The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 427 August 14th

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    The SOCIETY for POPULAR ASTRONOMY
    Electronic News Bulletin No. 427 2016 August 14

    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/

    CASSINI FINDS FLOODED CANYONS ON TITAN
    NASA

    The Cassini spacecraft has found, on Saturn's large moon Titan, deep,
    steep-sided canyons that are flooded with liquid hydrocarbons. The
    finding represents the first direct evidence of the presence of liquid-
    filled channels on Titan, as well as the first observation of canyons
    hundreds of metres deep. The Cassini observations reveal that the
    channels — in particular, a network of them named Vid Flumina — are
    narrow canyons, generally a bit less than a kilometre wide, with slopes
    steeper than 40 degrees. The canyons also are quite deep — those
    measured are 240 to 570 metres from top to bottom. The branching
    channels appear dark in radar images, much like Titan's methane-rich
    seas. That suggested to scientists that the channels might also be
    filled with liquid, but a direct detection had not been made until now.
    Previously it was not clear if the dark material was liquid or merely
    saturated sediment — which at Titan's frigid temperatures would be made
    of ice, not rock. Cassini's radar is often used as an imager, providing
    a window to see through the dense haze that surrounds Titan to reveal the
    surface below. But during a recent pass, the radar was used as an
    altimeter, sending pings of radio waves to the moon's surface to measure
    the height of features there. The researchers combined the altimetry
    data with previous radar images of the region to make their discovery.
    The key to understanding the nature of the channels was the way Cassini's
    radar signal reflected off the bottoms of the features. The radar
    instrument observed a glint, indicating an extremely smooth surface like
    that observed from Titan's hydrocarbon seas. The timing of the radar
    echoes, as they bounced off the canyons' edges and floors, provided
    direct measures of their depths. The presence of such deep cuts in the
    landscape indicates that whatever process created them was active for a
    long time or eroded down much faster than in other areas of Titan's
    surface. The researchers' proposed scenarios include uplift of the
    'terrain' and changes in sea level, probably both. It is likely that a
    combination of those processes led to the formation of the deep canyons,
    but it is not clear to what degree each was involved. What is clear is
    that any description of Titan's evolution needs to be able to explain how
    the canyons got there. Terrestrial examples of both of those types of
    canyon-carving processes are found along the Colorado River in Arizona.
    An example of uplift powering erosion is the Grand Canyon, where the
    terrain's rising altitude caused the river to cut deeply downward into
    the landscape over the course of several million years. For canyon
    formation driven by variations in water level, look to Lake Powell. When
    the water level in the reservoir drops, it increases the river's rate of
    erosion. While the altimeter data also showed that the liquid in some of
    the canyons around Ligeia Mare is at sea level — the same altitude as
    the liquid in the sea itself — in others it sits tens of metres higher
    in elevation. The researchers interpret the latter to be tributaries
    that drain into the main channels below. Future work will extend the
    methods used in this study to all the other channels that Cassini's radar
    altimeter has observed on Titan. The researchers expect their continued
    work to produce a more comprehensive understanding of forces that have
    shaped Titan's landscape.

    NEW DISTANT DWARF PLANET BEYOND NEPTUNE
    University of British Columbia

    Astronomers have discovered a new dwarf planet orbiting in the disc of
    small icy bodies beyond Neptune. The new object is about 700 km in
    diameter and has one of the largest orbits for a dwarf planet.
    Designated 2015 RR245 by the International Astronomical Union's Minor
    Planet Center, it was found with the Canada-France-Hawaii Telescope on
    Mauna Kea, Hawaii, as part of the ongoing 'Outer Solar System Origins
    Survey' (OSSOS). The OSSOS project uses computers to hunt for the
    images, and the team was presented with a bright object moving at such a
    slow rate that it was clearly at least 120 times further from the Sun
    than the Earth. The size of RR245 is not yet exactly known, as its
    surface properties need further measurement. The vast majority of dwarf
    planets like RR245 were destroyed or thrown from the Solar System as the
    giant planets moved out to their present positions. RR245 is one of the
    few that survived to the present day, along with Pluto and Eris, the
    largest known dwarf planets. RR245 now circles the Sun among the remnant
    population of tens of thousands of much smaller trans-Neptunian bodies,
    most of which orbit unseen. RR245 has been on its highly eccentric orbit
    for at least the last 100 million years. After hundreds of years further
    than 80 astronomical units (AU) from the Sun, RR245 is travelling towards
    its closest approach at five billion km (34 AU), which it will reach
    around 2096. As RR245 has been observed for only one of the 700 years it
    takes to orbit the Sun, where it came from and how its orbit will slowly
    evolve in the far future is unknown. Its precise orbit will be refined
    over the coming years, after which RR245 will be given a name. As
    discoverers, the OSSOS team can submit their preferred name for RR245 to
    the International Astronomical Union for consideration. RR245 is the
    largest discovery and the only dwarf planet found by OSSOS, which has
    discovered more than five hundred new trans-Neptunian objects.

    FAINTEST HISSES REVEAL FAMOUS STAR'S PAST LIFE
    RAS
    Astronomers have managed to see into the past of a nearby star millions
    of years before its famous explosion, using a telescope in remote outback
    Australia at a site free from FM radio interference. Astronomers
    observing the region at the lowest-ever radio frequencies have helped to
    improve our understanding of stellar explosions. The research paints a
    picture of the star's life long before its death in what was the closest
    and brightest supernova yet seen, now known as supernova remnant 1987A
    (SN 1987A), which collapsed spectacularly almost 30 years ago in a
    neighbouring galaxy, the Large Magellanic Cloud. Much had been known
    about the immediate past of that star through study of the remnants
    resulting from the its collapse in 1987 However, it was the detection of
    the very faint hiss through low-frequency radio astronomy that has
    provided the latest insights. Previously, out of the dead star's multi-
    million-year life, only about 0.1%, or 20,000 years, had been observable.
    Operating the Murchison Widefield Array in the West Australian desert,
    the radio astronomers were able to 'see' right back to when the star was
    in its long-lasting red-supergiant phase.

    Previous studies focused on material that was ejected into space when the
    star was in its final blue-supergiant phase. Researchers found the red
    supergiant lost its matter at a slower rate and generated winds that
    pushed into its surrounding environment less quickly than was previously
    assumed. The new data improve our knowledge of the composition of space
    in the region of SN 1987A; we can now go back to our simulations and
    improve them, the better to reconstruct the physics of supernova explo-
    sions. The key to gaining the new insights was the quiet environment in
    which the radio telescope is located. Nobody knew what was happening at
    low radio frequencies, because the signals from our own Earthbound FM
    radio drown the faint signals from space. Now, by studying the strength
    of the radio signal, astronomers can for the first time calculate how
    dense the surrounding gas is, and thus understand the environment of the
    star before it died.

    GIANT STELLAR VOID IN MILKY WAY
    RAS

    A major revision is required in our understanding of our Milky Way
    Galaxy, according to a team of Japanese, South African and Italian
    astronomers who find that there is a huge region around the centre of the
    Galaxy which is devoid of young stars. The Milky Way is a spiral galaxy
    containing many thousand million stars, with our Sun about 26,000 light-
    years from its centre. Measuring the distribution of the stars is
    crucial to our understanding of how our Galaxy formed and evolved.
    Pulsating stars called Cepheids are ideal for that purpose. They are
    much younger (between 10 and 300 million years old) than our Sun (4,600
    million years old) and they pulsate in brightness in regular cycles. The
    length of the cycle is related to the luminosity of the Cepheid, so if
    astronomers monitor them they can establish how bright the star really
    is, compare it with how bright it looks from here, and work out its
    distance. Finding Cepheids in the inner Milky Way is difficult, however,
    as the Galaxy is full of interstellar dust which attenuates light and
    hides many stars from view. The team compensated for that, with an
    analysis of near-infrared observations made with a Japanese–South-
    African telescope located at Sutherland, South Africa. To their surprise
    they found hardly any Cepheids in a huge region stretching for thousands
    of light-years from the core of the Galaxy. Astronomers already found
    some time ago that there are Cepheids in the central heart of our Milky
    Way (in a region about 150 light-years in radius). Now we find that,
    outside that, there is a huge Cepheid desert extending out to 8000
    light-years from the centre. That suggests that a large part of the
    Galaxy, called the Extreme Inner Disc, has no young stars — a conclusion
    that is contrary to other recent work, but in line with the work of radio
    astronomers who see no new stars being born in that desert. Cepheids
    have more typically been used to measure the distances of objects in the
    distant Universe, and the new work is an example instead of the same
    technique revealing the structure of our own Milky Way.
    LIGO GRAVITATIONAL WAVES MAY HAVE ORIGINATED FROM PRIMORDIAL BLACK HOLES
    Kyoto University
    Binary black holes recently discovered by the LIGO–Virgo collaboration
    could be primordial entities that formed just after the Big Bang,
    according to a report by Japanese astrophysicists. If further data
    support that conclusion, it could mark the first confirmed finding of a
    primordial black hole, guiding theories about the beginnings of the
    Universe. In February, the Virgo collaboration announced the first
    successful detection of gravitational waves. The waves were created from
    a merger of two black holes thirty times the mass of the Sun. It is
    extremely rare for such massive black holes to form in the present-day
    Universe. After that announcement, many astrophysicists started
    considering how such massive black holes were created, and how such
    black-hole binaries were formed. As a starting point, the team
    hypothesized that primordial black holes — formed following the Big Bang
    — were distributed randomly in space. The Universe was extremely hot
    and dense when it was first born. Primordial black holes came into being
    when gravitational collapse happened in regions which were especially
    dense. They have a completely different origin from black holes that
    form from celestial bodies.
    The research team evaluated, on the basis of general relativity, how
    often black holes merge in the present epoch. They found that the
    LIGO–Virgo team's observational data on merger frequencies would fall in
    to place if the binaries were primordial, and if they constitute a
    thousandth of all dark matter in the Universe. Primordial black-hole
    binaries were discussed extensively in the 1990s; however, interest in
    them waned when observations implied that their number was limited. To
    date, no one has found any primordial black holes, possibly making the
    LIGO–Virgo observations the first of their kind. Theoretical models
    about the beginnings of the Universe are still hotly contested. Some
    models necessarily predict the existence of primordial black holes, so
    their discovery might offer important clues about the Universe's early
    days. When more observational data related to black-hole binaries have
    accumulated, it may become possible to decide whether they are truly
    primordial.

    Bulletin compiled by Clive Down
    [url=http://http://www.popastro.com]http://www.popastro.com[/url]

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