SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 436 2016 December

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    Electronic News Bulletin No. 436 2016 December 18

    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
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    Catholic University of Leuven

    What will happen to the Earth when, in a few billion years' time, the
    Sun is a hundred times bigger than it is today? Using the most powerful
    radio telescope in the world, an international team of astronomers has
    set out to look for answers in the star L2 Puppis. Five billion years ago,
    that star was very similar to the Sun as it is today. Five billion years from
    now, the Sun will have grown into a red giant star, more than a hundred
    times larger than its current size. It will also experience intense mass
    loss through a very strong stellar wind. The end product of its
    evolution, 7 billion years from now, will be a tiny white-dwarf star.
    That will be about the size of the Earth, but much more massive:
    a teaspoonful of white-dwarf material has a mass of about 5 tons.
    That metamorphosis will have a dramatic impact on the planets of
    the Solar System. Mercury and Venus will be engulfed by the giant
    Sun and destroyed, but the fate of the Earth is still uncertain.
    We already know that the Sun will be much bigger and brighter, so it
    will probably destroy all forms of life on our planet. But will the
    Earth's rocky core survive the red-giant phase and continue orbiting
    the white dwarf?
    In an effort to answer that question, an international team of astro-
    nomers observed the evolved star L2 Puppis. That star is 208 light-
    years away — which in astronomical terms is nearby. The researchers
    used the ALMA radio telescope, which consists of 66 individual radio
    antennae that together contitute a telescope with a diameter of 16
    kilometres. They discovered that L2 Puppis is about 10 billion years
    old. Five billion years ago, that star was an almost perfect twin of
    the Sun as it is today, with the same mass. One third of its mass was
    lost during the evolution of the star. The same will happen with the
    Sun in the very distant future. 300 million kilometres from L2 Puppis
    — twice the distance between the Sun and the Earth — the researchers
    detected an object orbiting the giant star. In all likelihood, it is
    a planet that offers a unique preview of our Earth five billion years
    from now. A deeper understanding of the interactions between L2
    Puppis and its planet should yield interesting information on the
    final evolution of the Sun and its impact on the planets in the Solar
    System. Whether the Earth will eventually survive the Sun or be
    destroyed is still uncertain; L2 Puppis may be the key to answering
    that question.

    Cornell University

    Freshly harvested data from the Cassini mission reveal that Saturn's
    moons may be younger than previously thought. Members of the Europe-
    based Encelade scientific team that pored over the Cassini data
    provided two key measurements in the research: the rigidity of the
    tidal bulge, or the Love number — named for Augustus E.H. Love, a
    distinguished British mathematician who studied elasticity — and the
    dissipation factor, which controls the speed at which moons move away.
    While Saturn is mostly a gigantic shroud of liquid hydrogen and liquid
    helium, it contains a rocky core about 18 times the size of the Earth,
    which responds to tidal forces from all of Saturn's major moons by
    bulging. The forces of the bulging core, in turn, push the moons
    slightly away. The two parameters — the Love number and dissipation
    factor — are difficult to separate. So the team detected and exam-
    ined the orbits of four tiny moons associated with the larger moons
    Tethys (Telesto and Calypso) and Dione (Helene and Polydeuces). While
    those tiny moons produce neglible tidal forces on Saturn, their orbits
    are disturbed by the tidal bulges of Saturn's core. By monitoring the
    disturbances, the team managed to obtain the first measurement of
    Saturn's Love number and distinguish it from the dissipation factor.
    The moons are migrating away much faster than was expected.
    Experts believe that if Saturn's moons actually formed 4.5 billion
    years ago, soon after the birth of the Solar System, their
    current distances from the planet should be greater. Thus, the new
    research implies that the moons are younger than 4.5 billion years,
    favouring a theory that the moons formed from Saturn's rings. The
    team also found that the moon Rhea is moving away 10 times faster
    than the other moons, which is the first evidence that a planet's
    dissipation factor can vary with its distance in relation to the moon.
    The scientists have no good explanation; what is believed about the
    history of Saturn's moons might still change in the coming years with
    the conclusion of the Cassini mission.


    The Cassini space probe was launched in 1997 and arrived at Saturn in
    2004 July. Since then it has been in orbit around the planet and has
    sent back a stream of images of the surface as well as of the moons.
    Its principal discoveries have included the observation that Enceladus
    is spewing water into space from a sub-surface ocean, and that Titan
    is a strange Earth-like world where lakes and seas are fed by rivers
    and rain — except that it is frightfully cold, and the liquid is not
    water but is a mixture of hydrocarbons such as methane.
    Having spent 12 years orbiting around Saturn and seeing its moons at a
    relatively safe distance, the Cassini probe is now about to undertake
    a series of dare-devil manoeuvres. They will make the satellite dive
    repeatedly extremely close to – and through – the rings over the next
    nine months. The manoeuvres will culminate in Cassini ditching itself
    in Saturn's atmosphere. That destructive ending is necessary because
    the spacecraft is running low on fuel. NASA, which leads the Cassini
    mission, wants to make sure that an out-of-control probe does not at
    some future date crash into any of Saturn's moons – in particular,
    Enceladus and Titan. There is a chance that those moons harbour life,
    and a colliding satellite could introduce contamination from the
    Earth. That must not be allowed to happen. But in the lead-up to its
    safe disposal – set for September 15 next year – Cassini should gather
    some remarkable science. Starting on Wednesday, Cassini will repeat-
    edly climb high above Saturn's north pole and then plunge to a point
    just outside the F ring (the outer boundary of the main ring system).
    The probe will do 20 such orbits, even sampling some of the particles
    and gases associated with the F ring. Then, starting on April 22
    next year, Cassini will initiate a series of dives that will take it
    between the inner edge of the rings and the planet's atmosphere. On
    occasion, it could pass less than 2,000 km above Saturn's cloud tops.
    As well as returning some spectacular imagery of the rings and of
    moonlets previously seen only from a great distance, the upcoming
    manoeuvres are designed to permit investigation of Saturn's interior.

    Monash University

    Scientists find that new computer models and evidence from meteorites
    show that a low-mass supernova triggered the formation of the Solar
    System. About 4.6 billion years ago, a cloud of gas and dust that
    eventually formed the Solar System was disturbed. The ensuing
    gravitational collapse formed the proto-Sun with a surrounding disc
    where the planets were born. A supernova would have enough energy to
    induce the collapse of such a gas cloud. The research team decided to
    focus on short-lived radioactive nuclei that were present only in the
    early Solar System. Owing to their short lifetimes, those nuclei
    could have come only from the triggering supernova. Their abundances
    in the early Solar System have been inferred from their decay products
    in meteorites. As the debris from the formation of the Solar System,
    meteorites are comparable to the leftover bricks and mortar in a
    construction site. They tell us what the system is made of and, in
    particular, what short-lived nuclei the triggering supernova provided.
    Identification of those 'fingerprints' of the supernova is what was
    needed for an understanding of how the formation of the Solar System
    was initiated. The fingerprints point uniquely to a low-mass super-
    nova as the trigger. In addition to explaining the abundance of
    beryllium-10, the low-mass-supernova model would also explain the
    short-lived nuclei calcium-41, palladium-107, and a few other isotopes
    found in meteorites.


    In 2015, the All-Sky Automated Survey for SuperNovae (ASAS-SN)
    detected an event, named ASASSN-15lh, that was recorded as the
    brightest supernova ever seen, and categorised as a superluminous
    supernova — the explosion of an extremely massive star at the end of
    its 'life'. It was twice as bright as the previous record-holder, and
    at its peak was 20 times brighter than the total light output of the
    entire Milky Way. An international team has now made additional
    observations of the distant galaxy, about 4 billion light-years away,
    where the explosion took place and they have proposed a new explanation
    for this extraordinary event. The source was observed for 10 months
    following the event and it has been concluded that the explanation is
    unlikely to lie with an extraordinarily bright supernova. The results indicate
    that the event was probably caused by a rapidly spinning super-massive
    black hole as it destroyed a low-mass star. In that scenario, the
    extreme gravitational forces of a supermassive black hole, located in
    the centre of the host galaxy, ripped apart a Sun-like star that came
    too close — a so-called tidal disruption event, something so far only
    observed about 10 times. In the process, the star was 'spaghettified',
    and shocks in the colliding debris as well as heat generated in
    accretion led to a burst of light. That gave the event the appearance
    of a very bright supernova explosion, even though the star would not
    have become a supernova on its own as it did not have enough mass.
    The team based its new conclusions on observations from a selection of
    telescopes, both on the ground and in space. Among them was the Very
    Large Telescope at the Paranal Observatory, the New Technology Tele-
    scope at La Silla, and the Hubble Space Telescope. The observations
    with the NTT were made as part of the Public ESO Spectroscopic Survey
    of Transient Objects (PESSTO).
    There are several independent aspects of the observations that suggest
    that the event was indeed a tidal disruption and not a super-luminous
    supernova. In particular, the data showed that the event went through
    three distinct phases over the 10 months of follow-up observations.
    Overall, those data resemble more closely what would be expected for a
    tidal disruption rather than a supernova. An observed re-brightening
    in ultraviolet light, as well as a temperature increase, further
    reduce the likelihood of a supernova event. Furthermore, the location
    of the event, in a red, massive and passive galaxy, would be unusual
    for a super-luminous supernova explosion; such events normally occur
    in blue, star-forming dwarf galaxies. Although the team says that a
    supernova source is therefore very unlikely, it accepts that a
    classical tidal-disruption event would not be an adequate explanation
    for the event either. The tidal-disruption event proposed cannot be
    explained with a non-spinning super-massive black hole. The team
    argues that ASASSN-15lh was a tidal-disruption event arising from a
    very particular kind of black hole. The mass of the host galaxy
    implies that the black hole at its centre has a mass of at least 100
    million times that of the Sun. A black hole of such a mass would
    normally be unable to disrupt stars outside its event horizon — the
    boundary within which nothing is able to escape its gravitational
    pull. However, if the black hole is a particular kind that happens to
    be rapidly spinning — a so-called Kerr black hole — the situation
    changes and that limit no longer applies.

    University of Notre Dame

    Astronomers have identified what they believe to be the second
    generation of stars, shedding light on the nature of the Universe's
    first stars. A sub-class of carbon-enhanced metal-poor (CEMP) stars,
    the so-called CEMP-no stars, are ancient stars that have large amounts
    of carbon but little of the heavy metals (such as iron) common to
    later-generation stars. Massive first-generation stars made up of
    pure hydrogen and helium produced and ejected heavier elements by
    stellar winds during their lifetimes or when they exploded as super-
    novae. Those metals — anything heavier than helium, in astronomical
    parlance — polluted the nearby gas clouds from which new stars
    formed. The team has shown that the lowest-metallicity stars, the
    most chemically primitive, include large fractions of CEMP stars.
    The CEMP-no stars, which are also rich in nitrogen and oxygen, are
    probably the stars born out of hydrogen and helium gas clouds that
    were polluted by the elements produced by the Universe's first stars.
    The CEMP-no stars we see today, or at least many of them, were born
    shortly after the Big Bang, 13.5 billion years ago, out of almost
    completely unpolluted material. Those stars, located in the halo of
    our Galaxy, are true second-generation stars, born out of the nucleo-
    synthesis products of the very first stars.
    It is unlikely that any of the Universe's first stars still exist,
    but much can be learned about them from detailed studies of the next
    generation of stars. Astronomers are analyzing the chemical products
    of the very first stars by looking at what was locked up by the
    second-generation stars. They can use that information to tell the
    story of how the first elements were formed, and determine the
    distribution of the masses of those first stars. If we know how their
    masses were distributed, we can model the process of how the first
    stars formed and evolved from the very beginning. The authors used
    high-resolution spectroscopic data gathered by many astronomers to
    measure the chemical compositions of about 300 stars in the halo of
    the Milky Way. More and heavier elements form as later generations of
    stars continue to contribute additional metals. As new generations of
    stars are born, they incorporate the metals produced by the earlier
    generations. Hence, the more heavy metals a star contains, the more
    recently it was born. Our Sun, for example, is relatively young, with
    an age of only 4.5 billion years.


    Analysis of a great new galaxy survey, made with ESO's VLT Survey
    Telescope in Chile, suggests that dark matter may be less dense and
    more smoothly distributed throughout space than has previously been
    thought. An international team used data from the Kilo Degree Survey
    (KiDS) to study how the light from about 15 million distant galaxies
    was affected by the gravitational influence of matter on the largest
    scales in the Universe. The results appear to be in disagreement with
    earlier findings from the Planck satellite. For their analysis,
    researchers used survey images that covered five patches of the sky
    covering a total area of about 2200 times the size of the Full Moon
    and containing around 15 million galaxies. They were able to carry
    out one of the most precise measurements ever made of an effect known
    as cosmic shear — a subtle variant of weak gravitational lensing, in
    which the light emitted from distant galaxies is slightly warped by
    the gravitational effect of large amounts of matter, such as galaxy
    clusters. In cosmic shear, it is not galaxy clusters but large-scale
    structures in the Universe that warp the light — they produce an even
    smaller effect. Very wide and deep surveys, such as KiDS, are needed
    to ensure that the very weak cosmic-shear signal is strong enough to
    be measured and can be used by astronomers to map the distribution of
    gravitating matter. The presently described study relates to the
    largest area of the sky ever to be mapped with that technique so far.
    Intriguingly, the results of the analysis appear to be inconsistent
    with deductions from the results of ESA's Planck satellite, the
    leading space mission probing the fundamental properties of the
    Universe. In particular, the KiDS team's measurement of how clumpy
    matter is throughout the Universe — a key cosmological parameter —
    is significantly lower than the value derived from the Planck data.
    This latest result indicates that dark matter in the cosmic web, which
    accounts for about one-quarter of the content of the Universe, is less
    clumpy than we previously believed. Despite making up about 85% of
    the matter in the Universe, dark matter remains elusive, and rather
    than being detected directly, its presence is only inferred from its
    gravitational effects. Studies like these are the best current way to
    determine the shape, scale and distribution of the invisible material.
    The surprise result of this study also has implications for our wider
    understanding of the Universe, and how it has evolved during its
    almost-14-billion-year history. Such an apparent disagreement with
    previously established results from Planck means that astronomers may
    now need to re-formulate their understanding of some fundamental
    aspects of the development of the Universe. The findings will help to
    refine our theoretical models of how the Universe has grown from its
    inception up to the present day. The KiDS analysis of data from the
    VST is an important step, but future telescopes are expected to make
    even wider and deeper surveys of the sky. Unravelling what has
    happened since the Big Bang is a complex challenge, but by continuing
    to study the distant skies, we can build a picture of how our modern
    Universe has evolved. We see an intriguing discrepancy with Planck
    cosmology at the moment. Future missions such as the Euclid satellite
    and the Large Synoptic Survey Telescope will allow us to repeat these
    measurements and perhaps understand better what the Universe is really
    telling us.


    By studying with the VLT the light emitted from an extraordinarily
    dense and strongly magnetized neutron star, astronomers may have found
    the first observational indications of a strange quantum effect, first
    predicted in the 1930s. The polarisation of the observed light
    suggests that the empty space around the neutron star is subject to a
    quantum effect known as vacuum birefringence. Astronomers used the
    Very Large Telescope (VLT) at the Paranal Observatory in Chile to
    observe the neutron star RX J1856.5-3754, about 400 light-years away.
    Despite being amongst the closest neutron stars, its extreme dimness
    meant that the astronomers could only observe the star in visible
    light with the FORS2 instrument on the VLT, at the limits of current
    telescope technology. Neutron stars are the very dense remnant cores
    of massive stars (at least 10 times the mass of the Sun) that have
    exploded as supernovae at the ends of their 'lives'. They also have
    extreme magnetic fields, billions of times stronger than that of the
    Sun, which permeate their outer surfaces and surroundings. The fields
    are so strong that they even affect the properties of the empty space
    around the star. Normally a vacuum is thought of as being completely
    empty, and light can travel through it without being changed. But in
    quantum electrodynamics (QED), the quantum theory describing the
    interaction between photons and charged particles such as electrons,
    space is full of virtual particles that appear and vanish all the
    time. Very strong magnetic fields can modify the space so that it
    affects the polarization of light passing through it.

    According to QED, a highly magnetized vacuum behaves as a prism for
    the propagation of light, an effect known as vacuum birefringence.
    Among the many predictions of QED, however, vacuum birefringence so
    far lacked a direct experimental demonstration. Attempts to detect it
    in the laboratory have not yet succeeded in the 80 years since it was
    predicted in a paper by Werner Heisenberg (of uncertainty-principle
    fame) and Hans Heinrich Euler. The effect can be detected only in the
    presence of enormously strong magnetic fields, such as those around
    neutron stars. After careful analysis of the VLT data, the team
    detected linear polarization, at a significant level of around 16%,
    that they say is most probably due to the boosting effect of vacuum
    birefringence occurring in the area of empty space surrounding
    RX J1856.5-3754. That is the faintest object for which polarization
    has ever been measured. The high linear polarization measured with
    the VLT can not easily be explained by models unless the vacuum
    birefringence effects predicted by QED are included. Further improve-
    ments to this area of study could come about with more advanced
    telescopes. Polarization measurements with the next generation of
    telescopes, such as ESO's E-ELT, could play a crucial role in testing
    QED predictions of vacuum birefringence effects around many more
    neutron stars. The presently described measurement, made for the
    first time now in visible light, also paves the way to similar
    measurements to be carried out at X-ray wavelengths.


    Four more elements have officially been added to the seventh row of
    the Periodic Table. They are 113 nihonium (Nh), 115 moscovium (Mc),
    117 tennessine (Ts), and 118 oganesson (Og). There have been mentions
    of those four new elements since January, but the International Union
    of Pure and Applied Chemistry (IUPAC) has finally announced that the
    names have been officially approved. In keeping with tradition, the
    new elements have been named after a place or geographical region, or
    else a scientist. The endings of the names also reflect and maintain
    historical and chemical consistency: '-ium' for elements 113 and 115,
    as for all new elements of groups 1 to 16, '-ine' for element 117 and
    belonging to group 17 and '-on' for element 118 belonging to group 18.
    Nihonium is derived from Nihon, a Japanese word for Japan, and mosco-
    vium honours the Russian capital city, Moscow. Tennessine is named
    after the U.S. state of Tennessee, known for its pioneering research
    in chemistry. It is the second state to be honoured in the periodic
    table; the first was California, referenced by californium (element
    98). Oganesson is named after the 83-year-old Russian physicist Yuri
    Oganessian. This is only the second time that a new element has been
    named after a living scientist.

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

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