SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 459 17 Dec 2017

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    The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 459  2017 December 17

      Here is the latest round-up of news from the Society for Popular  Astronomy.  http://www.popastro.com/
     
    JUNO SPACECRAFT OBSERVES JUPITER'S GREAT RED SPOT
    NASA

    Data collected by the Juno spacecraft during its first pass over Jupiter's
    Great Red Spot in 2017 July indicate that that iconic feature penetrates
    well below the clouds.  Other revelations from the mission include that
    Jupiter has two previously uncharted radiation zones. 

    Jupiter's Great Red Spot is a giant oval, in Jupiter's southern hemisphere,
    of crimson-coloured clouds that race counterclockwise around the oval's
    perimeter, with wind speeds greater than those in any storm on Earth.
    Measuring 16,000 kilometres as of 2017 April 3, the Great Red Spot is 1.3
    times as wide as the Earth.  The future of the Great Red Spot is still very
    much up for debate.  While the storm has been monitored since 1830, it has
    possibly existed for more than 350 years.  In the 19th century, the Great
    Red Spot was well over two Earths wide, but in modern times, it has appeared
    to be diminishing in size, as measured by spacecraft and Earth-based telescopes. 
    At the time that NASA's Voyagers 1 and 2 sped by Jupiter on their way to Saturn
    and beyond, in 1979, the Great Red Spot was twice the Earth's diameter.  Today,
    measurements by Earth-based telescopes indicate that the oval that Juno flew
    over has diminished in width by one-third and height by one-eighth since Voyager
    times.

    Juno also has detected a new radiation zone, just above the planet's
    atmosphere, near the equator.  The zone includes energetic hydrogen,
    oxygen and sulphur ions moving at almost light speed.  The new zone
    was identified by the Jupiter Energetic Particle Detector Instrument (JEDI)
    investigation.  The particles are believed to be derived from energetic neutral
    atoms in the gas around the moons Io and Europa.  The neutral atoms
    then become ions as their electrons are stripped away by interaction with
    the upper atmosphere of Jupiter.  Juno also found signatures of a high-
    energy heavy-ion population within the inner edges of Jupiter's relativistic-
    electron radiation belt — a region dominated by electrons moving close to
    the speed of light.  The signatures are observed during Juno's high-
    latitude encounters with the electron belt, in regions never explored by
    previous spacecraft.  The origin and exact species of those particles is
    not yet understood.  Juno's Stellar Reference Unit (SRU-1) star camera
    detects the signatures of that population as extremely-high-noise
    signatures in images collected by the mission's radiation-monitoring
    investigation.

    VOYAGER 1 FIRES UP THRUSTERS AFTER 37 YEARS
    NASA

    If you tried to start a car that's been sitting in a garage for decades, you
    might well expect the engine to fail to respond.  But a set of thrusters on
    the Voyager 1 spacecraft successfully fired up after 37 years without use.
    Voyager 1, NASA's farthest and fastest spacecraft, is the only man-made
    object in interstellar space, the environment between the stars.  The space-
    craft, which has been flying for 40 years, relies on small thrusters to
    orient itself so that it can communicate with the Earth.

    The thrusters fire in tiny pulses, or puffs, lasting mere milliseconds,
    to rotate the spacecraft slightly so that its antenna continues to point
    at our planet.  Now, the Voyager team is able to use a set of four backup
    thrusters, dormant since 1980.  The thrusters will be able to extend the
    life of the Voyager 1 spacecraft by two or three years.  Since 2014,
    engineers have noticed that the thrusters Voyager 1 has been using to orient
    itself, called 'attitude-control thrusters', have been degrading.  Over
    time, the thrusters require more puffs to produce the same amount of energy. 
    In the early days of the mission, Voyager 1 flew by Jupiter, Saturn, and
    important moons of each.  The thruster test went so well that the team will
    probably do a similar test on the thrusters of Voyager 2, a twin of Voyager 1. 
    The attitude-control thrusters currently used for Voyager 2 are not yet as
    degraded as Voyager 1's, however.  Voyager 2 is also on course to enter
    interstellar space, probably within the next few years.

    INFANT STARS FOUND NEAR MILKY WAY BLACK HOLE
    National Radio Astronomy Observatory

    At the centre of our Galaxy, in the immediate vicinity of its supermassive
    black hole, is a region wracked by powerful tidal forces and bathed in
    intense ultraviolet light and X-ray radiation.  Those harsh conditions,
    astronomers surmise, do not favour star formation, especially of low-mass
    stars like the Sun.  Surprisingly, new observations from the Atacama Large
    Millimetre/submillimetre Array (ALMA) suggest otherwise.  ALMA has revealed
    the telltale signs of eleven low-mass stars forming perilously close — within
    three light-years — to the Milky Way's supermassive black hole,
    known to astronomers as Sagittarius A* (Sgr A*).  At that distance, tidal
    forces driven by the supermassive black hole should be energetic enough to
    rip apart clouds of dust and gas before they can form stars.  The presence
    of the newly discovered proto-stars (the formative stage between a dense
    cloud of gas and a young, shining star) suggests that the conditions
    necessary to produce low-mass stars may exist even in one of the most
    turbulent regions of our Galaxy and possibly in similar locales throughout
    the Universe.  The ALMA data also suggest that the proto-stars are about
    6,000 years old.  The team of researchers identified the proto-stars by
    seeing the classic 'double lobes' of material that bracket each of them.
    Those cosmic hourglass-like shapes signal the early stages of star
    formation.  Molecules, like carbon monoxide (CO), in the lobes glow
    brightly in millimetre-wavelength light, which ALMA can observe with
    remarkable precision and sensitivity.  Proto-stars form from interstellar
    clouds of dust and gas.  Dense pockets of material in the clouds collapse
    under their own gravity and grow by accumulating more and more star-forming
    gas from their parent clouds.  A portion of the infalling material, however, never
    makes it onto the surface of the star.  Instead, it is ejected as a pair of high-velocity
    jets from the proto-star's north and south poles.  Extremely turbulent environments
    can disrupt the normal procession of material onto a proto-star, while intense radiation —
    from massive nearby stars and supermassive black holes — can blast away the
    parent cloud, thwarting the formation of all but the most massive of stars.

    The Milky Way's Galactic Centre, with its 4-million-solar-mass black hole,
    is located approximately 26,000 light-years from us in the direction of the
    constellation Sagittarius.  Vast stores of interstellar dust obscure that
    region, hiding it from optical telescopes.  Radio waves, however, including
    the millimetre and submillimetre light that ALMA sees, are able to penetrate
    the dust, giving radio astronomers a clearer picture of the dynamics and
    content of that hostile environment.  Previous ALMA observations of the
    region surrounding Sgr A* revealed multiple massive infant stars that are
    estimated to be about 6 million years old.  Those objects, known as
    proplyds, are common features in more placid star-forming regions, like the
    Orion Nebula.  Though the Galactic Centre is a challenging environment for
    star formation, it is possible for particularly dense cores of hydrogen gas
    to cross the necessary threshold and forge new stars.  For that to occur,
    outside forces would have to compress the gas clouds near the centre of the
    Galaxy to overcome the violent nature of the region and allow gravity to
    take over and form stars.  Astronomers speculate that high-velocity gas
    clouds could aid in star formation as they force their way through the
    interstellar medium.  It is also possible that jets from the black hole
    itself could be ploughing into the surrounding gas clouds, compressing
    material and triggering the burst of star formation.
     
    WATERLESS EXOPLANET HAS SMOTHERING STRATOSPHERE
    NASA

    Astronomers have found evidence that the oversized exoplanet WASP-18b is
    wrapped in a smothering stratosphere loaded with carbon monoxide and devoid
    of water.  The findings come from a new analysis of observations made by the
    Hubble and Spitzer space telescopes.  The formation of a stratosphere layer in
    a planet's atmosphere is attributed to 'sunscreen'-like molecules, which absorb
    ultraviolet (UV) and visible radiation coming from the star and then release that
    energy as heat.  The new study suggests that the 'hot Jupiter' WASP-18b, a
    massive planet that orbits very close to its host star, has an unusual composition,
    and the formation of that planet might have been quite different from that of Jupiter
    and gas giants in other planetary systems.  On the Earth, ozone absorbs UV in
    the stratosphere, protecting our world from a lot of the Sun's harmful radiation. 
    For the handful of exo-planets with stratospheres, the absorber is typically
    thought to be a molecule such as titanium oxide, a close relative of titanium
    dioxide, used on Earth as a paint pigment and sunscreen ingredient.  The
    researchers looked at data collected for WASP-18b, located 325 light-years
    from the Earth, as part of a survey to find exo-planets with stratospheres. 
    The heavyweight planet, which has the mass of 10 Jupiters, has been observed
    repeatedly, allowing astronomers to accumulate a relatively large trove of data. 
    The studyanalyzed five eclipses from archived Hubble data and two from Spitzer. 
    From the light emitted by the planet's atmosphere at infrared wavelengths, it is
    possible to identify the spectral fingerprints of water and some other important
    molecules.  The analysis revealed WASP-18b's peculiar fingerprint, which does
    not resemble that of any exo-planet examined so far.  To decide which molecules
    were most likely to match it, the team carried out extensive computer modelling.

    The findings indicate that WASP-18b has hot carbon monoxide in the stratosphere
    and cooler carbon monoxide in the layer of the atmosphere below (the troposphere). 
    The team determined that by detecting two types of carbon monoxide signatures,
    an absorption signature at a wavelength of about 1.6 microns and an emission
    signature at about 4.5 microns.  This is the first time that researchers have detected
    both types of signature for a single type of molecule in an exo-planet's atmosphere. 
    In theory, another possible fit for the observations is carbon dioxide, which has a
    similar fingerprint.  The researchers ruled that out because if there were enough
    oxygen available to form carbon dioxide, the atmosphere should also have some
    water vapour.  To produce the spectral fingerprints seen by the team, the upper
    atmosphere of WASP-18b would have to be loaded with carbon monoxide. 
    Compared to other hot Jupiters, the planet's atmosphere would probably contain
    300 times more 'metals', i.e. elements heavier than hydrogen and helium.  That
    extremely high metallicity would indicate that WASP-18b might have accumulated
    greater amounts of solid ices during its formation than Jupiter, suggesting that it
    may not have formed in the same way as other hot Jupiters.

    PROPER MOTIONS MEASURED FOR STARS OUTSIDE THE MILKY WAY
    University of Groningen

    By combining data from the Hubble Space Telescope and the Gaia mission,
    astronomers have been able to measure the proper motions of 15 stars in the
    Sculptor galaxy, the first such measurement of stars in a small galaxy
    outside the Milky Way.  Analysis shows an unexpected preference in the
    direction of movement, which suggests that the standard theoretical models
    used to describe the motion of stars and dark matter haloes in other
    galaxies might be invalid.  Astronomers have long been able to measure the
    movement of stars in our line of sight (i.e. the movement towards or away
    from us) by measuring the redshift, which is caused by the Doppler effect.
    However, measuring the movement in the plane of the sky, known as the
    proper motion, is much more difficult.  To detect that, you need multiple
    precise measurements of a star's position over the course of several years. 
    The immense distances involved mean that many stars in our Galaxy move
    very little across the sky when seen from Earth.  For stars outside the Galaxy,
    this movement is even less.  The European Gaia mission, which is currently
    under way, was designed to measure the exact location of more than one
    billion stars, mostly in our own Galaxy.  But Gaia also measures star positions
    in nearby galaxies, and for some of those stars, astronomers also have their
    location as measured by the Hubble Space Telescope, some 12 years ago.

    Astronomers set out to combine the two data sets.  That is not an easy task,
    as the two missions measure the location in different ways.  The team
    managed to combine the data by using background galaxies which did not
    change position in the 12 years.  They were of course very careful to
    minimize systematic errors, and out of 120 stars in the Sculptor Galaxy that
    were measured by both Hubble and Gaia they found extremely accurate
    paired observations for 15.  Next, they determined how the stars move in
    that small galaxy, which is quantified by the anisotropy parameter.  If it is
    high, the stars have very elongated trajectories, and if it is very small, they
    have circular orbits.  Knowing that allows astronomers to pin down the
    properties of the dark-matter halo in which the galaxy is embedded.  But
    the measured value was very surprising, as the standard models did not
    allow it.  That means that some of the assumptions on which the models
    are based must be wrong.  So far, it has only been possible to test models
    by using the line-of-sight movement.  That seemed fine, but now, with proper
    motion, the standard models are breaking down.  One possible explanation is
    that the models assume all stars to belong to a single population.  But we know
    that Sculptor is complex, with at least two stellar populations (one more compact
    and one more extended).  There is a model that includes that and does
    predict the anisotropy which the team observed, as long as most of the stars
    measured belong to the more compact population.  The movement of stars
    depends mostly on the invisible dark-matter halo around a galaxy.  That is
    why it is so important to determine the anisotropy parameter, because it can
    be used to pin down the distribution of dark matter in a galaxy, which in
    turn depends on the nature of dark matter itself. The present results show
    that by using the Gaia data, combined with other data sets, we can measure
    the proper motions of stars in galaxies outside the Milky Way and thus
    improve the models which describe how dark matter is distributed in those
    other galaxies.  A second major result is a more precise measurement of the
    orbit of the Sculptor Galaxy around the Milky Way.  That orbit is much
    bigger than expected.  Previously, it was believed that the current
    spheroidal shape of Sculptor was in part the result of some close passages,
    but the measurements show that that is not the case

    SEARCH FOR LIFE ON OTHER PLANETS MAY BE MORE DIFFICULT THAN EXPECTED
    RAS

    New simulations show that the search for life on other planets may well be
    more difficult than has previously been supposed.  A new study indicates that
    unusual air-flow patterns could hide atmospheric components from telescopic
    observations, with direct consequences for formulating the optimal strategy for
    searching for (oxygen-producing) life such as bacteria or plants on exo-planets. 
    Current hopes of detecting life on planets outside our own Solar System rest on
    examining the planets' atmospheres to identify chemical compounds that may
    be produced by living beings.  Ozone, a variety of oxygen, is one such molecule,
    and is seen as one of the possible tracers that may allow us to detect life on another
    planet from afar.  In the Earth's atmosphere, ozone forms a layer that protects us
    from the Sun's harmful UV radiation.  On an alien planet, ozone could be one piece
    in the puzzle that indicates the presence of oxygen-producing bacteria or plants.
    But now researchers at the Max Planck Institute for Astronomy in Germany
    have found that such tracers might be better hidden than we previously
    thought.  The team considered some of the nearest exo-planets that have the
    potential to be Earth-like: Proxima b, which is orbiting the star nearest to
    the Sun (Proxima Centauri), and the most promising of the TRAPPIST-1 family
    of planets, TRAPPIST-1d.  Those are examples of planets that orbit their host
    star in 25 days or less, and as a side effect have one side permanently facing
    their star and the other side permanently facing away.  Modelling the flow of air
    within the atmospheres of such planets, astronomers found that that unusual
    day-night divide can have a marked effect on the distribution of ozone across
    the atmosphere: at least for those planets, the major air flow may lead from the
    poles to the equator, systematically trapping the ozone in the equatorial region.

    Absence of traces of ozone in future observations does not have to mean that
    there is no oxygen at all.  It might be found in different places from where it is
    found on Earth, or it might be very well hidden.  Such unexpected atmospheric
    structures may also have consequences for habitability, given that most of the
    planet would not be protected against ultraviolet (UV) radiation.  In principle, an
    exo-planet with an ozone layer that covers only the equatorial region might still
    be habitable.  Proxima b and TRAPPIST-1d orbit red dwarfs, reddish stars that
    emit very little harmful UV light to begin with.  On the other hand, those stars
    can be very temperamental, and prone to violent outbursts of harmful radiation
    including UV.  The combination of advances in modelling and much better data
    from telescopes like the James Webb Space Telescope is likely to lead to
    significant progress in this exciting field.

    MILKY WAY ORBITS IN LOCAL SUPERCLUSTER
    University of Hawaii at Manoa

    A team of astronomers has produced the most detailed map ever of the orbits of
    galaxies in our extended local neighbourhood, showing the past motions of almost
    1,400 galaxies within 100 million light-years of the Milky Way.  The team reconstructed
    the galaxies' motions from 13 billion years in the past to the present day.  The main
    gravitational attractor in the mapped area is the Virgo Cluster, with 600 billion times
    the mass of the Sun, 50 million light years from us.  Over a thousand galaxies have
    already fallen into the Virgo Cluster, while in the future all galaxies that are currently
    within 40 million light years of the cluster will be captured.  Our Milky Way galaxy lies
    just outside the capture zone.  However, the Milky Way and Andromeda galaxies, each
    with 2 billion times the mass of the Sun, are destined to collide and merge in 5000
    million years.  For the first time, we are not only visualizing the detailed structure of
    our Local Supercluster of galaxies but we are seeing how the structure developed over
    the history of the Universe.  An analogy is the study of the current geography of the Earth
    from the movement of plate tectonics.  Such dramatic merger events are only part of a
    larger show.  There are two over-arching flow patterns within this volume of the Universe. 
    All galaxies in one hemisphere of the region — including our own Milky Way — are
    streaming towards a single flat sheet. In addition, essentially every galaxy over the
    whole volume is flowing, as a leaf would in a river, towards gravitational attractors at far
    greater distances.

    MOST DISTANT BLACK HOLE YET DISCOVERED
    NASA

    Scientists have uncovered a rare relic from the early Universe: the furthest
    known supermassive black hole.  That matter-eating beast is 800 million
    times the mass of our Sun and grew far larger than astronomers expected in
    only 690 million years after the Big Bang, which challenges theories about
    how black holes form.  Astronomers combined data from NASA's Wide-field
    Infrared Survey Explorer (WISE) with ground-based surveys to identify potential
    distant objects to study, then followed up with Carnegie Observatories' Magellan
    telescopes in Chile.  For black holes to become so massive in the early Universe,
    astronomers speculate that there must have been special conditions to allow
    rapid growth — but the underlying reason remains mysterious.  The newly found
    black hole is voraciously devouring material at the centre of a galaxy — a phenomenon
    called a quasar.  This quasar is especially interesting because it comes from a time
    when the Universe was just beginning to emerge from its dark ages.  The discovery
    will provide fundamental information about the Universe when it was only
    5 per cent of its current age.  Quasars are among the brightest and most
    distant known celestial objects and are crucial to understanding the early
    Universe.  The Universe began in a hot soup of particles that rapidly spread
    apart in a period called inflation.  About 400,000 years after the Big Bang,
    the particles cooled and coalesced into neutral hydrogen gas.  But the
    Universe stayed dark, without any luminous sources, until gravity condensed
    matter into the first stars and galaxies.  The energy released by the ancient
    galaxies caused the neutral hydrogen to ionize, or lose an electron.  The gas
    has remained in that state ever since that time.  Once the Universe became
    re-ionzed, photons could travel freely throughout space.  That is the point at
    which the Universe became transparent to light.  Much of the hydrogen surrounding
    the newly discovered quasar is neutral.  That means the quasar is not only the most
    distant — it is also the only example we have that can be seen before the Universe
    became re-ionized.  It has a redshift of 7.54, based on the detection of ionized carbon
    emissions.  That means that it took more than 13 billion years for the light from the quasar
    to reach us.  Scientists believe that the sky contains between 20 and 100 quasars as bright
    and as distant as that one.  Astronomers look forward to ESA's Euclid mission, and NASA's
    Wide-field Infrared Survey Telescope (WFIRST) mission, to find more such distant objects

    DEPTHS OF HUBBLE ULTRA DEEP FIELD
    ESO

    Astronomers using the MUSE instrument on the Very Large Telescope in Chile
    e have conducted the deepest spectroscopic survey ever.  They focussed on
    the Hubble Ultra-Deep Field, measuring distances and properties of 1600 very
    faint galaxies including 72 galaxies that had never been detected before, even
    by Hubble itself.  The original HUDF images were pioneering deep-field observations
    with the Hubble telescope, published in 2004.  They probed more deeply than ever
    before and revealed a menagerie of galaxies dating back to less than a billion years
    after the Big Bang.  The area was subsequently observed many times by Hubble
    and other telescopes, resulting in the deepest view of the Universe to date.  Now,
    despite the depth of the Hubble observations, MUSE has — among many other results —
    revealed 72 galaxies never seen before in that tiny area of the sky.  The MUSE data
    provide a new view of dim, very distant galaxies, seen near the beginning of the Universe.
    It has detected galaxies 100 times fainter than in previous surveys, adding to an already
    richly observed field and deepening our understanding of galaxies across the ages.  The
    survey unearthed 72 candidate galaxies known as Lyman-alpha emitters, that shine only
    in Lyman-alpha light.  Current understanding of star formation cannot fully explain those
    galaxies, which just seem to shine brightly at that one wavelength.  Because MUSE
    disperses the light into its component colours, those objects become apparent, but they
    remain invisible in deep direct images such as those from Hubble.  Another major
    finding of this study was the systematic detection of luminous hydrogen
    haloes around galaxies in the early Universe, giving astronomers a new and
    promising way to study how material flows into and out of early galaxies

    GRAVITATIONAL WAVES SHED LIGHT ON BLACK HOLES 
    Brown University

    A new study shows how scientists could use gravitational-wave experiments
    to test  the existence of primordial black holes, gravity wells formed just
    moments after the Big Bang, that some scientists have posited could be an
    explanation for dark matter.  Scientists know very well that black holes can
    be formed by the collapse of large stars, or as we have seen recently, the
    merger of two neutron stars, but it has been hypothesized that there could
    be black holes that formed in the very early Universe before stars existed
    at all.  The idea is that, shortly after the Big Bang, quantum-mechanical
    fluctuations led to the density distribution of matter that we observe today
    in the expanding Universe.  It has been suggested that some of those density
    fluctuations might have been large enough to result in black holes peppered
    throughout the Universe.  Such so-called primordial black holes were first
    proposed in the early 1970s by Stephen Hawking and collaborators, but
    have never been detected — it is still not clear whether they exist at all.  The
    ability to detect gravitational waves, as demonstrated recently by the Laser
    Interferometer Gravitational-Wave Observatory (LIGO), has the potential to
    shed new light on the issue.  Such experiments detect ripples in the fabric
    of space-time associated with major astronomical events like the collision
    of two black holes.  LIGO has already detected several black-hole mergers,
    and future experiments will be able to detect events that happened much
    further back in time.

    With future gravitational-wave experiments, cosmologists will be able to
    look back to a time before the formation of the first stars.  So if we see
    black-hole merger events before stars existed, then we will know that those
    black holes are not of stellar origin.  For this study, researchers
    calculated the redshift at which black hole mergers should no longer be
    detected if they are only of stellar origin.  They show that at a redshift
    of 40, which equates to about 65 million years after the Big Bang, merger
    events should be detected at a rate of no more than one per year, assuming
    stellar origin.  At redshifts greater than 40, events should disappear
    altogether.  In reality, merger events are expected to stop well before that
    point, but a redshift of 40 or so is the absolute hardest bound or cutoff
    point.  A redshift of 40 should be within reach of several proposed
    gravitational-wave experiments.  If they detect merger events beyond that,
    it means one of two things: either primordial black holes exist, or the
    early Universe evolved in a way that is very different from the standard
    cosmological model.  Either would be very important discoveries, the
    researchers say.  For example, primordial black holes fall into a category
    of entities known as MACHOs, or Massive Compact Halo Objects.  Some
    scientists have proposed that dark matter — the unseen stuff that is
    thought to comprise most of the mass of the universe — may be made of
    MACHOs in the form of primordial black holes.  A detection of primordial
    black holes would bolster that idea, while a non-detection would cast
    additional doubt upon it. The only other possible explanation for black-hole
    mergers at redshifts greater than 40 is that the Universe is 'non-Gaussian'.
    In the standard cosmological model, matter fluctuations in the early
    Universe are described by a Gaussian probability distribution.  A merger
    detection could mean that matter fluctuations deviate from a Gaussian
    distribution.  The rate at which detections are made past a redshift of 40
    — if indeed such detections are made — should indicate whether they are
    a sign of primordial black holes or evidence for non-Gaussianity.  But a
    non-detection would present a strong challenge to those ideas.

    MASSIVE PRIMORDIAL GALAXIES
    National Radio Astronomy Observatory

    Astronomers expect that the first galaxies, those that formed just a few
    hundred million years after the Big Bang, would share many similarities
    with some of the dwarf galaxies that we see in the nearby Universe today. 
    Those early agglomerations of a few thousand million stars would then
    become the building blocks of the larger galaxies that came to dominate the
    Universe after the first few thousand million years.  Ongoing observations with
    ALMA, however, have discovered surprising examples of massive, star-filled
    galaxies seen when the cosmos was less than a thousand million years old.
    That suggests that smaller galactic building blocks were able to assemble into
    large galaxies quite quickly.  The latest ALMA observations push back that epoch
    of massive-galaxy formation even further by identifying two giant galaxies seen
    when the Universe was 'only' 780 million years old, or about 5 per cent its current
    age.  ALMA also revealed that those uncommonly large galaxies are nestled inside
    an even-more-massive cosmic structure, a halo of dark matter several billion times
    as massive as the Sun.  The two galaxies are in such close proximity — less than the
    distance from the Earth to the centre of our Galaxy — that they will shortly merge to
    form the largest galaxy ever observed at that period in cosmic history.  This discovery
    provides new details about the emergence of large galaxies and the role that dark
    matter plays in assembling the most massive structures in the Universe.

    The galaxies that researchers have studied, collectively known as
    SPT0311-58, were originally identified as a single source by the South Pole
    Telescope.  The first observations indicated that that object was very
    distant and glowing brightly in infrared light, meaning that it was
    extremely dusty and likely to be going through a burst of star formation.
    Subsequent observations with ALMA revealed the distance and dual nature
    of the object, clearly resolving the pair of interacting galaxies.  To make
    that observation, ALMA had some help from a gravitational lens, which
    provided an observing boost to the telescope.  Gravitational lenses form
    when an intervening massive object, like a galaxy or galaxy cluster, bends
    the light from more distant galaxies.  They do, however, distort the
    appearance of the object being studied, requiring sophisticated computer
    models to reconstruct the image as it would appear in its unaltered state.
    That 'de-lensing' process provided intriguing details about the galaxies,
    showing that the larger of the two is forming stars at a rate of 2,900 solar
    masses per year.  It also contains about 270 billion times the mass of
    our Sun in gas and nearly 3 billion times the mass of our Sun in dust.
    The astronomers determined that that galaxy's rapid star formation was
    probably triggered by a close encounter with its slightly smaller companion,
    which already hosts about 35 billion solar masses of stars and is
    increasing its rate of starburst at the breakneck pace of 540 solar masses
    per year.  The researchers note that galaxies of that era are 'messier' than
    the ones we see in the nearby Universe.  Their more jumbled shapes would
    be due to the vast stores of gas raining down on them and their ongoing
    interactions and mergers with their neighbours.  The new observations also
    allowed the researchers to infer the presence of a truly massive dark-matter
    halo surrounding both galaxies.  Dark matter provides the pull of gravity
    that causes the Universe to collapse into structures (galaxies, groups and
    clusters of galaxies, etc.).  By comparing their calculations with current
    cosmological predictions, the researchers found that this halo is one of the
    most massive that should exist at that time.

    Bulletin compiled by Clive Down (c) 2017  The Society for Popular Astronomy
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