The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 457 2017 Nov 19

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    The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 457 2017 November 19
    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 [url=http://][/url]

    When the Mars Pathfinder touched down in 1997, it had five cameras: two
    on a mast that popped up from the lander, and three on NASA's first
    rover, Sojourner. Since then, camera technology has seen appreciable
    improvement. Photo-sensors that were improved by the space programme
    have become commercially ubiquitous. Cameras have shrunk in size,
    increased in quality and are now carried in every cellphone and laptop.
    That same evolution has returned to space. The Mars 2020 mission will
    have more 'eyes' than any rover before it — a grand total of 23, to
    create sweeping panoramas, reveal obstacles, study the atmosphere, and
    assist instruments. They will provide dramatic views during the rover's
    descent to Mars and be the first to capture images of a parachute as it
    opens in the atmosphere of another planet. There will even be a camera
    inside the rover's body, which will study samples as they are stored and
    left on the surface for collection by a future mission. They represent
    a steady progression since Pathfinder: after that mission, the Spirit
    and Opportunity rovers were designed with 10 cameras each, including on
    their landers; Mars Science Laboratory's Curiosity rover has 17. Camera
    technology keeps improving; each successive mission is able to utilize
    the improvements, with better performance and lower cost. The cameras
    on Mars 2020 will include more colour and 3-D imaging than on Curiosity.
    On the new rover, the engineering cameras have been upgraded to acquire
    high-resolution, 20-megapixel colour images.


    The ALMA Observatory in Chile has detected dust around the closest star
    to the Solar System, Proxima Centauri. The new observations reveal the
    glow coming from cold dust in a region from one to four times as far
    from Proxima Centauri as the Earth is from the Sun. The data also hint
    at the presence of an even cooler outer dust belt and may indicate the
    presence of an elaborate planetary system. Those structures are similar
    to the much larger belts in the Solar System, and are expected to be
    made from particles of rock and ice that failed to form planets.
    Proxima Centauri is the closest star to the Sun. It is a faint red
    dwarf lying just four light-years away in the southern constellation
    Centaurus. It is orbited by the Earth-sized temperate world Proxima b,
    discovered in 2016 and the closest planet to the Solar System. But
    there is more to this system than just a single planet. The new ALMA
    observations reveal emission from clouds of cold cosmic dust surrounding
    the star. The dust around Proxima is important because, following the
    discovery of the terrestrial-type planet Proxima b, it is the first
    indication of the presence of an elaborate planetary system, and not
    just a single planet, around the star closest to the Sun. Dust belts
    are the remains of material that did not form into larger bodies such as
    planets. The particles of rock and ice in the belts vary in size from a
    tiny dust grain, smaller than a millimetre across, up to asteroid-like
    bodies many kilometres in diameter.
    Dust appears to lie in a belt that extends a few hundred million kilo-
    metres from Proxima Centauri and has a total mass of about one hundredth
    of the Earth's mass. The belt is estimated to have a temperature of
    about -230 degrees Celsius, as cold as that of the Kuiper Belt in the
    outer Solar System. There are also hints in the ALMA data of another
    belt of even colder dust about ten times further out. If the outer belt
    is confirmed, its nature is intriguing, given its very cold environment
    far from a star that is cooler and fainter than the Sun. Both belts
    are much further from Proxima Centauri than the planet Proxima b, which
    orbits just four million kilometres from its parent star. That suggests
    that Proxima Centauri may have a multiple planet system with a rich
    history of interactions that resulted in the formation of a dust belt.
    Further study may also provide information that might point to the
    locations of as-yet-unidentified additional planets. Proxima Centauri's
    planetary system is also particularly interesting because there are
    plans — the Starshot project — for future direct exploration of the
    system with microprobes attached to laser-driven sails. A knowledge of
    the dust environment around the star would be needed for planning such a


    A team working with the High-Accuracy Radial-velocity Planet Searcher
    (HARPS) at the La Silla Observatory in Chile has found that the red
    dwarf star Ross 128 is orbited by a low-mass exoplanet every 9.9 days.
    That Earth-sized world is expected to be temperate, with a surface
    temperature that may also be close to that of the Earth. Ross 128 is
    the 'quietest' nearby star to host such a temperate exoplanet. Red
    dwarfs are some of the coolest, faintest — and most common — stars
    in the Universe. That makes them very good targets in the search for
    exoplanets, so they are increasingly being studied. In fact, it is
    easier to detect small cool analogues of the Earth around such stars
    than around stars more similar to the Sun. Many red dwarf stars,
    including Proxima Centauri, are subject to flares that occasionally
    bathe their orbiting planets in deadly ultraviolet and X-ray radiation.
    However, it seems that Ross 128 is a much quieter star, and so its
    planets may be the closest known comfortable abode for possible life.
    Although it is currently 11 light-years from the Earth, Ross 128 is
    moving towards us and is expected to become our nearest stellar
    neighbour in just 79 000 years — a blink of the eye in cosmic terms.
    Ross 128b will by then have taken the crown from Proxima b and become
    the closest exoplanet to the Earth.
    With the data from HARPS, the team found that Ross 128b orbits 20
    times closer to its star than the Earth orbits the Sun. Despite that
    proximity, Ross 128b receives only 1.38 times more radiation than the
    Earth. As a result, Ross 128b's equilibrium temperature is estimated
    to lie between -60 and 20C, thanks to the cool and faint nature of its
    small red-dwarf host star, which has just over half the surface
    temperature of the Sun. While the scientists involved in this discovery
    consider Ross 128b to be a temperate planet, uncertainty remains as to
    whether the planet lies inside, outside, or on the cusp of the habitable
    zone, where liquid water may exist on a planet's surface. Astronomers
    are now detecting more and more temperate exoplanets, and the next stage
    will be to study their atmospheres, composition and chemistry in more
    detail. Vitally, the detection of biomarkers such as oxygen in the very
    closest exoplanet atmospheres will be an important next step, which
    ESO's Extremely Large Telescope (ELT) is in the prime position to take.

    Chalmers University of Technology

    A team of astronomers has used the telescope ALMA (Atacama Large
    Millimetre/submillimetre Array) to make the sharpest observations yet
    of a star with the same initial mass as the Sun. The new images show
    for the first time details on the surface of the red giant W Hydrae,
    320 light-years distant in the constellation of Hydra. W Hydrae is
    an example of an AGB (asymptotic-giant-branch) star. Such stars are
    cool, bright, old, and lose mass via stellar winds. The name derives
    from their positions in the famous Hertzsprung-Russell diagram, which
    classifies stars according to their brightness and temperature. Stars
    like the Sun evolve over time-scales of thousands of millions of years.
    When they reach old age, they puff up and become bigger, cooler and more
    prone to lose mass in the form of stellar winds. Stars manufacture
    important elements like carbon and nitrogen. When they reach the red-
    giant stage, those elements are released into space, ready to be used in
    subsequent generations of new stars. ALMA's images provide the clearest
    view yet of the surface of a red giant with a mass similar to that of
    the Sun. Earlier sharp images have shown details on much more massive,
    red supergiant stars like Betelgeuse and Antares. The observations have
    also surprised the scientists. The presence of an unexpectedly compact
    and bright spot provides evidence that the star possesses surprisingly
    hot gas in a layer above its surface: a chromosphere. An alternative
    possibility is at least as surprising: that the star was undergoing a
    giant flare when the observations were made. The scientists are now
    carrying out new observations, both with ALMA and other instruments, in
    an effort to understand W Hydrae's surprising atmosphere.


    A giant planet, which should not exist according to planet-formation
    theory, has been discovered around a distant star. The existence of the
    'monster' planet, NGTS-1b, challenges theories of planet formation which
    state that a planet of that size could not be formed around such a small
    star. According to those theories, small stars can readily form rocky
    planets but do not gather enough material together to form Jupiter-sized
    planets. NGTS-1b however, is a 'gas giant' — owing to its size and
    temperature, it is known as a 'hot Jupiter', a class of planets that are
    at least as large as our Solar System's Jupiter, but with around 20%
    less mass. Unlike Jupiter, however, NGTS-1b is very close to its star
    — just 3% of the distance between the Earth and the Sun, and completes
    an orbit every 2.6 days, so a year on NGTS-1b lasts two and a half
    Earth-days. In contrast, the host star is small, with a radius and mass
    half that of our Sun. NGTS-1b is the first planet discovered by the
    Next-Generation Transit Survey (NGTS), which is being conducted at ESO's
    Paranal Observatory in the Atacama Desert in Chile and employs an array
    of 12 telescopes to scour the sky. The researchers made their discovery
    by continually monitoring patches of the night sky over many months, and
    detecting red light from the star with innovative red-sensitive cameras.
    They noticed dips in the light from the star every 2.6 days, implying
    that a planet was orbiting and periodically blocking the starlight.
    Using those data, they then tracked the planet's orbit and calculated
    the size, position and mass of NGTS-1b by measuring the radial velocity
    of the star. In fact, that method, measuring how much the star wobbles
    owing to the gravitational attraction of the planet, seemed the best way
    of measuring NGTS-1b's size.

    NASA/Goddard Space Flight Center

    Before its brief mission ended unexpectedly in 2016 March, Japan's
    Hitomi X-ray observatory captured exceptional information about the
    motions of hot gas in the Perseus galaxy cluster. Now, scientists have
    been able to analyze more deeply the chemical make-up of that gas,
    providing new insights into the stellar explosions that formed most of
    the elements and cast them into space. The Perseus cluster, located 240
    million light-years away in its namesake constellation, is the brightest
    galaxy cluster in X-rays and among the most massive ones that are 'near'
    the Earth. It contains thousands of galaxies orbiting within a thin hot
    gas, all bound together by gravity. The gas averages 50 million degrees
    Celsius and is the source of the cluster's X-ray emission. Using
    Hitomi's high-resolution Soft X-ray Spectrometer (SXS) instrument,
    researchers observed the cluster between 2016 Feb. 25 and March 6,
    acquiring a total exposure of nearly 3.4 days. The SXS observed an
    unprecedented spectrum, revealing a landscape of X-ray peaks emitted
    from various chemical elements with a resolution some 30 times better
    than had previously been achieved. The scientific team shows that the
    proportions of elements found in the cluster are nearly identical to
    the ones astronomers see in the Sun. There was no reason to expect that
    initially, since the Perseus cluster is a different environment with a
    different history from our Sun's. After all, clusters represent an
    average chemical distribution from many types of stars in many types of
    galaxies that formed long before the Sun. One group of elements is
    closely tied to a particular class of stellar explosion, called Type Ia
    supernovae. Those blasts are thought to be responsible for producing
    most of the Universe's chromium, manganese, iron and nickel — metals
    collectively known as 'iron-peak' elements. Type Ia supernovae entail
    the total destruction of a white dwarf, a compact remnant produced by
    stars like the Sun. Although stable on its own, a white dwarf can
    undergo a runaway thermonuclear explosion if it is paired with another
    object as part of a binary system. That occurs either by merging with a
    companion white dwarf or, when paired with a nearby normal star, by
    stealing some of its partner's gas. The transferred matter can accumu-
    late on the white dwarf, gradually increasing its mass until it becomes
    unstable and explodes.
    An important open question has been whether the exploding white dwarf is
    close to the stability limit — about 1.4 solar masses — regardless of
    its origins. Different masses produce different amounts of iron-peak
    metals, so a detailed tally of those elements over a large region of
    space, like the Perseus galaxy cluster, could indicate which kinds of
    white dwarfs blew up more often. It turns out that a combination of
    Type Ia supernovae, with different masses at the moments of their
    explosions, is needed to produce the chemical abundances that we see in
    the gas at the middle of the Perseus cluster. Astronomers can confirm
    that at least about half of Type Ia supernovae must have reached nearly
    1.4 solar masses. Taken together, the findings suggest that the same
    combination of Type Ia supernovae producing iron-peak elements in our
    Solar System also produced those elements in the cluster's gas. That
    means that the Solar System and the Perseus cluster experienced broadly
    similar chemical evolution, suggesting that the processes forming stars
    — and the systems that became Type Ia supernovae — were comparable in
    the two locations. Although this is just one example, there is no clear
    reason to doubt that such similarity could extend beyond our Sun and the
    Perseus cluster to other galaxies with different properties.

    University of Massachusetts at Amherst

    Astronomers using the Large Millimeter Telescope (LMT) have detected
    the second-most-distant dusty, star-forming galaxy ever found in the
    Universe — born in the first thousand million years after the Big Bang.
    It is the oldest object ever detected by the LMT, and at present there
    is only one other object like it known, a slightly older and more
    distant one. Seeing an object within the first thousand million years
    is remarkable, because the Universe was fully ionized, that is, it was
    too hot and too uniform to form anything for the first 400 million
    years. So our best guess is that the first stars and galaxies and black
    holes all formed within the first 500 to 1000 million years. The newly
    observed object is very close to being one of the first galaxies ever to
    form. This result is not a surprise, because it is what the LMT was
    built to do, but it excites astronomers. High-redshift, very-distant
    objects are a class of mythical beasts in astrophysics. Astronomers
    always knew that there were some out there that are enormously large and
    bright, but they are invisible in visible light because they are so
    obscured by the thick dust clouds that surround their young stars.
    Paradoxically, the most prolific star-forming galaxies and thus the most
    luminous are also the most difficult to study with optical telescopes
    like the Hubble Space Telescope because they are also the most obscured
    by dust. Determining the extremely high redshift of this object with
    millimetre waves is a highlight result from the LMT, which can see
    through the dust in the radio and millimetre wavelengths. The new
    object was first detected by astronomers using the Herschel space
    telescope, but for such distant objects, that instrument can take only
    relatively blurry pictures that yield little information.
    The LMT, located on the summit of a 15,000-foot extinct volcano in
    Mexico's central state of Puebla, began collecting its first light in
    2011 as a 32-metre millimetre-wavelength radio telescope. It has since
    been built out to its full 50-metre diameter and when fully operational
    this winter it will be the largest, most sensitive single-aperture
    instrument of its kind in the world. It is expected to be at the
    forefront of new discoveries about the oldest, most distant objects in
    the Universe. In millimetre wavelengths, one of the most common and
    easily detected spectral lines is that of carbon monoxide (CO), which
    the LMT was designed to trace. For independent confirmation of the
    large redshift observed, astronomers at the Harvard-Smithsonian Center
    for Astrophysics made additional observations with the Smithsonian
    Sub-millimeter Array telescope on Mauna Kea, Hawaii. That allowed the
    researchers to create a more detailed image of the new object, referred
    to as G09 83808, and to confirm its redshift with a carbon emission
    line. Further, the phenomenon of gravitational lensing, which appears
    to magnify objects whose light passes near massive objects, as predicted
    by Einstein's theory of general relativity, came into play in this
    study. A huge galaxy between the object G09 83808 and the observers
    on Earth acts as a magnifying glass and makes it look about 10 times
    brighter and closer than it really is. With the LMT coming fully online
    in the next couple of months, its higher resolution and higher sensiti-
    vity will enable astronomers to see more such distant objects.

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