Topic: Early April Astronomy Bulletin

[Clive]

LESS RADIATION IN VAN ALLEN BELT WAS THAN BELIEVED
DOE/Los Alamos National Laboratory

Observations from NASA's Van Allen probes show that the fastest, most
energetic electrons in the inner radiation belt are actually much
rarer than scientists expected.  That is good news for spacecraft that
are orbiting in the region and can be damaged by high levels of
radiation.  The results will also help scientists to understand better
-- and detect -- effects from high-altitude nuclear explosions.  The
Van Allen belts are two doughnut-shaped regions of charged particles
encircling the Earth.  Past space missions have not been able to
distinguish electrons from high-energy protons in the inner radiation
belt.  But by using a special instrument, the 'Magnetic Electron and
Ion Spectrometer' (MagEIS), on the Van Allen probes, scientists could
look at the particles separately for the first time.  What they found
was surprising: almost none of the super-fast electrons -- the
relativistic electrons -- is present in the inner belt.  Scientists
have long understood that, of the two radiation belts, the outer belt
is the more active one.  During intense geomagnetic storms, when
charged particles from the Sun hurtle across the Solar System, the
outer radiation belt pulsates dramatically, growing and shrinking in
response to the pressure of the solar particles and magnetic field.
Scientists thought that the inner belt maintains a steady position
above the Earth's surface.  The new results, however, show that that
is not always true.  For example, during a very strong geomagnetic
storm in 2015 June, relativistic electrons were pushed deep into the
inner belt.

Given the rarity of the storms that can inject relativistic electrons
into the inner belt, the scientists now understand that lower levels
of radiation are typical there, a result that has implications for
spacecraft operating in that region.  Knowing exactly how much and
what type of radiation is present in any given region of space may
enable scientists and engineers to design lighter and cheaper
satellites tailored to withstand the specific radiation levels they
are liable to encounter.  That opens the possibility of doing science
that previously was not possible.  For example, we can now investigate
under what circumstances the electrons penetrate the inner region and
see if more intense geomagnetic storms give electron showers that are
more intense or more energetic.


MANY FACES OF COMET 67P 
NASA 

Images returned from ESA's Rosetta mission indicate that during its
most recent trip through the inner Solar System, the surface of comet
67P/Churyumov-Gerasimenko was a very active place -- full of growing
fractures, collapsing cliffs and massive rolling boulders.  Moving
material buried some features on the comet's surface while exhuming
others.  As comets approach the Sun, they undergo spectacular changes
on their surfaces.  That is something that we were not able really to
appreciate before the Rosetta mission, which gave us the chance to
look at a comet in ultra-high resolution for more than two years.
Most comets orbit the Sun in highly eccentric orbits that cause them
to spend most of their time in the extremely cold outer Solar System.
When a comet approaches the inner Solar System, the Sun begins to warm
the ice on and near the comet's surface.  When the ice warms enough it
can rapidly sublimate (turn directly from the solid to the vapour
state).  The sublimation process can occur with variable degrees of
intensity and time-scales and cause the surface to change rapidly.
Between 2014 August and 2016 September, Rosetta orbited comet 67P
during the comet's traverse of the inner Solar System.  (That was
about a third of the comet's 'year': its orbital period is about 6.45
years.)

Scientists saw a massive cliff collapse and a large crack in the
'neck' of the comet get bigger and bigger.  They discovered that a
huge 30-metre boulder had moved 140 metres from its original position
on the comet's nucleus.  The massive rock probably moved as a result
of several outburst events that were detected close to its original
position.  The warming of 67P also caused the comet's rotation rate to
speed up.  The comet's increasing spin rate in the lead-up to
perihelion is thought to be responsible for a 500-metre-long fracture
observed in 2014 August that runs through the comet's neck.  The
fracture was found to have increased in width by about 30 metres (100
feet) by 2014 December.  Furthermore, in images taken in 2016 June, a
new 150- to 300-metre fracture was identified parallel to the original
one.  The crack was extending -- indicating that the comet may split
up one day.  Understanding how comets change and evolve with time may
give us important insights into the types and abundance of ices in
comets, and how long comets can stay in the inner Solar System before
losing all their ice and becoming balls of dust.  That should helps us
understand better the conditions of the early Solar System, and
possibly even how life started.
 

PUREST, MOST MASSIVE BROWN DWARF
RAS

Astronomers have identified a record-breaking brown dwarf (a star too
small for nuclear fusion) with the 'purest' composition and the highest
mass yet known.  The object, known as SDSS J0104+1535, is a member of
the 'halo' -- the outermost reaches -- of our Galaxy, made up of the
most ancient stars.  Brown dwarfs are intermediate between planets and
fully-fledged stars.  Their masses are too small for full nuclear
fusion of hydrogen to helium (with a consequent release of energy) to
take place, but they are usually significantly more massive than
planets.  Located 750 light-years away in the constellation Pisces,
SDSS J0104+1535 is made of gas that is around 250 times purer than the
Sun -- it consists of more than 99.99% hydrogen and helium.  It is
estimated to have formed about 10 (US-)billion years ago; measurements
suggest that it has a mass equivalent to 90 times that of Jupiter,
making it the most massive brown dwarf found to date.  It was
previously not known if brown dwarfs could form from such primordial
gas, and the discovery points the way to a larger undiscovered
population of extremely pure brown dwarfs from our Galaxy's ancient
past.  SDSS J0104+1535 has been classified as an L-type ultra-subdwarf
from its optical and near-infrared spectrum, observed with ESO's VLT.


CLUES ABOUT MISSING GALAXIES
RAS

Astronomers have developed a way to detect the ultraviolet (UV)
background of the Universe, which could help explain why there are so
few small galaxies in the cosmos.  UV radiation is invisible but shows
up as visible red light when it interacts with gas.  Researchers have
now found a way to measure it using instruments on Earth.  The method
can be used to measure the evolution of the UV background through
cosmic time, mapping how and when it suppresses the formation of small
galaxies.  The study could also help to produce more accurate computer
simulations of the evolution of the Universe.  UV radiation is found
throughout the Universe and strips smaller galaxies of the gas that
forms stars, effectively stunting their growth.  It is believed to be
the reason why some larger galaxies like our Milky Way do not have
many smaller companion galaxies.  Simulations show that there should
be more small galaxies in the Universe, but UV radiation essentially
stopped them from developing by depriving them of the gas that they
need to form stars.  Larger galaxies like the Milky Way were able to
withstand the cosmic blast because of the thick gas clouds surrounding
them.  Massive stars and supermassive black holes produce huge amounts
of ultraviolet radiation, and their combined radiation builds up the
ultraviolet background.  The UV radiation excites the gas in the
Universe, causing it to emit red (H-alpha) light in a somewhat similar
way to that in which the gas in a fluorescent tube is excited.  The
research means that we can now measure and map the UV radiation, which
should help us to refine models of galaxy formation.
 
Researchers pointed the Multi-Unit Spectroscopic Explorer (MUSE), an
instrument on ESO's VLT in Chile, at the galaxy UGC 7321, which is 30
million light-years away.  MUSE provides a spectrum for each pixel in
the image, allowing the researchers to map the red light produced by
the UV radiation illuminating the gas in that galaxy.  The research
could also help scientists predict the temperature of the cosmic gas
with more accuracy.  Ultraviolet radiation heats the cosmic gas to
temperatures higher than that of the surface of the Sun.  Such hot gas
will not cool to make stars in small galaxies.  That explains why
there are so few small galaxies in the Universe, and also why our
Milky Way has so few small satellite galaxies.

 
FIVE NEW SUB-ATOMIC PARTICLES FOUND
BBC News

The Large Hadron Collider has discovered new sub-atomic particles that
could help to explain how the centres of atoms are held together.  The
particles are all different forms of the so-called Omega-c baryon,
whose existence was confirmed in 1994.  Physicists had always believed
that various types existed but had not been able to detect them until
now.  The discovery will shed light on the operation of the 'strong
force', which glues the insides of atoms.  The centres of atoms
consist of neutrons and protons.  They in turn are made up of smaller
particles called quarks, which have unusual names.  Those inside
neutrons and protons are called 'Up' and 'Down'.  The quarks are held
together by the nuclear 'strong force'.  Physicists have a theory
called quantum chromodynamics for how the nuclear strong force works,
but using it to make predictions requires very complex calculations.
The Omega-c baryon is in the same family of particles as the neutron
and proton, but it can be thought of as a more exotic cousin.  It too
is made up of quarks but they are called 'Charm' and 'Strange', and
they are heavier versions of the Up and Down quarks.  Since the
Omega-c particle's discovery, it was thought that there were heavier
versions -- its bigger brothers and sisters if you like.  Now,
physicists at the European Organization for Nuclear Research (CERN)
have found them.  They believe that, by studying those siblings, they
will learn more about the workings of the nuclear strong force.  The
discovery will shed light on how quarks bind together.  It may have
implications not only to understand protons and neutrons better, but
also more exotic multi-quark states, such as tetraquarks and
pentaquarks.


AROMATIC MOLECULES IN EARLY UNIVERSE
University of California - Riverside

Molecules found in car-engine exhaust fumes, that are thought to have
contributed to the origin of life on Earth, have made astronomers
seriously to underestimate the number of stars that were forming in
the early Universe.  The molecules are called polycyclic aromatic
hydrocarbons (PAH); they constitute a set that has more than a hndred
members.  On the Earth occur naturally in coal and tar; in space, they
are a component of the dust, which along with gas, fills the space
between stars within galaxies.  The study represents the first time
that astronomers have been able to measure variations of PAH emissions
in distant galaxies with different properties.  It has important
implications for the studies of distant galaxies because absorption
and emission of energy by dust particles can change astronomers' views
of distant galaxies.  The research was conducted as part of the
University of California-based MOSDEF survey, a study that uses the
Keck telescope in Hawaii to observe the content of about 1500 galaxies
seen as they were when the Universe was 1.5 to 4.5 billion years old.
The researchers observed the emitted visible-light spectra of a large
and representative sample of galaxies during the peak era of star-
formation activity in the Universe.  In addition, the researchers
incorporated infrared imaging data from the Spitzer and Herschel space
observatories to trace the polycyclic aromatic hydrocarbon emission in
mid-infrared bands and the thermal dust emission in far-infrared
wavelengths.

The researchers concluded that the emission of polycyclic aromatic
hydrocarbon molecules is suppressed in low-mass galaxies, which also
have a lower abundance of metals, by which they mean all atoms heavier
than hydrogen and helium.  Those results indicate that the polycyclic
aromatic hydrocarbon molecules are likely to be destroyed in the
hostile environment of low-mass and metal-poor galaxies with intense
radiation.  The researchers also found that the polycyclic aromatic
hydrocarbon emission is relatively weaker in young galaxies in
comparison with older ones, which may be because the relevant
molecules are not produced in large quantities in young galaxies.
They found that the star-formation activity and infrared luminosity in
the universe 10 billion years ago was approximately 30 per cent higher
than previous figures indicated.  Studying the properties of the
polycyclic aromatic hydrocarbon mid-infrared emission bands in the
distant Universe is of fundamental importance to improving our
understanding of the evolution of dust and chemical enrichment in
galaxies throughout cosmic time.  That will be one of the tasks of the
James Webb space telescope when it is launched next year.