COSMIC RAYS INTENSIFY
Spaceweather.com
Researchers have long known that solar activity and cosmic rays have
an inverse relationship. As solar activity declines, cosmic rays
intensify. Lately, solar activity has been very low indeed. Are
cosmic rays responding? The answer is 'yes'. Researchers have been
using helium balloons to monitor cosmic rays in the stratosphere over
California. Their latest data show an increase of almost 13% since
2015. Cosmic rays, which are accelerated towards the Earth by distant
supernova explosions and other violent events, are a form of space
weather. They can seed clouds, trigger lightning, and penetrate
commercial aeroplanes. Furthermore, there are studies linking cosmic
rays with cardiac arrhythmias and sudden cardiac death in the general
population. The main reason cosmic rays intensifying is the Sun.
Solar storm clouds such as coronal mass ejections (CMEs) sweep aside
cosmic rays when they pass by the Earth. During Solar Maximum, CMEs
are abundant and cosmic rays are held at bay. Now, however, the solar
cycle is approaching Solar Minimum, allowing cosmic rays to return.
Another reason could be the weakening of Earth's magnetic field, which
helps to protect us from deep-space radiation.
GROOVES ON PHOBOS EXPLAINED BY IMPACTS
University of California - Santa Cruz
Some of the unusual grooves on the surface of Mars' moon Phobos are
the result of debris ejected by impacts eventually falling back onto
the surface to form linear chains of craters, according to a new
study. One set of grooves on Phobos is thought to be a set of
stress fractures resulting from the tidal pull of Mars. A new
study addresses another set of grooves that is not fitted by that
explanation. Phobos is an unusual satellite, orbiting closer to
its planet than any other moon in the Solar System, with an orbital
period of just 7 hours 39 minutes. Small and heavily cratered, with
a lumpy non-spherical shape, it is only 9,000 km from the surface of
Mars and is slowly spiralling in towards the planet. Phobos appears
to have a weak interior structure covered by an elastic shell,
allowing it to be deformed by tidal forces without breaking apart.
Recent computer simulations showed how tidal stresses can cause
fracturing and linear grooves in the surface layer. Although that
idea was first proposed in the 1970s, the existence of so many grooves
with the wrong orientation for such stress fractures had remained
unexplained. Astronomers have now developed computer simulations
showing how the anomalous grooves could result from impacts. Material
ejected from the surface by an impact easily escapes the weak gravity
of Phobos. But the debris remains in orbit around Mars, most of it
moving either just slower or just faster than the orbital velocity of
Phobos, and within a few orbits it gets re-captured and falls back
onto the surface of the moon.
Simulations enabled researchers to track in precise detail the fate
of the ejected debris. It was found that re-captured debris create
distinctive linear impact patterns that match the characteristics of
the anomalous grooves and chains of craters that cut across the tidal
stress fractures on Phobos. The researchers used their model to match
a linear chain of small craters on Phobos to its primary source
crater. They simulated an impact at the 2.6-km crater Grildrig, near
the moon's north pole, and found that the pattern resulting from
ejected debris falling back onto the surface in the model was a very
close match to the actual crater chain observed on Phobos. With its
low mass and close orbit around Mars, Phobos is so unusual that it may
be the only place in the Solar System where such a phenomenon occurs.
NEW EXTREMELY DISTANT SOLAR-SYSTEM OBJECTS
Carnegie Institution for Science
In the race to discover a proposed ninth planet in our Solar System,
astronomers have observed several never-before-seen objects at extreme
distances from the Sun in our Solar System. The more objects that are
found at extreme distances, the better the chance of constraining the
location of the ninth planet that is predicted to exist far beyond
Pluto (itself no longer classified as a planet). The placement and
orbits of small, so-called extreme trans-Neptunian objects, can help
to narrow down the size and distance from the Sun of the predicted
ninth planet, because that planet's gravity influences the movements
of the smaller objects that are far beyond Neptune. The objects are
called trans-Neptunian because their orbits around the Sun are greater
than Neptune's. In 2014, astronomers announced the discovery of 2012
VP113 (nicknamed 'Biden'), which has the most-distant known orbit in
our Solar System. They also noticed that the handful of known extreme
trans-Neptunian objects have similar longitudes of perihelion. That
led them to predict that there is a planet at more than 200 times our
distance from the Sun. Its mass, ranging in possibility from several
Earths to a Neptune equivalent, is shepherding the smaller objects
into similar types of orbits. Some people have called it Planet X or
Planet 9. Further work since 2014 showed that such a massive ninth
planet probably exists, by further constraining its possible
properties. Analysis of 'neighbouring' small-body orbits suggest that
it is several times more massive than the Earth, possibly by as much
as 15 times, and at the closest point of its extremely elongated orbit
it is at least 200 AU from the Sun (over 5 times as distant as Pluto.)
Researchers are conducting a special survey for objects beyond Neptune
and the Kuiper Belt, and have covered nearly 10% of the sky to date.
As they find and confirm extremely distant objects, they analyze
whether their discoveries fit into the larger theories about how
interactions with a massive distant planet could have shaped the outer
Solar System. We are now in a situation similar to that in the
mid-19th century when Alexis Bouvard noticed Uranus' orbital motion
was peculiar, which eventually led to the discovery of Neptune. The
new objects submitted to the Minor Planet Center for designation
include 2014 SR349, which adds to the class of the rare extreme trans-
Neptunian objects. Its orbital characteristics are similar to those
of the previously known extreme bodies whose positions and movements
initially led astronomers to propose the influence of Planet X.
Another new-found extreme object, 2013 FT28, has some characteristics
similar to those of other extreme objects but also some differences.
2014 FE72 is the first distant Oort-Cloud object found with an orbit
entirely beyond Neptune. It has an orbit that takes the object so far
away from the Sun (3000 AU) that it is probably being influenced by
forces of gravity from beyond our Solar System such as those of other
stars and the Galactic tide. It is the first Solar-System object
observed at such a large distance.
ETA CARINAE'S 13th-CENTURY OUTBURST
University of Arizona
In the mid-1800s, astronomers surveying the night sky in the Southern
Hemisphere noticed that over the course of a few years, a previously
inconspicuous star named Eta Carinae grew brighter and brighter,
in 1843 outshining all other stars except Sirius, before fading
again over the next decade, becoming too dim to be seen with the naked
eye. The aftermath of the 'Great Eruption', which is now readily
visible through a small telescope, made Eta Carinae a celebrity
among celestial objects known for their bizarre beauty. An hour-
glass-shaped, billowing cloud of glowing gas and dust enshrouds the
star and its companion. Known as the Homunculus nebula, the cloud
consists of stellar material hurled into space during the Great
Eruption, drifting away at 2 million mph. By analysis of images of Eta
Carinae taken with the Hubble telescope, astronomers were surprised to
discover that the Great Eruption was only the latest in a series of
massive outbursts that have occurred since the 13th century. The
expansion rate of gas far outside the Homunculus indicates that it is
moving slowly and must have been ejected centuries before the observed
19th-century brightening. In fact, the motions of the outer material
point to two separate eruptions in the mid-13th and mid-16th
centuries. Although astronomers are prevented by the glowing gases of
the Homunculus nebula from getting a clear look at what's inside, they
have concluded that Eta Carinae is a binary system of two very massive
stars that orbit one another every 5.5 years. Both are much bigger
than the Sun and at least one of them is nearing the end of its life.
They are very large stars that appear very volatile, even when they
are not blowing off nebulae. They have dense cores and very tenuous
envelopes. If the Sun were replaced by the larger of the two, which
has about 90-100 solar masses, it could very well extend to the orbit
of Mars.
Because the Homunculus nebula is such an iconic and visually stunning
object, it has been a popular target of astronomical observations.
A total of eight images, taken over the course of two decades with
Hubble, has turned out to be a treasure trove for researchers. The
original goal of the observing programme was to measure proper
motions of stars and proto-stellar jets -- fast streams of matter
ejected by young stars during formation -- in the Carina Nebula, but
the same data also provided a powerful way to measure the motion of
debris ejected by Eta Carinae itself. By aligning the multi-epoch
images of the nebula, the team was able to track the movement of more
than 800 blobs of gas that Eta Carinae had ejected over time and to
derive a probable ejection date for each. The analysis showed that
the Homunculus nebula and the observed 19th-century brightening tell
only part of the story. Measuring the speed with which wisps of
ejected material expand outwards into space revealed that they must
have resulted from two separate eruptions that occurred about 600 and
300 years before the Great Eruption of the 19th century. In addition
to having separate origins in time, the older material also showed a
very different geometry from the Homunculus, where material was
ejected out from the star's poles and appears symmetrical about its
rotation axis. Though perplexing, the findings are a big step forward
for astronomers trying to understand what causes the outbursts. Eta
Carinae's eruptions provide some insight into the last unstable phases
of a very massive star's life. Researchers who study supernovae have
identified a sub-class of supernovae that appear to suffer violent
eruptions shortly before they finally explode. Eta Carinae may be our
nearest example of one.
STAR'S AGE IS DIFFICULT TO DETERMINE
NASA
For years, astronomers have puzzled over a massive star lodged deep in
the Milky Way that shows conflicting signs of being extremely old and
extremely young. Researchers initially classified the star as
elderly, perhaps a red supergiant. But a new study suggests that the
object, called IRAS 19312+1950, might be something quite different --
a proto-star, a star still in the making. Located more than 12,000
light-years away, the object first stood out as peculiar when it was
observed at particular radio frequencies. Several teams of astronomers
studied it with ground-based telescopes and concluded that it is an
oxygen-rich star about 10 times as massive as the Sun. The question
was: what kind of star? Some researchers favour the idea that the
star is evolved -- past the peak of its life cycle and on the decline.
For most of their lives, stars obtain their energy by fusing hydrogen
in their cores, as the Sun does now. But older stars have used up
most of their hydrogen and must rely on heavier elements that do not
last as long, leading to rapid deterioration. Two early clues --
intense radio sources called masers -- suggested that the star was
old. In astronomy, masers occur when excitation of the molecules in
certain gases causes them to emit a lot of radiation over a very
limited range of frequencies. The result is a powerful radio beacon
-- the microwave equivalent of a laser. One maser observed with IRAS
19312+1950 is almost exclusively associated with late-stage stars.
This is the silicon-oxide maser, produced by molecules made of one
silicon atom and one oxygen atom. Researchers do not know why that
type of maser is nearly always restricted to elderly stars, but of
thousands of known silicon-oxide masers, only a few exceptions to that
rule have been noted. Also observed with the star was a hydroxyl
maser, produced by molecules comprised of one oxygen atom and one
hydrogen atom. Hydroxyl masers can occur in various kinds of
astronomical objects, but when one occurs with an elderly star, the
radio signal has a distinctive pattern -- it is especially strong at a
frequency of 1612 megahertz. as was found in this case.
Even so, the object did not entirely fit with evolved stars. Specially
puzzling was the wide range of chemicals found in the large cloud of
material surrounding the star. Such a chemical-rich cloud is typical
of the regions where new stars are born, but no such stellar nursery
had been identified near this star. Scientists initially proposed
that the object was an old star surrounded by a surprising cloud
typical of the kind that usually accompanies young stars. Another
idea was that the observations might somehow be capturing two objects:
a very old star and an embryonic cloud of star-making material in the
same field. Astronomers began to reconsider the object, conducting
observations with the Herschel observatory and analyzing data
gathered earlier with the Spitzer telescope. Both telescopes operate
at infrared wavelengths, and gave the team new insight into the gases,
dust and ices in the cloud surrounding the star. The additional
information leads astronomers to think that the star is in a very
early stage of formation. The object is much brighter than it first
appeared, emitting about 20,000 times the energy of the Sun. The team
found large quantities of ices made from water and carbon dioxide in
the cloud around the object. The ices are located on dust grains
relatively close to the star, and all that dust and ice blocks out
starlight, making the star appear dimmer than it really is. Further-
more, the dense cloud around the object appears to be collapsing,
which happens when a growing star pulls in material. In contrast, the
material around an evolved star is expanding and is in the process of
escaping to the interstellar medium. The entire envelope of material
has an estimated mass of 500 to 700 Suns, which is much more than
could have been produced by an elderly or dying star. Also supporting
the idea of a young star are the very fast wind speeds measured in two
jets of gas streaming away from opposite poles of the star. Such jets
of material, known as a bipolar outflow, can be seen emanating from
young or old stars. However, fast, narrowly-focused jets are rarely
observed in evolved stars. In this case, the team measured winds at a
speed of at least 90 km/s -- a common characteristic of a proto-star.
Still, the researchers acknowledge that the object is not a typical
proto-star. For reasons they can't explain yet, the star has features
of both a very young and a very old star.
'RECENT' QUASAR ACTIVITY IN MILKY WAY
Harvard-Smithsonian Center for Astrophysics
The centre of the Milky Way galaxy is currently a quiet place where a
super-massive black hole slumbers, only occasionally devouring small
quantities of hydrogen gas. A new study shows that 6 million years
ago, the Galaxy's core blazed forth furiously. The evidence for such
an active phase came from a search for the Galaxy's missing mass.
About five-sixths of the mass of the Milky Way is in the form of
invisible and mysterious dark matter. The remaining one-sixth of our
galaxy's mass, or 150-300 billion solar masses, is normal
matter. However, if you count up all the stars, gas and dust we can
see, you find 'only' about 65 billion solar masses. The rest
of the normal matter -- stuff made of neutrons, protons, and electrons
-- seems to be missing. Scientists analyzed archival X-ray observa-
tions from the XMM-Newton spacecraft and found that the missing mass
is in the form of a million-degree gaseous fog permeating our Galaxy.
That fog absorbs X-rays from more distant background sources. The
astronomers tried to use the amount of absorption to calculate how
much normal matter was there, and how it was distributed. They
applied computer models, but found that they could not match the
observations with a smooth, uniform distribution of gas. Instead,
they found that there is a 'bubble' in the centre of the Galaxy that
extends two-thirds of the way out to the Sun. Clearing out that
bubble must have required a tremendous amount of energy. That energy,
the authors surmise, came from the feeding black hole. While some
infalling gas was swallowed by the black hole, other gas was pumped
out at speeds of 1,000 km/s.
Six million years later, the shock wave created by that phase of
activity has crossed 20,000 light-years of space. Meanwhile, the
black hole has run out of nearby food and gone into hibernation. That
time-line is corroborated by the presence of 6-million-year-old stars
near the Galactic Centre. Those stars formed from some of the same
material that once flowed towards the black hole. The different lines
of evidence all tie together very well -- the active phase lasted for
4 to 8 million years, which is reasonable for a quasar. The
observations and associated computer models also show that the hot,
million-degree gas can account for up to 130 billion solar
masses of material. Thus, it might explain where the Galaxy's missing
matter is hiding: it is too hot to be seen. More answers may come
from the proposed next-generation space mission known as X-ray
Surveyor. It would be able to map out the bubble by observing fainter
sources, and see finer detail to obtain more information about the
elusive missing mass. ESA's Athena X-ray Observatory, though not
planned for launch until 2028, offers similar promise.
SCIENTISTS DISCOVER A 'DARK' MILKY WAY
Yale University
Using the most powerful telescopes, an international team of
astronomers has found a massive galaxy that consists almost entirely
of dark matter. The galaxy, 'Dragonfly 44', is located in the
'nearby' Coma cluster and had been overlooked until last year because
of its unusual composition: it is a diffuse 'blob' about the size of
the Milky Way, but with far fewer stars. Astronomers used
observations from Keck, taken over six nights, to measure the
velocities of stars in the galaxy. Observations by the Gemini North
telescope revealed a halo of spherical clusters of stars around the
galaxy's core, similar to the halo that surrounds the Milky Way
galaxy. Star velocities are an indication of the galaxy's mass -- the
faster the stars move, the more mass its galaxy must have. The stars
in the galaxy move at velocities that are far greater than expected
for such a dim galaxy. It means that 'Dragonfly 44' has a huge amount
of unseen mass. Scientists initially observed the object with the
Dragonfly Telephoto Array. Dragonfly 44's mass is estimated to be
similar to that of the Milky Way. However, only one-hundredth of 1%
of it is in the form of stars and 'normal' matter. The other 99.99%
is in the form of dark matter -- a hypothesized material that remains
unseen but may make up more than 90% of the Universe. The researchers
note that finding a galaxy composed mainly of dark matter is not new;
ultra-faint dwarf galaxies have similar compositions. But those
galaxies were roughly 10,000 times less massive than Dragonfly 44.
Astronomers have no idea how galaxies like Dragonfly 44 could have
formed. The Gemini data show that a relatively large fraction of the
stars is in the form of very compact clusters, and that is probably an
important clue. Ultimately what we really want to learn is what dark
matter actually *is*. The race is on to find massive dark galaxies
that are even closer to us than Dragonfly 44, so that we can look for
feeble signals that may reveal a dark-matter particle.
LOST COMET LANDER IS FOUND
BBC Science
The lost comet-lander Philae is visible in new images downloaded
from the Rosetta probe in orbit around the icy comet 67P/Churyumov-
Gerasimenko. Philae was dropped on to the comet by Rosetta in 2014
but fell silent 60 hours later when its battery ran flat. Although
it relayed pictures and data to the Earth about its location, the
lander's actual resting place was a mystery. It was assumed that
Philae had bounced into a dark ditch on touchdown -- an analysis now
borne out by the latest pictures, which were acquired from a distance
of only 2.7 km from the comet. Rosetta had previously surveyed that
location -- dubbed Abydos -- without success. The discovery comes just
a few weeks before controllers plan to crash-land Rosetta itself on
to the comet, formally ending its mission. Although there is no hope
of reviving the lander -- some of its equipment will have been broken
in the cold of space -- simply knowing its precise resting place will
help scientists make better sense of the data it returned during its
three days of operation back in 2014.
SPITZER SPACE TELESCOPE BEGINS 'BEYOND' PHASE
NASA
Spitzer, which was launched on 2003 August 25, has consistently
adapted to new scientific and engineering challenges during its
mission, and the team expects that it will continue to do so during
the 'Beyond' phase, which will begin on October 1. The selected
research proposals for the Beyond phase, also known as Cycle 13,
include a variety of objects that Spitzer was not originally planned
to address -- such as galaxies in the early Universe, the black hole
at the centre of the Milky Way, and exo-planets. Spitzer has many
qualities that make it a valuable asset in exo-planet science,
including an extremely accurate star-targeting system and the ability
to control unwanted changes in temperature. Its stable environment
and ability to observe stars for long periods of time led to the first
detection of light from known exo-planets in 2005. Understanding the
early Universe is another area where Spitzer has broken ground.
Spitzer's Infrared Array Camera (IRAC) was designed to detect remote
galaxies roughly 12 billion light-years away -- so distant that
their light has been travelling for roughly 88% of the history of the
Universe. But now, thanks to collaborations between Spitzer and the
Hubble, scientists can see even further into the past. The farthest
galaxy ever seen, GN-z11, was characterized in a 2016 study of data
from those telescopes. GN-z11 is about 13.4 billion light-years
away; its light has been travelling since 400 million years after the
Big Bang.
Spitzer reinvented itself in 2009 May with its 'warm mission', after
the supply of liquid-helium coolant that was chilling its instruments
since 2003 August was exhausted. At the conclusion of the 'cold
mission', some of Spitzer's instruments stopped working effectively,
but two of the four cameras in IRAC persisted. Since then, the
spacecraft has made numerous discoveries despite operating in 'warmer'
conditions (which, at about -405°F or 30 K, are still very cold by
Earthly standards). Spitzer's Beyond mission phase will last until
the commissioning phase of the James Webb space telescope, currently
planned to be launched in 2018 October. Spitzer is going to identify
objects that Webb can later observe more intensely.
Topic: Mid September Astronomy Bulletin (Read 1318 times)