The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 430 Sept 25th

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    The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 430 2016 September 25

    Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is arguably Britain's liveliest astronomical society, with members all over the world. We accept subscription payments online at our secure site and can take credit and debit cards. You can join or renew via a secure server or just see how much we have to offer by visiting http://www.popastro.com/

    ASTEROID BUZZES EARTH, HEADS FOR MOON
    Spaceweather.com

    Newly discovered asteroid 2016 RB1 flew past the Earth on Sept. 7,
    only 25,000 miles above the South Pole. Because of the asteroid's
    southern trajectory, it did not pass within the orbits of any
    communication or weather satellites — but it was close. After it
    passed by the Earth, the space rock turned and headed for the Moon,
    executing a wider fly-by at 179,000 miles on Sept. 8. Researchers
    say that 2016 RB1 is about 50 feet in diameter. Astronomers used a
    remotely-controlled telescope at Siding Spring, in Australia, to
    photograph the asteroid as it was approaching the Earth on Sept. 7.
    It looked like a 12th-magnitude star. The asteroid spends all of its
    time in the inner Solar System. In 2017 October it will fly by Venus,
    and will do so again in 2020 March before it returns towards the Earth
    in June of that year. None of those encounters is expected to result
    in an impact.
    Asteroid 2016 RB1 was discovered on Sept. 5 by astronomers using the
    60-inch Cassegrain reflector of the Catalina Sky Survey, on Mount
    Lemmon in the Catalina Mountains north of Tucson, Arizona.

    ASTRONOMERS OBSERVE DISINTEGRATING COMET
    University of California, Los Angeles

    Astronomers using the Hubble telescope have obtained detailed
    observations of a comet breaking apart 67 million miles from the
    Earth. In a series of images taken over three days in 2016 January,
    Hubble showed 25 fragments consisting of a mixture of ice and dust
    that are drifting away from the comet at a rate similar to walking
    speed. The images suggest that the roughly 4.5-billion-year-old
    comet, named 332P/Ikeya-Murakami, or comet 332P, may be spinning so
    fast that material is ejected from its surface. The resulting debris
    are now scattered along a 3,000-mile-long trail. The observations
    provide insight into the volatile behaviour of comets as they approach
    the Sun and begin to vaporize. The three-day observations show that
    the comet shards brighten and dim as icy patches on their surfaces
    rotate into and out of sunlight. Their shapes change, too, as they
    break apart. The icy relics comprise about 4% of the parent comet and
    range in size from about 20 to 60 metres. The Hubble images show that
    the parent comet changes brightness frequently, completing a rotation
    every two to four hours. The comet is much smaller than astronomers
    originally thought, measuring only about 500 m across. Comet 332P was
    discovered in 2010 November by two Japanese amateur astronomers, after
    it surged in brightness. From the Hubble data, the research team
    suggests that sunlight heated the surface of the comet, causing it to
    expel jets of dust and gas. The jets act like rocket engines,
    spinning up the comet's rotation. The faster spin rate loosened
    chunks of material, which are drifting off into space. The research
    team calculated that the comet probably shed material over a period of
    months, between October and December last year. The researchers
    estimate that comet 332P has enough mass for 25 more outbursts. If
    the comet has an episode every six years, the equivalent of one orbit
    around the Sun, then it will be gone in 150 years.

    PLUTO 'PAINTS' ITS LARGEST MOON RED
    NASA

    In 2015 June, when the cameras on the approaching New Horizons
    spacecraft first observed the large reddish polar region on Pluto's
    largest moon, Charon, mission scientists had never seen anything like
    it elsewhere in the Solar System, and they couldn't wait to get the
    story behind it. Over the past year, after analyzing the images and
    other data that New Horizons has sent back from its historic 2015 July
    flight through the Pluto system, the scientists think they understand
    why the polar region on Pluto's largest moon, Charon, is red. The
    colouring comes from Pluto itself — as methane gas that escapes from
    Pluto's atmosphere and becomes 'trapped' by the moon's gravity and
    freezes to the cold, icy surface at Charon's pole. That is followed
    by chemical processing by ultraviolet light from the Sun that
    transforms the methane into heavier hydrocarbons and eventually into
    reddish organic materials called tholins. The team combined analyses
    from detailed Charon images obtained by New Horizons with computer
    models of how ice evolves at Charon's poles. Mission scientists had
    previously speculated that methane from Pluto's atmosphere was trapped
    at Charon's north pole and slowly converted into the reddish material,
    but had no models to support that theory. The New Horizons team tried
    to determine whether conditions on the Charon (which has a diameter of
    1,212 km) could allow the capture and processing of methane gas. The
    models using Pluto and Charon's 248-year orbit around the Sun show
    some extreme weather at Charon's poles, where 100 years of continuous
    sunlight alternate with a century of continuous darkness. Surface
    temperatures during those long winters dip to -257 C, cold enough to
    freeze methane solid.
    The methane molecules bounce around on Charon's surface until they
    either escape back into space or land on the cold pole, where they
    freeze solid, forming a thin coating of methane ice that lasts until
    sunlight comes back in the spring. But while the methane ice quickly
    sublimates away, the heavier hydrocarbons created from it remain on
    the surface. Sunlight further irradiates those leftovers into reddish
    material — called tholins — that has slowly accumulated on Charon's
    poles over millions of years. New Horizons' observations of Charon's
    other pole, currently in winter darkness — and seen by New Horizons
    only by light reflected from Pluto, or 'Pluto-shine' — confirmed
    that the same activity was occurring at both poles. This study solves
    one of the greatest mysteries astronomers found on Charon, Pluto's
    giant moon, and opens up the possibility that other small planets in
    the Kuiper Belt with moons may create similar, or even more extensive,
    'atmospheric transfer' features on their moons.

    ASTRONOMERS OBSERVE STAR REBORN IN A FLASH
    RAS

    Using the Hubble telescope, astronomers have been able to study
    stellar evolution in real time. Over a period of 30 years dramatic
    increases in the temperature of the star SAO 244567 have been
    observed. Now the star is cooling again, having been reborn into an
    earlier phase of stellar evolution. That makes it the first reborn
    star to have been observed during both the heating and cooling stages
    of rebirth. Even though the Universe is constantly changing, most
    processes are too slow to be observed within a human life-span. The
    new work shows an exception to that rule. SAO 244567 is one of the
    rare examples of a star that allows us to witness stellar evolution in
    real time. Over only twenty years the star has doubled its
    temperature, and it was possible to watch the star ionizing its
    previously ejected envelope, which is now known as the Stingray
    Nebula. SAO 244567, 2,700 light-years from the Earth, is the central
    star of the Stingray Nebula, and has been visibly evolving between
    observations made over the last 45 years. Between 1971 and 2002 the
    surface temperature of the star skyrocketed by almost 40,000°C. Now
    new observations made with the Cosmic Origins spectrograph on the
    Hubble telescope have revealed that SAO 244567 has started to cool and
    expand. That is unusual, though not unheard-of, and the rapid heating
    could easily be explained if one assumed that SAO 244567 had an
    initial mass of 3 to 4 times the mass of the Sun. However, the data
    show that SAO 244567 must have had an original mass similar to that of
    our Sun. Such low-mass stars usually evolve on much longer time-
    scales, so the rapid heating has been a mystery for decades.
    In 2014 the team proposed a theory that resolved the issue of both SAO
    244567's rapid increase in temperature as well as the low mass of the
    star. They suggested that the heating was due to what is known as a
    helium shell-flash event: a brief ignition of helium outside the
    stellar core. That theory has very clear implications for SAO
    244567's future: if it has indeed experienced such a flash, then it
    would force the central star to begin to expand and cool again — it
    would return back to the previous phase of its evolution. That is
    exactly what the new observations confirm. The release of nuclear
    energy by the flash forces the already very compact star to expand
    back to giant dimensions — the born-again scenario. It is not the
    only example of such a star, but it is the first time that a star has
    been observed during both the heating and cooling stages of such a
    transformation. Astronomers need refined calculations to explain some
    still mysterious details in the behaviour of SAO 244567. Those could
    not only help them to understand the star itself better but could also
    provide a deeper insight into the evolution of the central stars of
    planetary nebulae.

    HUNDREDS OF UNDISCOVERED BLACK HOLES
    University of Surrey
    New research has shone light on a globular cluster of stars that could
    host several hundred black holes, a phenomenon that until recently was
    thought impossible. Globular clusters are spherical collections of
    stars which orbit around a galactic centre such as that of our Milky-
    Way galaxy. Using computer simulations, astronomers were able to see
    the un-seeable by mapping the globular cluster NGC 6101, from which
    the existence of black holes within the system was deduced. The black
    holes are a few times larger than the Sun, and form in the gravita-
    tional collapse of massive stars at the end of their lives. It was
    previously thought that such black holes would almost all be expelled
    from their parent cluster owing to the effects of supernova explo-
    sions, during the death of a star. Black holes are impossible to see
    with a telescope, because no photons can escape. In order to find
    them astronomers look for their gravitational effect on their
    surroundings. Using observations and simulations they are able to
    spot the distinctive clues to their whereabouts and therefore
    effectively 'see' the un-seeable. It is only as recently as 2013 that
    astrophysicists found individual black holes in globular clusters
    through rare phenomena in which a companion star donates material to
    the black hole. That work has shown that in NGC 6101 there could be
    several hundred black holes, overturning old theories as to how black
    holes form.
    The work is intended to help answer fundamental questions related to
    dynamics of stars and black holes, and the recently observed
    gravitational waves. Those are emitted when two black holes merge,
    and if the interpretation is right, the cores of some globular
    clusters may be where black-hole mergers take place. The researchers
    chose to map that particular ancient globular cluster because of its
    recently-found distinctive make-up, which suggested that it could be
    different from other clusters. Compared with other globular clusters,
    NGC 6101 appears dynamically young, in contrast to the ages of the
    individual stars. Also the cluster appears inflated, with the core
    being under-populated by observable stars. Using computer simulation,
    the team recreated every individual star and black hole in the cluster
    and their behaviour. Over the whole lifetime of thirteen billion
    years the simulation demonstrated how NGC 6101 has evolved. It was
    possible to see the effects of large numbers of black holes on the
    visible stars, and to reproduce what was observed in NGC 6101. From
    that, the researchers showed that the otherwise inexplicable dynamical
    apparent youth is an effect of the large black-hole population. The
    results show that globular clusters like NGC 6101, which were always
    considered boring, are in fact the most interesting ones, possibly
    each harbouring hundreds of black holes.

    RARE FOSSIL RELIC OF MILKY WAY
    ESO

    Astronomers have found a fossilized remnant of the early Milky Way
    harbouring stars of hugely different ages. That stellar system
    resembles a globular cluster, but is like no other cluster known.
    It contains stars remarkably similar to the most ancient stars in the
    Milky Way, and bridges the gap in understanding between our Galaxy's
    past and its present. Terzan 5, 19,000 light-years distant in the
    constellation Sagittarius (the direction of the Galactic Centre), has
    been classified as a globular cluster for the 40-odd years since its
    detection. Now, an Italian-led team has discovered that Terzan 5 is
    like no other globular cluster known. The team scoured data from the
    'Multi-conjugate Adaptive Optics Demonstrator' installed on the VLT,
    as well as from a suite of other ground-based and space telescopes.
    They found compelling evidence that there are two distinct kinds of
    stars in Terzan 5 which not only differ in the elements they contain,
    but have an age gap of roughly 7 billion years. The ages of the
    two populations indicate that the star-formation process in Terzan 5
    was not continuous, but was dominated by two distinct bursts. That
    requires the Terzan 5 ancestor to have large amounts of gas for a
    second generation of stars and to have a mass at least 100 million
    times the mass of the Sun. Its unusual properties make Terzan 5 the
    ideal candidate for a fossil from the early days of the Milky Way.
    Current theories on galaxy formation assume that vast clumps of gas
    and stars interacted to form the primordial bulge of the Milky Way,
    merging and dissolving in the process. Some remnants of such gaseous
    clumps could remain relatively undisrupted and keep existing, embedded
    within the Galaxy. Such galactic fossils allow astronomers to
    reconstruct an important piece of the history of our Milky Way.
    While the properties of Terzan 5 are uncommon for a globular cluster,
    they are very similar to those of the stellar population which can be
    found in the Galactic bulge, the tightly packed central region of the
    Milky Way. Those similarities could make Terzan 5 a fossilized relic
    of galaxy formation, representing one of the earliest building blocks
    of the Milky Way. That idea is strengthened by the original mass of
    Terzan 5 necessary to create two stellar populations — a mass similar
    to those of the huge clumps which are assumed to have formed the bulge
    during galaxy assembly around 12 billion years ago. Somehow Terzan 5
    has managed to survive being disrupted for billions of years, and has
    been preserved as a remnant of the distant past of the Milky Way.
    Some characteristics of Terzan 5 resemble those detected in the giant
    clumps we see in star-forming galaxies at high redshift, suggesting
    that similar assembling processes occurred in the local and in the
    distant Universe at the epoch of galaxy formation. Hence, this
    discovery paves the way for a better and more complete understanding
    of galaxy assembly. Terzan 5 could represent an intriguing link
    between the local and the distant Universe, a surviving witness of the
    Galactic-bulge assembly process.

    BLACK HOLE CHANGES BEHAVIOUR
    ESO

    The mystery of a rare change in the behaviour of a super-massive
    black hole at the centre of a distant galaxy has been solved by an
    international team of astronomers using the VLT along with the Hubble
    telescope and the Chandra X-ray observatory. It seems that the black
    hole has fallen on hard times and is no longer being fed enough fuel
    to make its surroundings shine. Many galaxies are found to have
    extremely bright cores powered by supermassive black holes. The cores
    make 'active galaxies' some of the brightest objects in the Universe.
    They are thought to shine so brightly because hot material is glowing
    fiercely as it falls into the black hole, a process known as
    accretion. The brilliant light can vary hugely between different
    active galaxies, so astronomers classify them into several types on
    the basis of the properties of the light they emit. Some of such
    galaxies have been observed to change dramatically over the course of
    only 10 years — a blink of an eye in astronomical terms. However,
    the active galaxy in the new study, Markarian 1018, stands out by
    having changed type a second time, reverting back to its initial
    classification within the last five years. A handful of galaxies has
    been observed to make such a full-cycle change, but never before has
    one been studied in such detail. The discovery of Markarian 1018's
    fickle nature was a chance by-product of the Close AGN Reference
    Survey (CARS), a collaborative project to gather information on 40
    nearby galaxies with active cores. Routine observations of Markarian
    1018 with the Multi-Unit Spectroscopic Explorer (MUSE) on the VLT
    revealed the surprising changes in the light output of the galaxy.
    The chance observation of the galaxy so soon after it began to fade
    was an unexpected opportunity to learn what makes such galaxies tick.
    Astronomers were lucky to have detected the event just 3-4 years after
    the decline started, so they could begin monitoring campaigns to study
    details of the accretion physics of active galaxies that cannot be
    studied otherwise. The research team made the most of that
    opportunity, making it their first priority to pinpoint the process causing
    Markarian 1018's brightness to change so wildly. That could have been
    caused by any one of a number of astrophysical events, but they could
    rule out the black hole pulling in and consuming a single star and
    cast doubt on the possibility of obscuration by intervening gas.
    But the true mechanism responsible for Markarian 1018's surprising
    variation remained unsolved after the first round of observations.
    However, the team was able to gather extra data after being awarded
    observing time to use the Hubble telescope and the Chandra X-ray
    observatory. With the new data it was able to solve the mystery —
    the black hole was slowly fading because it was being starved of
    accretion material. It is possible that that starvation is because
    the inflow of fuel is being disrupted, and an intriguing possibility
    is that that could be due to interactions with a second supermassive
    black hole. Such a black-hole binary system is a distinct possibility
    in Markarian 1018, as the galaxy is the product of a major merger of
    two galaxies, each of which probably contained a super-massive black
    hole in its centre.

    GAIA TELESCOPE PLOTS ONE BILLION STARS
    BBC Science

    Astronomers using the Gaia space telescope have released a first
    tranche of data recording the positions and brightnesses of over a
    billion stars. For some two million of those objects, their
    distance and sideways motion across the heavens have also been
    accurately plotted. Gaia's mapping effort is already unprecedented in
    scale, but it still has several years to run. Remarkably, scientists
    say the store of information even now is too big for them to sift,
    and they are appealing for the public's help in making discoveries.
    To give one example of the scope of Gaia, of the 1.1 billion light
    sources in the data release, something like 400 million have never
    been recorded in any previous catalogue. A web portal has been opened
    where anyone can play with Gaia data and look for novel phenomena.
    The European Space Agency launched the Gaia mission in 2013; its goal
    was to update and extend the work of the Hipparcos satellite from the
    1990s, which mapped the positions, brightnesses, distances and proper
    motions of 100,000 stars. Gaia, with its first release of data, has
    just increased that haul 20-fold. The new mission actually carries
    two telescopes, which it scans across the Milky Way from a location
    about 1.5 million km from the Earth. The telescopes' mirrors form an
    image on a 1 billion-pixel camera detector connected to a trio of
    instruments. The specification was to determine the brightest
    objects' coordinates within an error of just seven micro-arcseconds.
    In addition to their positions and proper motions, the stars are
    having their physical properties analyzed by Gaia. Not all of that
    information can be gleaned at once. It will take repeat viewing, but
    by the end of five years of operations the 100,000 stars fully
    profiled by Hipparcos should become at least a billion in the Gaia
    catalogue.
    If one thing is clear from the new data it is that Gaia is seeing many
    more faint stars than anyone anticipated. Once the project is
    complete it may have plotted 2-3 billion light sources. One
    eagerly anticipated measurement is the radial velocity of stars, which
    describe the movements they make towards or away from Gaia. If that
    measurement is combined with the stars' proper motions, it will lay
    bare the dynamics of the Milky Way. It should be possible, for
    example, to make a kind of time-lapse movie — to run forwards to see
    how the Galaxy might evolve into the future, or to run backwards to
    see how our cosmic neighbourhood came to be the shape it is today. At
    the outset of the mission, scientists had hoped to get radial-velocity
    data on about 150 million stars. But that was thrown into doubt when
    it was realized, soon after Gaia's launch, that unexpected stray light
    was getting into the telescope. That made the observation of the
    faintest stars and their colours far more challenging. Engineers now
    think that they understand the problem: in part it is caused by the
    way sunlight diffracts past the 10-metre shade that Gaia uses to keep
    its telescopes in shadow. The good news according to the scientists
    is that they think they can work around the difficulties. The longer
    the mission runs, they believe, the closer will Gaia get to its target
    of 150 million radial-velocity measurements.

    CASSINI BEGINS FINAL YEAR AT SATURN
    NASA
    After more than 12 years studying Saturn, its rings and moons, the
    Cassini spacecraft has entered the final year of its voyage. The
    conclusion of the historic scientific odyssey is planned for 2017
    September, but not before the spacecraft completes a daring two-part
    end-game. Beginning on November 30, Cassini's controllers will send
    the spacecraft just past the outer edge of the main rings, starting a
    series of 20 orbits, called the F-ring orbits. During those weekly
    orbits, Cassini will approach to within 7,800 kilometres of the centre
    of the narrow F ring, with its peculiar kinked and braided structure.
    During the F-ring orbits astronomers expect to see the rings, along
    with the small moons and other structures embedded in them, as never
    before. Cassini's final phase — called the Grand Finale — begins
    next April. A close fly-by of Saturn's large moon Titan will re-shape
    the spacecraft's orbit so that it passes through the gap between
    Saturn and the rings – an unexplored space only about 2,400 kilometres
    wide. The spacecraft is expected to make 22 plunges through that gap.
    During the Grand Finale, Cassini will make the closest-ever observa-
    tions of Saturn, mapping the planet's magnetic and gravity fields and
    returning ultra-close views of the atmosphere. Scientists also hope
    to gain new insights into Saturn's interior structure, the precise
    length of a Saturn day, and the total mass of the rings — which may
    finally help settle the question of their age. The spacecraft will
    also make direct analyses of dust-sized particles in the main rings
    and sample the outer reaches of Saturn's atmosphere — both first-
    time measurements for the mission. The Grand Finale will come to a
    dramatic end on 2017 September 15, as Cassini dives into Saturn's
    atmosphere, returning data about the planet's chemical composition
    until its signal is lost. Friction with the atmosphere will cause
    the spacecraft to burn up like a meteor soon afterwards.

    Bulletin compiled by Clive Down
    (c) 2016 The Society for Popular Astronomy
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