The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 431 Oct 9th

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    The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 431 2016 October 9

    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


    Astronomers using the Hubble space telescope have imaged what may be
    water-vapour plumes erupting from the surface of Jupiter's moon
    Europa. That finding bolsters other Hubble observations suggesting
    that the icy moon erupts with high-altitude water-vapour plumes. The
    observation increases the possibility that missions to Europa may be
    able to sample Europa's ocean without having to drill through miles of
    ice. The plumes are estimated to rise about 200 km before,
    presumably, raining material back down onto the surface. Europa
    has a huge global ocean containing twice as much water as the Earth's
    oceans, but it is protected by a layer of extremely cold and hard ice
    of unknown thickness. The original goal of the team's observing
    proposal was to determine whether Europa has a thin, extended
    atmosphere, or exosphere. Using the same observing method that
    detects atmospheres around planets orbiting other stars, the team
    realized that, if there were water vapour venting from Europa's
    surface, such an observation would be an excellent way to see it.
    The atmosphere of an extra-solar planet blocks some of any light that
    comes from behind it. If there is a thin atmosphere around Europa,
    then when Europa transits in front of Jupiter it could block some of
    the light of Jupiter, and we could see it as a silhouette. So
    astronomers were looking for absorption features around the limb of
    Europa as it transited the smooth face of Jupiter. In 10 separate
    occurrences spanning 15 months, the team observed Europa passing in
    front of Jupiter. It saw what could be plumes erupting on three of
    those occasions. In 2012, another team detected evidence of water
    vapour erupting from the frigid south-polar region of Europa and
    reaching more than 160 km into space. Although both teams used
    Hubble's 'Space Telescope Imaging Spectrograph' instrument, they used
    totally independent methods and arrived at the same conclusion. If
    confirmed, Europa would be the second moon in the Solar System known
    to have water-vapour plumes. In 2005, the Cassini orbiter detected
    jets of water vapour and dust spewing off the surface of Saturn's moon
    Enceladus. Scientists may use the infrared vision of the James Webb
    space telescope, which is scheduled to be launched in 2018, to confirm
    venting or plume activity on Europa.


    A team of astronomers using the Pan-STARRS 1 (PS1) survey has detected
    five new so-called 'Neptune trojans' — minor bodies sharing the same
    orbit as the planet Neptune. The PS1 survey, which utilizes the first
    Pan-STARRS (Panoramic Survey Telescope and Rapid Response System)
    telescope in Hawaii, offers one of the best ways to search for Neptune
    trojans. The survey, lasting from 2010 May to 2014 May, has made a
    strong contribution to knowledge of the Solar System's minor bodies
    owing to its very wide survey area and its optimized cadence for
    finding moving objects. The researchers found four new L4 trojans,
    meaning that they orbit Neptune's L4 Lagrangian point 60 degrees ahead
    of te planet; they also found one L5 trojan (orbiting the L5 region
    60 degrees behind it). The newly detected objects have sizes ranging
    from 100 to 200 km in diameter. The new L5 trojan is dynamically more
    unstable than the other four, indicating that it is probably only
    temporarily captured into the Neptune trojan cloud. Orbital
    simulations show that it librates stably only for several million
    years. That suggests that it must be of recent capture origin. On
    the other hand, all four new L4 trojans have stably occupied the 1:1
    resonance with Neptune for more than 1 billion years. They may,
    therefore, be of primordial origin. The team also found that there
    seem to be two groups of Neptune trojans: one group with orbital
    inclinations less than 10°, and the other with inclinations more than
    18°. There is none with intermediate inclinations — the trojan
    population has a bimodal inclination distribution, but the small
    numbers involved do not make for high statistical certainty.

    Carnegie Institution for Science

    When a star is young, it is often still surrounded by a primordial
    rotating disc of gas and dust, from which planets can form. Astrono-
    mers like to find such discs because they might be able to observe the
    star part-way through the planet-formation process, but it is highly
    unusual to find such discs around brown dwarfs or stars with very low
    masses. Canadian astronomers have discovered four new low-mass
    objects surrounded by discs. Three of the four objects are quite
    small, between only 13 and 18 times the mass of Jupiter. The fourth
    has about 120 times Jupiter's mass. (For comparison, the Sun is just
    over 1,000 times more massive than Jupiter.) In a planet-forming
    disc, the dust grains collide and aggregate to form pebbles, which
    grow into boulders, and so on, increasing in size through planetes-
    imals, planetary embryos, and finally rocky terrestrial planets (some
    of which then become the cores for gas-giant planets). Astronomers
    are able to identify those types of planet-birthing discs, because the
    star heats up the surrounding dust, which affects the way it looks in
    infrared light. However, some discs indicate that planet formation is
    not ongoing, but has already finished. Those ones are made up of the
    debris left behind by all the collisions during planet formation and
    by subsequent collisions of the newly formed planets. Eventually
    those dusty remains are swept away. But until that happens, a cooler,
    thinner ring of dust surrounds the star. Some discs even represent an
    intermediate stage between the planet-forming and dusty-remnant
    phases. It is important for astronomers to try to distinguish between
    those different types of discs, because then they can chart better the
    way that planetary systems, including our own Solar System, are born
    and change over time. The research team was able to determine that
    the discs surrounding their four newly discovered low-mass objects
    were all likely to be in a phase of planet-forming; none was in the
    dusty-aftermath phase. Even more interesting, two of the objects are
    possibly between 42 and 45 million years old. That would make them
    the oldest objects surrounded by active disc systems ever found.


    An international team using ALMA, along with the Very Large Telescope
    and other telescopes, has discovered the true nature of a rare object
    in the distant Universe called a Lyman-alpha Blob. Up till now
    astronomers did not understand what made those huge clouds of gas
    shine so brightly, but ALMA has now seen two galaxies at the heart of
    one of those objects and they are undergoing a frenzy of star
    formation that is lighting up their surroundings. Those large
    galaxies are in turn at the centre of a swarm of smaller ones in what
    appears to be an early phase in the formation of a massive cluster of
    galaxies. The two ALMA sources are expected to evolve into a single
    giant elliptical galaxy. Lyman-alpha Blobs (LABs) are gigantic clouds
    of hydrogen gas that can span hundreds of thousands of light-years and
    are found at very large cosmic distances. The name reflects the
    characteristic wavelength of ultraviolet light that they emit, known
    as Lyman-alpha radiation. Since their discovery, the processes that
    give rise to LABs have been an astronomical puzzle. But new
    observations with ALMA may now have now cleared up the mystery. One
    of the largest Lyman-alpha Blobs known, and the most thoroughly
    studied, is SSA22-Lyman-alpha Blob 1, or LAB-1. Embedded in the core
    of a huge cluster of galaxies in the early stages of formation, it was
    the very first such object to be discovered, in 2000, and is located
    so far away that its light has taken about 11.5 billion years to
    reach us.
    A team of astronomers has now used the Atacama Large Millimetre/
    Sub-millimetre Array (ALMA) to observe light from cool dust clouds in
    distant galaxies to look deeply into LAB-1. That allowed it to
    pinpoint and resolve several sources of sub-millimetre emission. It
    then combined the ALMA images with observations from the Multi-Unit
    Spectroscopic Explorer (MUSE) instrument mounted on ESO's Very Large
    Telescope (VLT), which map the Lyman-alpha light. That showed that
    the ALMA sources are located in the very heart of the Lyman-alpha
    Blob, where they are forming stars at a rate over 100 times that of
    the Milky Way. Deep imaging with the Hubble space telescope and
    spectroscopy at the Keck Observatory showed in addition that the ALMA
    sources are surrounded by numerous faint companion galaxies that could
    be bombarding the central ALMA sources with material, helping to drive
    their high star-formation rates. The team then turned to a
    sophisticated simulation of galaxy formation to demonstrate that the
    giant glowing cloud of Lyman-alpha emission can be explained if
    ultraviolet light produced by star formation in the ALMA sources
    scatters off the surrounding hydrogen gas. That would give rise to
    the Lyman-alpha Blob that we see. Understanding how galaxies form and
    evolve is a massive challenge. Astronomers think Lyman-alpha Blobs
    are important because they seem to be the places where the most
    massive galaxies in the Universe form. In particular, the extended
    Lyman-alpha glow provides information on what is happening in the
    primordial gas clouds surrounding young galaxies, regions that are
    very difficult to study, but critical to our understanding.


    Japanese researchers have used ALMA to observe a massive star known as
    ST11 in our neighbouring dwarf galaxy, the Large Magellanic Cloud
    (LMC). Emission from a number of molecular gases was detected.
    It indicated that the team had discovered a concentrated region of
    comparatively hot and dense molecular gas around the newly ignited
    star ST11. That was evidence that they had found something never
    before seen outside the Milky Way — a hot molecular core. The ALMA
    observations revealed that the newly discovered core in the LMC has a
    composition very different from that of otherwise similar objects in
    the Milky Way. The most prominent chemical signatures in the LMC core
    include familiar molecules such as sulphur dioxide, nitric oxide, and
    formaldehyde, alongside the ubiquitous dust. But several organic
    compounds, including methanol (the simplest alcohol molecule), had
    remarkably low abundances in the newly detected hot molecular core.
    In contrast, cores in the Milky Way have been observed to contain a
    wide assortment of complex organic molecules, including methanol and
    ethanol. The LMC has a low abundance of elements other than hydrogen
    and helium. The research team suggests that that very different
    galactic environment has affected the molecule-forming processes
    taking place surrounding the newborn star ST11. That could account
    for the observed differences in chemical compositions. It is not yet
    clear if the large, complex molecules detected in the Milky Way exist
    in hot molecular cores in other galaxies. Complex organic molecules
    are of very special interest because some are connected to prebiotic
    molecules formed in space. The newly discovered object in one of our
    nearest galactic neighbours is an excellent object to help astronomers
    address that issue. It might also raise a hypothetical question: how
    could the chemical diversity of galaxies affect the development of
    extragalactic life?


    Scientists using the Fermi gamma-ray space telescope have found the
    first gamma-ray binary in another galaxy and the most luminous one
    ever seen. The dual-star system, dubbed LMC P3, contains a massive
    star and a crushed stellar core that interact to produce a cyclic
    flood of gamma rays, the highest-energy form of light. Fermi has
    detected only five such systems in our own galaxy, so finding one so
    luminous and distant is quite exciting. Gamma-ray binaries are prized
    because the gamma-ray output changes significantly during each orbit
    and sometimes over longer time-scales. The variation lets us study in
    detail many of the emission processes common to other gamma-ray
    sources. Those rare systems contain either a neutron star or a black
    hole, and radiate most of their energy in the form of gamma rays.
    Remarkably, LMC P3 is the most luminous such system known in gamma
    rays, X-rays, radio waves and visible light, and it is only the second
    one discovered with Fermi. LMC P3 lies within the expanding debris of
    a supernova explosion located in the Large Magellanic Cloud (LMC). In
    2012, scientists using the Chandra X-ray observatory found a strong
    X-ray source within the supernova remnant and showed that it was
    orbiting a hot, young star many times the Sun's mass. The researchers
    concluded that the compact object was either a neutron star or a black
    hole, and classified the system as a high-mass X-ray binary (HMXB).
    In 2015, the team began looking for new gamma-ray binaries in Fermi
    data by searching for the periodic changes characteristic of such
    systems. The scientists discovered a 10.3-day cyclic change centred
    near one of several gamma-ray point sources recently identified in the
    LMC. One of them, called P3, was not linked to objects seen at any
    other wavelengths but was located near the HMXB. The question arose,
    were they the same object?
    To find out, astronomers observed the binary in X-rays with the Swift
    satellite, at radio wavelengths with the Australia Telescope Compact
    Array near Narrabri, and in visible light with the 4.1-m Southern
    Astrophysical Research Telescope in Chile and the 1.9-m telescope at
    the SAAO in South Africa. The Swift observations clearly revealed the
    same 10.3-day emission cycle seen in gamma rays by Fermi. They also
    indicated that the brightest X-ray emission occurs opposite to the
    gamma-ray peak, so when one reaches maximum the other is at minimum.
    Radio data exhibit the same period and out-of-phase relationship with
    the gamma-ray peak, confirming that LMC P3 is indeed the same system
    investigated by Chandra. The optical observations show changes due to
    binary orbital motion, but because scientists do not know how the
    orbit is tilted with respect to our line of sight, they can only
    estimate the individual masses. The star is between 25 and 40 times
    the Sun's mass, and if we are viewing the system at an angle midway
    between face-on and edge-on, which seems most likely, its companion is
    a neutron star about twice the Sun's mass. If, however, we view the
    binary nearly face-on, then the companion must be significantly more
    massive and must be a black hole.
    In gamma-ray binaries, the compact companion is thought to produce a
    'wind' of its own, one consisting of electrons accelerated to near the
    speed of light. The interacting outflows produce X-rays and radio
    waves throughout the orbit, but those emissions are detected most
    strongly when the compact companion travels along the part of its
    orbit closest to the Earth. Through a different mechanism, the
    electron wind also emits gamma rays. When light from the star
    collides with high-energy electrons, it receives a boost to gamma-ray
    levels. Called inverse-Compton scattering, that process produces more
    gamma rays when the compact companion passes near the star on the far
    side of its orbit as seen from our perspective. Before Fermi was
    launch, gamma-ray binaries were expected to be more numerous than they
    have turned out to be. Hundreds of HMXBs are catalogued, and those
    systems are thought to have originated as gamma-ray binaries following
    the supernova that formed the compact object. It is certainly a
    surprise to detect a gamma-ray binary in another galaxy before we find
    more of them in our own. One possibility is that the gamma-ray
    binaries that Fermi has found are rare cases where a supernova formed
    a neutron star with an exceptionally rapid spin, which would enhance
    how it produces accelerated particles and gamma rays.

    Science Daily

    China's first-ever space lab will burn up in the Earth's atmosphere
    towards the end of next year. The 8.5-ton Tiangong-1 spacecraft is
    currently intact and orbiting the Earth at an altitude of 370 km,
    which is a bit lower than the International Space Station, which
    usually stays about 400 km up. Tiangong-1 will probably fall back to
    Earth in the second half of 2017, but its demise should not cause
    problems here on the ground. China is monitoring Tiangong-1 (whose
    name means 'Heavenly Palace' in Mandarin) closely, and will issue
    appropriate warnings if the space lab threatens to hit a satellite.
    China will release a forecast of Tiangong-1's fall to Earth 'if
    necessary'. The update seems to confirm speculation that China is no
    longer in control of the 10.3-m space lab which was launched in 2011
    September to test docking technologies and other skills that China
    will need to build its planned space station in the early 2020s.
    After all, if operators were still controlling the space lab, they
    could steer it to a guided re-entry over an empty stretch of ocean at
    a specified time. Two astronauts are scheduled to arrive at
    Tiangong-2 in mid- to late October for a 30-day stay. The Shenzhou-9
    and Shenzhou-10 crews spent eight and 12 days aboard Tiangong-1,
    respectively. China is not part of the multi-national consortium,
    led by the United States and Russia, that operates the 400-ton
    International Space Station. China aims to have its own 54-ton space
    station in Earth orbit by 2022 or so.

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