SUN'S MAGNETIC CAGE STOPPED SOLAR ERUPTION
NASA/Goddard Space Flight Center
New research using NASA data shows that a dramatic magnetic power struggle
at the Sun's surface lies at the heart of solar eruptions. The work high-
lights the role of the Sun's magnetic landscape, or topology, in the dev-
elopment of solar eruptions that can trigger 'space weather' events around
the Earth. The scientists examined solar flares, which are intense bursts
of radiation and light. Many strong solar flares are followed by a coronal
mass ejection, or CME, a massive, bubble-shaped eruption of solar material
and magnetic field, but some are not -- what differentiates the two
situations is not clearly understood. Using data from NASA's Solar Dynamics
Observatory, or SDO, the scientists examined a 2014 October Jupiter-sized
sunspot group, an area of complex magnetic fields, often the site of solar
activity. That was the biggest group in the past two solar cycles and a
highly active region. Though conditions seemed ripe for an eruption, the
region never produced a major CME on its journey across the Sun. It did,
however, emit a powerful X-class flare, the most intense class of flares.
What determines, the scientists wondered, whether a flare is associated
with a CME?
The team of scientists included SDO's observations of magnetic fields at the
Sun's surface in powerful models that calculated the magnetic field of the
Sun's corona, or upper atmosphere, and examined how it evolved in the time
just before the flare. The model reveals a battle between two key magnetic
structures: a twisted magnetic rope -- known to be associated with the onset
of CMEs -- and a dense cage of magnetic fields overlying the rope. The
scientists found that that magnetic cage physically prevented a CME from
erupting that day. Just hours before the flare, the sunspot's natural
rotation contorted the magnetic rope and it grew increasingly twisted and
unstable, like a tightly coiled rubber band, but the rope never erupted from
the surface: the model demonstrated that it did not have enough energy to
break through the cage. It was, however, volatile enough to lash through
part of the cage, triggering the strong solar flare. By changing the
conditions of the cage in their model, the scientists found that if the
cage had been weaker that day, a major CME would have erupted. The group is
interested in developing its model further to study how the conflict between
the magnetic cage and rope plays out in other eruptions.
OPPORTUNITY ROVER HAS SPENT OVER 5000 DAYS ON MARS
NASA
The Sun has risen on NASA's solar-powered Mars rover Opportunity over 5,000
times, sending rays of energy to a golf-cart-size robotic field geologist
that continues to provide revelations about the Red Planet. A Martian 'sol'
lasts about 40 minutes longer than an Earth day, and a Martian year lasts
nearly two Earth years. Opportunity's Sol 1 was landing day, 2004 Jan. 25.
The prime mission was planned to last 90 sols; NASA did not expect the rover
to survive through a Martian winter, but Opportunity has worked actively
right through the lowest-energy months of its eighth Martian winter. From
the rover's perspective on the inside slope of the western rim of Endeavour
Crater, the milestone sunrise appeared over the basin's eastern rim, about
22 kilometres away. Opportunity has driven over 45 kilometres from its
landing site to its current location about one-third of the way down
'Perseverance Valley', a shallow channel incised from the rim's crest to the
crater's floor. The rover has returned about 225,000 images, all promptly
made public online. The mission made headlines during its first months with
the evidence about ground-water and surface-water environments on ancient
Mars. Opportunity trekked to increasingly larger craters to look deeper
into Mars and further back into Martian history, reaching Endeavour Crater
in 2011. Researchers are now using the rover to investigate the processes
that shaped Perseverance Valley.
DUSTY GAS TORUS AROUND MASSIVE BLACK HOLE
National Institutes of Natural Sciences
Almost all galaxies conceal monstrous black holes in their centres. Re-
searchers have known for quite a long time that the more massive a galaxy
is, the more massive its central black hole tends to be. That sounds
reasonable at first, but host galaxies are 10 billion times more massive
than the central black holes; it would seem difficult for two objects of
such vastly different scales directly to affect one another. So how could
such a relationship develop? Aiming to solve that shadowy problem, a team
of astronomers utilized ALMA to observe the centre of the spiral galaxy M77.
The central region of M77 is an 'active galactic nucleus', or AGN, which
means that matter is vigorously falling toward the central super-massive
black hole and emitting intense light. AGNs can strongly affect the
surrounding environment, so they are important objects for solving the
problem of the co-evolution of galaxies and black holes. The team imaged
the area around the supermassive black hole in M77 and resolved a compact
gaseous structure with a radius of 20 light-years. They found that the
compact structure is rotating around the black hole, as expected. Many
astronomers have observed the centre of M77 before, but the rotation of
the gas around the black hole has never been seen so clearly. Besides the
superior resolution of ALMA, the selection of molecular emission lines to
observe was a key to revealing the structure. The team observed specific
microwave emission from hydrogen cyanide molecules (HCN) and formyl ions
(HCO+). Those molecules emit microwaves only in dense gas, whereas the more
frequently observed carbon monoxide (CO) emits microwaves under a variety of
conditions. The torus around the AGN is assumed to be very dense, and the
team's strategy was right on the mark.
Interestingly, the distribution of gas around the supermassive black hole
is much more complicated than what a simple unified model suggests. The
torus seems to have an asymmetry and the rotation is not just following the
gravity of the black hole but also contains highly random motion. Those
facts could indicate that the AGN had a violent history, possibly including
a merger with a small galaxy. Nevertheless, the identification of the
rotating torus is an important step. The Milky Way galaxy, where we live,
also has a supermassive black hole at its centre. That black hole is,
however, in a very quiet state; only a tiny amount of gas is accreting onto
it. To investigate AGNs in detail, astronomers need to observe the centres
of distant galaxies. M77 is one of the nearest AGN and its very centre can
be observed in some detail.
ANDROMEDA GALAXY SAME SIZE AS MILKY WAY
RAS
A new technique for measuring the masses of galaxies has been applied to our
closest galactic neighbour -- and it has found that the Andromeda galaxy is
roughly the same size as the Milky Way, and not two to three times bigger as
was previously thought. That means that, when the two galaxies merge in
about 4 billion years' time, the Milky Way won't be fully consumed by the
Andromeda galaxy as previous models suggested. The team found that the mass
of the Andromeda galaxy is around 800 billion solar masses. It is hard to
measure the physical dimensions of our own Galaxy from the inside, but
astronomers have been able to calculate its mass -- around 800 to 1200
billion solar masses. That finding puts the two galaxies, separated by a
distance of about 2.5 million light-years, about on a par in terms of size.
Our galaxy and Andromeda are the two largest ones in what is known as the
Local Group, a collection of more than 30 galaxies that spans roughly 10
million light-years. The new measurement was obtained by a technique that
calculates the speed required to escape the gravitational pull of a galaxy,
or escape velocity. The team used the movement of high-velocity planetary
nebulae within the Andromeda galaxy to calculate that galaxy's escape
velocity, and found it to be around 470 +/- 40 kilometres per second.
A similar technique was used in 2014 to determine the mass of the Milky
Way. It was also found that the Milky Way contained less dark matter than
previously thought -- a result which has also been found for Andromeda by
the new research. The result means that we may need new simulations to see
what might happen when the two galaxies inevitably merge. But it also
means that we have a new way of collecting data about our Universe.
RARE FIRST LIGHT FROM MASSIVE SUPERNOVA
University of California - Berkeley
On 2016 Sept. 20, Victor Buso, an amateur astronomer in Argentina, was
testing a new camera on his 16-inch telescope by taking a series of short-
exposure photographs of the spiral galaxy NGC 613, which is about 80 million
light-years away in the southern constellation Sculptor. Luckily, he
examined the images immediately, and noticed, near the end of a spiral arm,
a faint point of light quickly brightening that was not visible in his first
set of images. A team of astronomers at the Instituto de Astrofisica de La
Plata in Argentina soon learned of the serendipitous discovery and realized
that Buso had caught a rare event, part of the first hour after light
emerges from a massive exploding star. The team estimated Buso's chances of
such a discovery, his first supernova, at one in 10 million or even less.
An international group of astronomers was asked to help conduct additional
frequent observations of the supernova, called SN 2016gkg, over the next two
months, revealing more about the type of star that exploded and the nature
of the explosion. Scientists obtained a series of seven spectra with the
Shane 3-m telescope at the Lick Observatory, and with the twin 10-m tele-
scopes of the Keck Observatory in Hawaii. They allowed the international
team to determine that the explosion was a Type IIb supernova: the explosion
of a massive star that had previously lost most of its hydrogen envelope, a
species of exploding star first identified observationally in 1987.
Combining the data with theoretical models, the team estimated that the
initial mass of the star was about 20 times the mass of the Sun, though it
had lost most of its mass, probably to a companion star, and was down to
about 5 solar masses before exploding. The team continued to monitor the
supernova's changing brightness for two months with other Lick telescopes
-- the 0.76-m Katzman Automatic Imaging Telescope and the 1-m Nickel
telescope.
MOST DISTANT SUPERNOVA EVER DETECTED
University of Southampton
An international team of astronomers has confirmed the discovery of the most
distant supernova ever detected -- an explosion that took place 10.5
billion years ago, or three-quarters the age of the Universe itself. The
exploding star, named DES16C2nm, was detected by the Dark Energy Survey
(DES), an international collaboration to map several hundred million
galaxies in order to find out more about dark energy -- the unidentified
force that is believed to be causing the accelerated expansion of the Uni-
verse. A supernova is the explosion of a massive star at the end of its
life cycle. DES16C2nm is classified as a superluminous supernova (SLSN),
the brightest and rarest class of supernovae, first discovered ten years
ago, thought to be caused by material falling onto the densest object in the
Universe -- a rapidly rotating neutron star newly formed in the explosion of
a massive star. The ultraviolet light from SLSN informs astronomers of the
amount of metal produced in the explosion and the temperature of the
explosion itself, both of which are keys to understanding what causes and
drives those cosmic explosions. Finding more distant events, to determine
the variety and sheer number of those events, is the next step.
DES16C2nm was first detected in 2016 August, and its distance and extreme
brightness were confirmed in October that year using three of the world's
most powerful telescopes -- the Very Large Telescope and the Magellan, in
Chile, and the Keck Observatory, in Hawaii. More than 400 scientists from
over 25 institutions worldwide are involved in the DES, a five-year project
which began in 2013. The collaboration built and is using an extremely
sensitive 570-megapixel digital camera, DECam, mounted on the Blanco 4-m
telescope at Cerro Tololo Inter-American Observatory, high in the Chilean
Andes, to carry out the project. Over five years (2013-2018), the DES
collaboration is using 525 nights of observation to carry out a deep,
wide-area survey to record information from 300 million distant galaxies.
The survey is imaging 5,000 square degrees of the southern sky in five
optical filters to obtain detailed information about each galaxy.
A fraction of the survey time is used to observe smaller patches of sky
roughly once a week to discover and study thousands of supernovae and other
astrophysical transients.
NOCTURNAL ANIMALS NAVIGATE BY THE STARS
Lund University:
Nocturnal animals can use the stars and the Milky Way to find their way
during the darkest hours. There are advantages to being active in the
night. Fewer parasites are active, and the same goes for predators.
Moreover, there are not as many competitors for food as there are during
the day. For animals that migrate or search for food over vast distances in
particular, the cooler hours of the night are preferable to the heat of the
day. A key requirement for nocturnal animals is that they can hold their
course in the dark. Migrating birds that take off at sunset rely on their
magnetic compass, but also the star compass when they use individual stars
for orientation. Dung beetles do not use individual stars. Instead they
travel through the night with the help of the light from the Milky Way,
which contrasts with the surrounding dark sky. Studies also support that
seals, moths, frogs and other animals use the starry sky to navigate at
night. Animals with camera eyes, the type of eyes that we humans possess,
can discern individual stars. Insects with compound eyes most likely can
not, but scientists believe that they can interpret the starry sky and the
Milky Way as patterns of light. We still know very little about how
nocturnal animals experience and interpret the night sky. For example, no
one has yet determined whether, and how, migrating birds change their point
of reference in the night sky when they pass the equator. Emerging
technologies, such as highly-sensitive cameras, may allow us to discover
many more species that also use the starry skies to guide them during the
darkest hours of the night.
Topic: Early March Astronomy Bulletin (Read 1423 times)