of the Solar System. Its passage must have occurred before
the so-called 'late heavy bombardment' which occurred approximately 4
billion years ago. During that interval a large number of asteroids
apparently collided with the early terrestrial planets in the inner
Solar System. The reconstruction of the near-collision suggests that
about 2,000 planetesimals, including Sedna and 2012 VP113, were
captured into our Solar System, and that the passing star would itself
have stolen hundreds of Solar-System ice dwarfs, and hundreds more
would have been lost into interstellar space.


FIVE-STAR DOUBLY ECLIPSING STAR SYSTEM
RAS

Astronomers have discovered for the first time a quintuple star system
containing two eclipsing binary stars. About a third of all stars are
found in pairs or multiple systems. The quintuple system was first
detected in archived data from the SuperWASP (Wide Angle Search for
Planets) project, which uses relatively small and low-cost cameras in
the Canary Islands and South Africa to image almost the whole sky
every few minutes. Over many years, its measurements of the bright-
nesses of individual stars have been assembled into light-curves for
some 30 million sources in the Milky Way. Regular small dips in a
light-curve can reveal the presence of orbiting planets, when they
cross or transit the face of their host star, and SuperWASP has been
extremely successful in finding such 'exo-planets' since it began
operating in 2003. Light-curves also enable eclipsing binary syatems
to be discovered. As seen from the Earth, each star will pass in
front of its companion once in every orbit and eclipse some or all of
its light. That produces a regular pattern of pairs of dips in the
binary's light-curve, whose depths and shapes give indications of the
physical properties of the two stars.

The light-curve of the new quintuple system, designated as 1SWASP
J093010.78+533859.5, initially revealed the presence of a contact
eclipsing binary -- a system in which the two stars are orbiting so
close together that they share an outer atmosphere. Contact binaries
are quite common, but that particular system is notable because its
orbital period is so short, just under six hours. Then it was noted
that the light-curve contained some additional unexpected eclipses,
and the data were re-analysed to reveal a second eclipsing binary at
the same location on the sky. The new binary is detached -- its
component stars are well separated by a distance of about 3 million
km, or about twice the diameter of the Sun -- and it has a longer
orbital period of one and a third days. The two sets of stars are
separated by about 21 (US)-billion km (more than three times Pluto's
distance from the Sun). Spectroscopy then unexpectedly revealed the
presence of a fifth star, up to 2 billion km away from the detached
binary, but not apparently producing any additional eclipses. By
combining the data from the five stars' light-curves and their
spectra, researchers have been able to confirm that they are all
gravitationally bound together in a single system, around 250 light-
years away from us in the constellation of Ursa Major. The data also
let the team determine the stars' masses, sizes and temperatures. All
the stars are rather smaller and cooler than the Sun, but collectively
the system is bright enough (9th magnitude) to be visible in small
telescopes, and amateur astronomers could see the eclipses for
themselves. One particularly interesting finding is that the two
binaries seem to be orbiting in the same plane. That suggests that
they may originally have formed from a single disc of gas and dust,
which broke up as gravity concentrated it into clumps.


MATERIALS TO BUILD EARTH-LIKE PLANETS FOUND IN EVERY PLANETARY SYSTEM
RAS

Earth-like planets orbiting other stars in the Milky Way are three
times more likely to have the same type of minerals as the Earth than
astronomers had previously thought. In fact, conditions for making
the building blocks of Earth-like rocks are ubiquitous throughout the
Milky Way. Minerals made from carbon, oxygen, magnesium and silicon
are thought to control the landscapes of rocky planets that form in
planetary systems around Sun-like stars. A subtle difference in
mineralogy can have a big effect on plate tectonics, heating and
cooling of a planet's surface, all of which can affect whether a
planet is ultimately habitable. Until now, astronomers thought that
rocky planets fell into three distinct groups: those with a set of
building blocks to similar to the Earth's, those that had a much
richer concentration of carbon, and those that had significantly more
silicon than magnesium. The ratio of elements on the Earth has led to
the chemical conditions favourable for life.

Researchers have constructed a simulation of the chemical evolution of
the Milky Way, which results in an accurate recreation of the Milky
Way as we see it today. That has allowed them to examine the
chemistry of processes such as planetary formation in detail. Their
findings came as something of a surprise. At first, they thought that
the model was wrong. As an overall representation of the Milky Way,
everything seemed very good. Everything was in the right place; the
rates of stars forming and stars dying, individual elements and
isotopes all matched observations of what the Milky Way is really
like. But when they looked at planetary formation, every system they
looked at had the same elemental building blocks as the Earth, and not
just one in three. They could not find any fault with the model, so
they went back and checked the observations. They found some
uncertainties that were causing the one-in-three result. When those
were removed, observations agreed with predictions that the same
elemental building blocks are found in every exo-planet system,
wherever it is in the Galaxy. The cloud out of which the Solar System
formed has approximately twice as many atoms of oxygen as carbon, and
roughly five atoms of silicon for every six of magnesium. Observers
trying to ascertain the chemical make-up of planetary systems have
tended to look at large planets orbiting very bright stars, which can
lead to uncertainties of 10 or 20 per cent. In addition, historically
the spectra of oxygen and nickel have been hard to differentiate.
Improvements in spectroscopic techniques have cleaned up the oxygen
spectra, providing data that match the team's estimates. Even with
the right chemical building blocks, not every planet will be just like
the Earth, and conditions allowing for liquid water to exist on the
surface are needed for habitability. We need only to look to Mars and
Venus to see how differently terrestrial planets can evolve. However,
if the building blocks are there, then it is more likely that
Earth-like planets will form -- and three times more likely than had
previously been thought.


PEBBLES POISED TO MAKE PLANETS
RAS

A team of astronomers has announced the discovery of a ring of rocks
circling a very young star. Planets are thought to form from the dust
and gas in discs that encircle young stars. Over time, dust particles
stick together, until they build up bigger clumps. Eventually, the
clumps have enough mass for gravity to become significant, and over
millions of years the clumps crash together to make planets and moons.
In our own Solar System, that process took place about 4500 million
years ago, with the giant planet Jupiter the first to form. Since the
1990s, astronomers have found discs both of gas and dust, and nearly
2000 fully formed planets, but the intermediate stages of formation
are harder to detect. The team used the e-MERLIN array of radio
telescopes that is centred at Jodrell Bank and stretches across
England as an interferometer, mimicking the resolution of a single
large telescope. They observed DG Tauri, a star only 2.5 million
years old and 450 light-years away in the constellation Taurus.
At radio wavelengths, they discovered a faint glow characteristic of
rocks in orbit around the newly formed star. Astronomers knew that
DG Tauri has jets of hot gas flowing off its poles -- a beacon for
stars still in the process of forming -- so they had an idea of what
to look for.

The team was surprised to see also, with only a fraction of the data
it hopes to acquire, a belt of pebbles. The fine detail that could be
seen with the e-MERLIN telescopes was the key to that discovery.
Astronomers could zoom in to a region as small as the orbit of Jupiter
is in the Solar System. They found a belt of pebbles strung along a
very similar orbit -- just where they would be needed if a planet were
to grow in the next few million years. The e-MERLIN observations were
made at a wavelength of 4.6 cm. To give off such radio waves, rocky
chunks at least a centimetre in size are needed, and the shape of the
belt confirms the rocks as the source of the radio waves. By imaging
the rocky belts of many stars, the team will look for clues as to how
often planets form, and where, around stars that will evolve into
objects like the Sun. The ultimate aim is to zoom in and see
'extra-solar Earths' being born, five times closer in to their host
stars than Jupiter's orbit. Upgrades to e-MERLIN's capabilities in
the next few years, as well as the construction of the new Square-
Kilometre Array (with its HQ at Jodrell Bank), make that a real
possibility.


HOW NEUTRON STAR KICKS CAN BREAK UP CLUSTERS
RAS

A supernova explosion at the end of a large star's life can leave the
collapsed core, or neutron star, hurtling away from its dust and gas
envelope at hundreds of kilometres per second. Now, astronomers have
found that even a tiny number of such neutron-star 'natal kicks' can
have a dramatic effect on the lifetime of surrounding star clusters.
The fast-moving neutron stars can cause star clusters to lose mass and
break apart up to four times more quickly. Astronomers have known for
some time that there are two distinct scenarios for the break-up of
star clusters: a smooth, gradual loss and a sudden discarding of mass.
It is analogous to the difference between skiing down a gentle slope
and jumping off a cliff. Because the dividing line between the two
modes is very sharp, it is not surprising that a small effect can make
a big difference. The study suggests that natal kicks from neutron
stars could be one of the triggers that sends star clusters into
'jumping' modes of rapid dissolution rather than the more gradual
'skiing' one. While neutron-star natal kicks are known to occur,
their frequency, distribution and cause are still uncertain. The high
velocities from the kicks should send neutron stars beyond the
gravitational control of the star clusters in which they are born.
However, because the neutron stars are very hard to observe, their
retention fraction in globular clusters is still unknown. The team
ran a series of computer simulations of the evolution of clusters of
different sizes, either with or without neutron-star natal kicks.
They found that even though neutron stars accounted for less than 2
per cent of the star cluster by mass, the presence of kicks could have
a big effect on the cluster's evolution. In particular, the presence
of kicks and the 'jumping' mode of rapid mass loss meant that the
clusters never achieved the high degree of central concentration of
stars, observed in about 20 per cent of clusters, which is often
considered to be an outcome of the process of 'core collapse'. On the
other hand, all longer-lived ('skiing') models showed signatures of
core collapse, a phenomenon resulting from the slow dynamical
evolution of a stellar system, driven by gravitational encounters
between individual stars. It seems that apparently minor differences
can have very large effects.


LUMINOUS RED NOVA OUTBURST IS COLLIDING RED GIANT
RAS

Observations of a rare astronomical phenomenon, called a luminous red
nova, suggest that the bright outburst was caused by a red giant
colliding with another star. Astronomers used the Liverpool Telescope
to track a nova outburst over several months and hunted through the
Hubble telescope archive to identify possible progenitors. The
outburst was first observed in 2015 January in the Andromeda galaxy
(M31) by the Global MASTER Robotic Network, a Russian-led network of
telescopes dedicated to looking for transient objects in the night
sky. Initially, astronomers thought it was a classical nova, but,
watching the way its brightness evolved at different wavelengths, they
soon realised that the object was unusual and was a luminous red nova.
Classical novae are not particularly rare, with around 30 observed
each year in M31 alone. They are thought to occur in binary systems
when material falls onto the surface of a white dwarf from its larger
companion star, causing a relatively short burst of nuclear fusion.
By comparison, very few luminous red novae have been found to date.
Their cause is still uncertain, but they may be the result of two
stars merging together, causing a very sudden and dramatic brightening
of the system.

The Liverpool team first observed the new system, dubbed M31LRN 2015,
three days after its discovery. The outburst brightened over several
days. After reaching a peak, the nova faded quickly at blue
wavelengths, but remained bright at the redder wavelengths for several
weeks. Spectral analysis showed an initial burst of hydrogen
emission, and as it faded, features resembling those of a cool red
star emerged. The outburst was observed again in May, and had all but
disappeared in the optical, but was still bright in the infrared.
The team searched the Hubble archives for objects at the same place.
An image taken in 2004 showed the likely progenitor star: a red giant.
Interestingly, the system appears to have shown evidence of hydrogen
emission many years before the outburst, although the source of the
emission is not clear. The team found that M31LRN 2015 showed strong
similarities to other objects classified as luminous red novae. If a
single mechanism is responsible for all such events, the evidence
suggests merging stars as the cause.


BEST CANDIDATE SUPERNOVA?
RAS

Using the robotic Liverpool Telescope, an international team of
scientists has found what looks like the best pre-explosion candidate
yet for a type-1a supernova, where a massive and extremely dense
star in the Andromeda galaxy is dragging material away from its
companion. The star is destined to be completely destroyed in the
(astronomically) near future in a catastrophic explosion. Our Sun is
expected to have a relatively gentle end to its life, but some stars
have a more violent demise in prospect -- they are destined to explode
as supernovae, briefly shining as brightly as a whole galaxy of stars.
One class of such explosions, type-1a supernovae (SN1a), is
fundamental to our understanding of the evolution of the Universe.

Some binary systems of stars are particularly close together. Where
one of the stars is a white dwarf (the long-extinguished super-dense
remnant of a star that was once similar to the Sun), and the other is
a more normal companion, the gravity of the white dwarf fundamentally
changes both objects. The outer atmosphere of the normal star, mostly
hydrogen and helium, flows towards the white dwarf, forming a highly
compressed layer on its surface. Under the right conditions, that
material will heat up enough for runaway nuclear fusion to take place,
similar to that in a hydrogen bomb, but far more powerful than
anything possible on Earth. The explosion is a nova (meaning 'new
star'), and for a short period the system will have the brightness of
between 100 and 500 thousand Suns. Some, but by no means all, of the
accumulated material from the companion star will be ejected into
space.

Of the 400 novae that have been seen in our Galaxy, a few have been
seen to erupt more than once. Those 'recurrent novae' erupt
frequently, as the mass of the white dwarf is already high from the
millions of years of transfer of material and its companion star is
losing material at a high rate. In the Milky Way, the most active
recurrent nova is U Scorpii, which erupts about once a decade. But
the cycle of explosions cannot go on for ever. Once a white dwarf
accumulates close to 1.4 times the mass of the Sun, the 'critical
mass', its core temperature will have risen to around 500 million
degrees (30 times hotter than the centre of the Sun). The stellar
material subsequently undergoes another and much more powerful
thermonuclear reaction, in an enormous explosion that destroys the
white dwarf in a few seconds, releasing vast amounts of energy in the
process. That is a type-1a supernova, and for a number of days it has
the brightness of billions of Suns.

In 2008 scientists observed the eruption of a star, later confirmed to
be a nova, in the Andromeda galaxy (M31), the nearest large galaxy to
our own, some 2.5 million light-years away. Remarkably the same star,
catalogued as M31N 2008-12a, erupted again in 2009, 2011, 2012, 2013
and 2014. The team initiated a follow-up programme in 2013 and 2014,
using the Liverpool Telescope and X-ray observations from the orbiting
Swift observatory. Their work shows that in astronomical terms, M31N
2008-12a is on the brink of catastrophe. With explosions in rapid
succession, the white dwarf must be just a fraction under the critical
mass and could be torn to pieces in a supernova any time in the next
few hundred thousand years. The system is right on the cusp of total
destruction, so we are getting a first look at how it is changing
right before it erupts as a supernova. That could happen tomorrow, or
hundreds of thousands of years in the future. The international team
hopes to continue to monitor M31N 2008-12a for the foreseeable future.
Type-1a supernovae are all thought to have similar brightnesses, so
they are used as 'standard candles' to gauge the distances to galaxies
and measure the properties of the Universe as a whole. Understanding
systems like M31N 2008-12a is a key part of that.


FAR FEWER GALAXIES THAN MIGHT BE EXPECTED
Michigan State University

Over the years, the Hubble space telescope has allowed astronomers to
look deep into the Universe. The long view stirred theories of untold
thousands of distant, faint galaxies. New research, however, offers a
theory that reduces the estimated number of the most distant galaxies
by 10 to 100 times. Earlier estimates placed the number of faint
galaxies in the early Universe to be hundreds or thousands of times
larger than the few bright galaxies that we can actually see with
Hubble. Astronomers now think that the number could be closer to only
ten times larger. The team ran computer simulations to examine the
formation of galaxies in the early Universe. The team simulated
thousands of galaxies at a time, including the galaxies' interactions
through gravity or radiation. The simulated galaxies were consistent
with observed distant galaxies at the bright end of the distribution
-- in other words, those that have been discovered and whose existence
is confirmed. The simulations did not, however, show an exponentially
growing number of faint galaxies, as had previously been predicted.
The number of those at the lower end of the brightness distribution
was flat rather than increasing sharply. The simulations will be
tested further when the much-anticipated James Webb space telescope
comes into operation in late 2018. The improved technology will
afford astronomers even-more-detailed views of space than those that
Hubble has produced in recent years. The Hubble telescope can see
just the 'tip of the iceberg' of the most-distant galaxies. While the
Webb telescope will improve views of distant galaxies, it has a
relatively small field of view. As a result, the observations must
take into account cosmic variability -- the statistical variation in
the number of galaxies from place to place.


HIDDEN SUPER-MASSIVE BLACK HOLES REVEALED
RAS

Astronomers have found evidence for a large population of hidden
super-massive black holes in the Universe. Using NASA's Nuclear
Spectroscopic Telescope Array (NuSTAR) satellite observatory,
scientists detected the high-energy X-rays from five super-massive
black holes that are shielded from direct view by dust and gas.
The research, led by astronomers at Durham, supports the theory that
millions more super-massive black holes potentially exist, but are
hidden from view. The scientists pointed NuSTAR at nine candidate
hidden super-massive black holes that were thought to be extremely
active at the centres of galaxies, but where the full extent of such
activity was potentially obscured from view. High-energy X-rays found
from five of the galaxies confirmed that they possessed holes hidden
by dust and gas. The five were much brighter and more active than
previously thought, as they rapidly captured surrounding material and
emitted large amounts of radiation. Such observations were not
possible before NuSTAR, which was launched in 2012 and is able to
detect X-rays of much higher energy than previous satellites.
High-energy X-rays are more penetrating than low-energy ones, so we
can see deeper into the gas surrounding the black holes. NuSTAR
allows us to see how big the hidden objects are, and is helping us to
learn why only some black holes appear obscured.


RINGS AND LOOPS IN THE STARS
RAS

A ring of dust 200 light-years across, and a loop covering a third of
the sky, are among the results in a new map from the Planck satellite.
Planck, launched in 2009 to study the ancient light of the Big Bang,
has also made maps of our Galaxy in microwaves (cm to mm wavelengths).
Microwaves are generated by electrons spiralling in the Galaxy's
magnetic field at nearly the speed of light (the synchrotron process),
by collisions in interstellar plasma, by thermal vibration of inter-
stellar dust grains, and by 'anomalous' microwave emission (AME),
which may be from spinning dust grains. The relative strengths of
those processes change with wavelength, and can separated by the use
of multi-wavelength measurements from Planck, from the WMAP satellite,
and from ground-based radio telescopes, giving maps of each component.
The new maps show regions covering huge areas of our sky that produce
AME; that process, discovered only in 1997, could account for a large
amount of Galactic microwave emission with a wavelength near 1 cm.
One place where it is particularly bright is the 200-light-year-wide
dust ring around the Lambda Orionis nebula (the 'head' of Orion).
This is the first time that the ring has been seen in such a way. A
wide-field map also shows synchrotron loops and spurs (where charged
particles spiral around magnetic fields), including the huge Loop 1,
discovered more than 50 years ago. Remarkably, astronomers are still
very uncertain about its distance -- it could be anywhere between 400
and 25,000 light-years away -- and though it covers about a third of
the sky it is impossible to say exactly how big it is.


NEW SURVEY TO SHINE LIGHT ON DARK MATTER
ESO

Around 85% of the matter in the Universe is dark, and of a type not
understood by physicists. Although it does not shine or absorb light,
astronomers can detect dark matter through its effect on stars and
galaxies, specifically from its gravitational pull. A major project
with powerful survey telescopes is now showing more clearly than
before the relationships between dark matter and the shining galaxies
that we can observe directly. The project, known as the Kilo-Degree
Survey (KiDS), uses imaging from the VLT Survey Telescope (VST) at
Paranal and its huge camera,OmegaCAM. Sited at the Paranal Observa-
tory in Chile, that telescope is dedicated to surveying the night sky
in visible light, and it is complemented by the infrared survey
telescope VISTA. The survey may allow astronomers to make measure-
ments of dark matter, the structure of galaxy haloes, and evolution of
galaxies and clusters. The first KiDS results show to some extent how
the characteristics of the observed galaxies are determined by the
vast invisible clumps of dark matter surrounding them. One of the
major goals of the VST is to map out dark matter and to use the maps
to understand the mysterious 'dark energy' that is said to be causing
the Universe's expansion to accelerate.

The best way to work out where the dark matter lies is through
gravitational lensing -- the distortion of the Universe's fabric by
gravity, which deflects the light coming from distant galaxies far
beyond the dark matter. By studying that effect it is possible to map
out the places where gravity is strongest, and hence where the matter,
including dark matter, resides. The KiDS team has used that approach
to analyse images of over two million galaxies, typically 5.5 billion
light-years away. It has studied the distortion of light emitted from
the galaxies, which is deflected as it passes massive clumps of dark
matter during its journey. The first results come from only 7% of the
final survey area and concentrate on mapping the distribution of dark
matter in clusters of galaxies. Most galaxies live in clusters,
including our own Milky Way, which is part of the 'Local Group', and
understanding how much dark matter they contain is a test of the whole
theory of how galaxies form in the cosmic web. From the gravitational
lensing effect, the groups turn out to contain around 30 times more
dark than visible matter. Interestingly, the brightest galaxy nearly
always sits in the middle of the dark-matter clump. That feature of
galaxy formation, in which galaxies are sucked into groups and pile up
in the centre, has never been demonstrated so clearly before. The
findings are just the start of a major programme to exploit the data
coming from the survey telescopes.


Bulletin compiled by Clive Down

(c) 2015 the Society for Popular Astronomy

The Society for Popular Astronomy has been helping beginners to
amateur astronomy -- and more experienced observers -- for more than
60 years. If you are not a member then you may be missing something.
Membership rates are extremely reasonable, starting at just £20 a year
in the UK. You will receive our bright bi-monthly magazine Popular
Astronomy, help and advice in pursuing your hobby, the chance to hear
top astronomers at our regular meetings, and other benefits. The best
news is that you can join online right now with a credit card or debit
card at our lively website: www.popastro.com


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