NEW CLUES TO THE SOLAR CYCLE
NASA
It is well known that the Sun has cycles of activity, manifested by
sunspots and flares, with a period of about 11 years. However, the
timing of the solar cycle is far from precise. Since records began in
the 17th century, the intervals between successive solar maxima have
varied between 9 and 14 years. Now, researchers have discovered a
marker to track the course of the solar cycle -- little bright spots
in the solar atmosphere that allow us to observe the constant roiling
of material inside the Sun. The markers provide a way to watch
magnetic fields evolve and move through the Sun. Historically,
theories about the solar cycle relied on sunspots, but because
sunspots are areas of intense magnetic fields, magnetic measurements
are also relevant to theories.
The processes that make sunspots are not well understood. The bright
points now recognized in the solar atmosphere act like buoys anchored
to processes occurring deeper down. Over the course of a solar cycle,
the sunspots tend to migrate to progressively lower latitudes. The
prevailing theory is that two symmetrical, grand loops of material,
one in each solar hemisphere, like huge conveyor belts, sweep from the
poles to the equator where they sink deeper down into the Sun and then
make their way steadily back to the poles. The conveyor belts also
move the magnetic field through the churning solar atmosphere. The
theory suggests that sunspots move with that flow -- tracking sunspots
has allowed a study of the flow, and theories about the solar cycle
have developed on the basis of that progression. But why do the
sunspots appear only at latitudes lower than about 30 degrees?
What causes the sunspots of consecutive cycles to reverse their magnetic
polarities? Why is the timing of the cycle so variable?
In 2010, scientists began tracking the sizes of areas where there are
as many magnetic fields pointing down into the Sun as pointing out.
They found magnetic parcels in sizes that had been seen before,
but also observed much larger parcels than those previously noted --
about the diameter of Jupiter. They also noticed that ubiquitous
spots of extreme ultraviolet and X-ray light, known as brightpoints,
prefer to hover around the vertices of those large areas, dubbed
'g-nodes' because of their giant scale. The brightpoints and g-nodes,
therefore, offer a new way to track how material flows inside the Sun.
Researchers then collected information about the movement of those
features over the past 18 years of available observations from the
SOHO satellite records, to monitor how the last solar cycle progressed
and the current one started. They found that bands of those markers
-- and therefore the corresponding magnetic fields below -- also moved
steadily toward the equator, along the same path as sunspots, but
beginning at latitudes of about 55 degrees. In addition, each
hemisphere of the Sun usually had more than one of the bands present.
The observations suggest that the Sun is populated with bands of
differently polarized magnetic material that, once formed, steadily
move toward the equator from high latitudes. The polarities of the
bands alternate in each hemisphere such that the polarities always
cancel. For example, in the Sun's northern hemisphere, the band
closest to the equator -- perhaps of northern polarity -- would have
magnetic field lines that connect it to another band, at higher
latitudes, of southern polarity. In the southern hemisphere the bands
would be almost mirror images of the northern ones, with southern
polarity near the equator and northern at higher latitudes. Magnetic
field lines would connect the four bands, within each hemisphere and
across the equator as well. Solar minimum occurs when the field lines
are relatively short and the Sun's magnetic system is relatively calm,
producing few sunspots and eruptions. When the two low-latitude bands
reach the equator their polarities cancel each other out and they
disappear. The process, from migratory start to equatorial finish,
takes 19 years on average. After the equatorial cancellation, the Sun
is left with just two large bands that have migrated to about 30
degrees latitude. The magnetic field lines from those bands are much
longer and so the bands in each hemisphere feel less of each other.
At that point the sunspots begin to grow rapidly on the bands,
beginning the ramp-up to solar maximum; the process of generating a
new band of opposite polarity has, however, already begun at high
latitudes. When that new band begins to appear, the complex four-band
connection starts again and the number of sunspots in the low-latitude
bands starts to decrease. In that model, it is the magnetic band's
cycle -- the lifetime of each band as it moves toward the equator --
that truly defines the solar cycle. Thus, the 11-year cycle can be
viewed as the overlap between two much longer cycles. The new
conceptual model also provides an explanation of why sunspots are
trapped below 30 degrees and abruptly change sign. However, the model
creates a question about a different latitude line: why do the
magnetic markers, the brightpoints and g-nodes, start appearing at 55
degrees? Above that latitude, the solar atmosphere appears to be
disconnected from the rotation beneath it, so there is reason to
believe that, inside the Sun, there is a very different internal
motion and evolution at high latitudes compared to the region near the
equator.
ROSETTA COMET IS DARKER THAN CHARCOAL
NASA
An instrument on the Rosetta orbiter has returned its first data from
comet Churyumov-Gerasimenko. The instrument, named Alice, began
mapping the comet's surface last month, recording the first far-
ultraviolet spectra of the surface. The comet is unusually dark --
darker than charcoal-black -- at ultraviolet wavelengths. Alice also
detected both hydrogen and oxygen in the comet's coma, or atmosphere.
Rosetta scientists also discovered that the surface so far shows no
large water-ice patches. They expected to see ice patches on the
surface because the comet is still too far away for the Sun's warmth
to turn its water into vapour. Alice is said to have more than 1000
times the data-gathering capability of instruments flown a generation
ago, yet it weighs less than 4 kg and draws just four watts of power.
MILKY WAY RESIDES IN NEWLY IDENTIFIED SUPERCLUSTER
National Radio Astronomy Observatory
Astronomers using the Green Bank Telescope (GBT) -- among other
telescopes -- have determined that our own Milky Way galaxy is part of
a newly identified supercluster of galaxies, which they have dubbed
'Laniakea', which means 'immense heaven' in Hawaiian. The discovery
clarifies the boundaries of our galactic neighbourhood and establishes
previously unrecognized linkages among various galaxy clusters.
Superclusters are among the largest structures in the Universe. They
are made up of groups, like our own Local Group, that contain dozens
of galaxies, and massive clusters that contain hundreds of galaxies,
all interconnected in a web of filaments. Though the structures are
interconnected, they have poorly defined boundaries.
By using the GBT and other radio telescopes to map the velocities of
galaxies throughout the 'local' Universe, the team was able to define
the region of space where each supercluster dominates. The Milky Way
is in the outskirts of one such supercluster, whose extent has been
mapped by that method. That so-called Laniakea Supercluster is 500
million light-years in diameter and contains a total mass of 10 to the
power 17 Suns spread across 100,000 galaxies. The study also
clarifies the role of the Great Attractor, a gravitational focal point
in intergalactic space that influences the motion of our Local Group
of galaxies and other galaxy clusters. Within the boundaries of the
Laniakea Supercluster, galaxy motions are directed inward, in the same
way as streams of water follow descending paths toward a valley. The
Great Attractor region is a flat-bottomed gravitational valley with a
sphere of attraction that extends across the Laniakea Supercluster.
MILKY WAY'S MISSING SATELLITE GALAXIES
RAS
Scientists believe that they have found a way to explain why there are
fewer galaxies orbiting the Milky Way than they expected. Computer
simulations of the formation of our Galaxy suggest that there should
be many more small galaxies around the Milky Way than are observed.
That has thrown doubt on the generally accepted theory of cold dark
matter, an invisible and mysterious substance that scientists predict
should allow for more galaxy formation around the Milky Way than is
seen. Now researchers at the Institute for Computational Cosmology
and the Institute for Particle Physics Phenomenology at Durham
University think they have found a potential solution to the problem.
They suggest that dark-matter particles, as well as feeling the force
of gravity, could have interacted with photons and neutrinos in the
young Universe, causing the dark matter to scatter. They think that
clumps or haloes of dark matter that emerged from the early Universe
trapped the intergalactic gas needed to form stars and galaxies.
Scattering the dark-matter particles wipes out the structures that can
trap gas, stopping more galaxies from forming around the Milky Way and
reducing the number that should exist. Scientists do not know how
strong such interactions might be, so that is where the simulations
come in. By tuning the strength of the scattering of particles, the
prospective number of small galaxies is changed, which might throw
light on the physics of dark matter and how it might interact with
other particles in the Universe.
There are several theories about why there are not more galaxies
orbiting the Milky Way, which include the idea that heat from the
first stars sterilised the gas needed to form stars. The researchers
say that their current findings offer an alternative theory and could
provide a novel technique to probe interactions between other
particles and cold dark matter. Some astronomers think that most of
the matter in the Universe consists of the elementary particles known
as dark matter. Their model can be made to explain how most of the
Universe looks, except in our own vicinity, where it fails miserably.
The model predicts that there should be many more small satellite
galaxies around our Milky Way than we can observe. However, by using
computer simulations to allow the dark matter to become a little more
interactive with the rest of the material in the Universe, such as
photons, the theory can be made to match more nearly the number of
galaxies around us.
WHY SPIRAL GALAXIES ARE SO COMMON
ESO
Computer simulations from the 1970s predicted that mergers between two
comparable disc galaxies would result in an elliptical galaxy. But
now researchers using ALMA and other radio telescopes have found
evidence that merging galaxies can instead form disc galaxies, and
that that outcome is in fact quite common. That could explain why
there are so many spiral galaxies like the Milky Way. To identify the
final shapes of galaxies after mergers observationally, the group
studied the distribution of gas in 37 galaxies that are in their final
stages of merging. ALMA and several other radio telescopes were used
to observe emission from carbon monoxide, an indicator of molecular
gas. The study found that most of the mergers show pancake-shaped
areas of molecular gas, and hence are disc galaxies in the making.
There is, however, a lot more to discover, and astronomers have to
start focusing on the formation of stars in the gas discs. Further-
more, they need to look further out into the more distant Universe.
INDIA'S MARS ORBITER MISSION
ISRO
India's ambitious Mars Orbiter Mission (MOM), scheduled to enter Mars
orbit later this month, is said to be 'in the pink of health'. The
spacecraft has completed 95% of its journey to Mars and is less than
four million km away from it. Scientists said that they would
undertake a "challenging task" on September 24 when they would restart
the liquid-propellent engine, which has been in sleep mode for nearly
ten months, for a critical manoeuvre of the spacecraft. The project,
named Mangalyaan, was launched by the 'Polar Satellite Launch Vehicle'
on November 5 last year.
COMMERCIAL COMPANIES WILL TRANSPORT ASTRONAUTS TO ISS
NASA
It is hoped that in a few years American astronauts will once again
travel to and from the International Space Station in American
spacecraft. The space agency has reported its selection of Boeing and
SpaceX to transport U.S. crews to and from the station in their
CST-100 and Crew Dragon spacecraft, respectively, with a goal of
ending America's complete reliance on Russia in 2017. The 'Commercial
Crew Transport Capability' (CCtCap) contracts are designed to complete
the NASA certification for transport systems capable of carrying
people into orbit. Once certification is complete, NASA plans to use
those systems to ferry astronauts to and from the International Space
Station. Turning over low-Earth-orbital transport to private industry
will also allow NASA to focus on a more ambitious mission -- sending
people to Mars.
Topic: Late September Astronomy Bulletin (Read 1829 times)