SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 458 2017 December 3

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    The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 458 2017 December 3
    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/

    EARTH STOPS HIGH-ENERGY NEUTRINOS
    Penn State

    For the first time, an experiment has measured the Earth's ability to
    absorb neutrinos — the smaller-than-an-atom particles that zoom
    throughout space and through us by the billions every second at nearly
    the speed of light. The experiment was achieved with the IceCube
    detector, an array of 5,160 basketball-sized sensors frozen deep within
    a cubic kilometre of very clear ice near the South Pole. The first
    detections of extremely-high-energy neutrinos were made by IceCube in
    2013, but a question remained as to whether any kind of matter could
    truly stop a neutrino's journey through space. Astronomers knew that
    lower-energy neutrinos pass through just about anything, but although
    they had expected higher-energy neutrinos to be different, no previous
    experiments had been able to demonstrate convincingly that higher-energy
    neutrinos could be stopped by anything. The results are based on one
    year of data from about 10,800 neutrino-related interactions. This
    new discovery with IceCube is an interesting addition to our deepening
    understanding of how the Universe works. It also is a little bit of a
    disappointment for those who hope for an experiment that will reveal
    something that cannot be explained by the current Standard Model of
    Particle Physics. The results of this Ice Cube study are fully consis-
    tent with that model — the reigning theory that for the past half-
    century has described all the physical forces in the universe except
    gravity.
    Neutrinos were first formed at the beginning of the Universe, and they
    continue to be produced by stars throughout space and by nuclear
    reactors on Earth. IceCube's sensors do not directly observe neutrinos,
    but instead measure flashes of blue light, known as Cherenkov radiation,
    emitted after a series of interactions involving fast-moving charged
    particles that are created when neutrinos interact with the ice. By
    measuring the light patterns from those interactions in or near the
    detector array, IceCube can estimate the neutrinos' energies and
    directions of travel. The scientists found that the neutrinos that had
    to travel the furthest through the Earth were less likely to reach the
    detector. Most of the neutrinos selected for this study had more than
    a million times as much energy as those produced by more familiar
    sources, like the Sun or nuclear power plants. The analysis also
    included a small number of astrophysical neutrinos, which are produced
    outside the Earth's atmosphere, from cosmic accelerators unidentified to
    date, perhaps associated with supermassive black holes. In addition to
    providing the first measurement of the Earth's absorption of neutrinos,
    the analysis shows that IceCube's scientific reach extends beyond its
    core focus on particle-physics discoveries and the emerging field of
    neutrino astronomy into the fields of planetary science and nuclear
    physics. This analysis is also of interest to geophysicists who would
    like to use neutrinos to image the Earth's interior in order to explore
    the boundary between the Earth's solid inner core and its liquid outer
    core. Physicists now hope to repeat the study using an expanded, multi-
    year analysis of data from the full 86-string IceCube array, and to look
    at higher ranges of neutrino energies for any hints of new physics
    beyond the Standard Model.

    MARS WATER WAS JUST SAND AND DUST AVALANCHES
    NASA

    In 2015 September, scientists mistakenly announced that Mars had liquid
    water flowing on its surface. Now, a team of scientists from the U.S.
    Geological Survey has reinterpreted the findings and says that the
    surface features are, in fact, likely to be avalanches of sand and dust.
    The study re-examined the original data from NASA that looked at the
    Recurring Slope Lineae, or RSL. That area is a narrow, sloping surface
    where the features appear to be darker than the rest of their
    surroundings. They were found to fade and reappear at regular
    intervals, returning during the warmest time of the year. When the
    streaks were first discovered, scientists believed that they had
    convincing evidence that appeared to confirm that water — albeit briny
    — is flowing today on the surface of Mars. The announcement generated
    huge excitement at the time — the implications of such a finding
    increased the likelihood that life once existed, and could still exist,
    on Mars.
    The latest findings dash such hopes. Scientists thought of RSL as
    possible liquid-water flows, but now say the slopes are more like what
    we expect for dry sand. The new understanding of RSL supports other
    evidence that shows that Mars today is very dry. Findings showed that
    the RSL slopes are similar to those in areas where the movement of sand
    dunes causes such features to appear. The scientists say that water is
    highly unlikely to be responsible — the amount of water required does
    not correspond to what the data are showing. Also, they say that it is
    highly unlikely that water is only produced at the top of slopes — it
    should appear on lower slopes too. The findings do not rule out the
    possibility of liquid water on Mars or that it could play a role in the
    movement of dust and sand — potentially initiating the avalanches that
    the scientists suggest are responsible for the features.

    PLUTO IS COLDER THAN EXPECTED
    University of California – Santa Cruz
    The gas composition of a planet's atmosphere generally determines how
    much heat gets trapped in the atmosphere. For the dwarf planet Pluto,
    however, the predicted temperature based on the composition of its
    atmosphere was much higher than actual measurements taken by the New
    Horizons spacecraft in 2015. A new study proposes a novel cooling
    mechanism controlled by haze particles to account for Pluto's frigid
    atmosphere. The cooling mechanism involves the absorption of heat by
    the haze particles, which then emit infrared radiation, cooling the
    atmosphere by radiating energy into space. The result is an atmospheric
    temperature of about minus 203 degrees Celsius instead of the predicted
    minus 173 Celsius. The excess infrared radiation from haze particles
    in Pluto's atmosphere should be detectable by the James Webb Space
    Telescope, allowing confirmation of the hypothesis after the telescope's
    planned launch in 2019. Extensive layers of atmospheric haze can be
    seen in images of Pluto taken by New Horizons. The haze results from
    chemical reactions in the upper atmosphere, where ultraviolet radiation
    from the Sun ionizes nitrogen and methane, which react to form tiny
    hydrocarbon particles tens of nanometres in diameter. As those tiny
    particles sink down through the atmosphere, they stick together to form
    aggregates that grow larger as they descend, eventually settling onto
    the surface. The researchers are interested in studying the effects of
    haze particles on the atmospheric energy balance of other planetary
    bodies, such as Neptune's moon Triton and Saturn's moon Titan. Their
    findings may also be relevant to investigations of exoplanets with hazy
    atmospheres.

    FIRST INTERSTELLAR ASTEROID IS NOTHING LIKE SEEN BEFORE
    ESO

    On 2017 October 19 the Pan-STARRS 1 telescope in Hawaii observed a
    faint point of light moving across the sky. It looked initially like a
    typical fast-moving small asteroid, but additional observations over
    the next couple of days allowed its orbit to be computed fairly
    accurately. The orbit calculations revealed beyond any doubt that
    that body did not originate from inside the Solar System, like all
    other asteroids or comets ever observed, but instead had come from
    interstellar space. Although it was originally classified as a comet,
    observations from ESO and elsewhere revealed no signs of cometary
    activity after it passed closest to the Sun in 2017 September. The
    object was re-classified as an interstellar asteroid and named
    1I/2017 U1 (`Oumuamua). ESO's Very Large Telescope was immediately
    called into action to measure the object's orbit, brightness and colour
    more accurately than smaller telescopes could achieve. Speed was vital
    as `Oumuamua was rapidly fading as it headed away from the Sun and past
    the Earth's orbit, on its way out of the Solar System. There were more
    surprises to come. Combining the images from the FORS instrument on the
    VLT through four different filters with those of other large telescopes,
    the team of astronomers found that `Oumuamua varies dramatically in
    brightness by a factor of ten as it spins on its axis every 7.3 hours.
    That unusually large variation in brightness means that the object is
    highly elongated, about ten times as long as it is wide, with a complex,
    convoluted shape. They also found that it has a dark red colour,
    similar to objects in the outer Solar System, and confirmed that it
    is completely inert, without the faintest hint of dust around it.
    Those properties suggest that `Oumuamua is dense, possibly rocky or with
    high metal content, lacks significant amounts of water or ice, and that
    its surface is now dark and reddened owing to the effects of irradiation
    from cosmic rays over millions of years. It is estimated to be at least
    400 metres long. Preliminary orbital calculations suggested that the
    object has come from the approximate present direction of Vega. However,
    it has taken it so long for it to make the journey to the Solar System,
    even though it has been travelling at a speed of about 26 km/s (95,000
    km/h), that Vega was not near that position when the asteroid was there
    about 300,000 years ago. `Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the Solar System. Astronomers estimate that interstellar asteroids similar to `Oumuamua pass through the inner Solar System about once a year, but they are faint and hard to spot and so have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS, were made powerful enough to have a chance of discovering them. Astronomers are continuing to observe this unique object and hope to pin down more accurately where it came from and where it is going next on its tour of the Galaxy.

    EXOPLANET 55 CANCRI e LIKELY TO HAVE ATMOSPHERE
    NASA/JPL

    Twice as big as the Earth, the super-Earth 55 Cancri e was thought to
    have lava flows on its surface. The planet is very close to its star,
    and the same side of the planet always faces the star, so the planet has
    permanent day and night sides. On the basis of a 2016 study using data
    from the Spitzer Space Telescope, scientists speculated that lava would
    flow freely in lakes on the starlit side and become hardened on the face
    in perpetual darkness. The lava on the day side would reflect radiation
    from the star, contributing to the overall observed temperature of the
    planet. Now, a deeper analysis of the same Spitzer data finds that the
    planet probably has an atmosphere whose ingredients could be similar to
    those of the Earth's atmosphere, but thicker. Scientists have said that
    lava lakes directly exposed to space without an atmosphere would create
    local hot spots of high temperatures, so they are not the best expla-
    nation for the Spitzer observations. Using an improved model of how
    energy would flow throughout the planet and radiate back into space,
    researchers find that the night side of the planet is not as cool as
    previously thought. Even the 'cool' side is still quite toasty by
    Earthly standards, at an average of 1,300 to 1,400 Celsius, and the
    hot side averages 2,300 Celsius. The difference between the hot and
    cold sides would be more extreme if there were no atmosphere.
    Researchers say that the atmosphere of the extraordinary planet could
    contain nitrogen, water and even oxygen — molecules found in *our*
    atmosphere, too — but with much higher temperatures throughout. The
    density of the planet is also similar to that of the Earth, suggesting
    that it, too, is rocky. The intense heat from the host star would be
    far too great to support life, however, and could not allow liquid
    water. Spitzer observed 55 Cancri e between 2013 June 15 and July 15,
    using a camera specially designed for viewing infrared light, which is
    an indicator of heat energy. By comparing changes in brightness
    observed by Spitzer to energy-flow models, researchers realized that an
    atmosphere with volatile materials could best explain the temperatures.
    There are many open questions about 55 Cancri e, especially why the
    atmosphere has not been stripped away from the planet, given the
    perilous radiation environment of the star. Understanding that planet
    could help us address larger questions about the evolution of rocky
    planets.

    SPACE DUST MAY TRANSPORT LIFE BETWEEN WORLDS
    University of Edinburgh

    Fast-moving flows of interplanetary dust that continually bombard our
    planet's atmosphere could deliver tiny organisms from far-off worlds, or
    send Earth-based organisms to other planets, according to new research.
    The dust streams could collide with biological particles in the Earth's
    atmosphere with enough energy to knock them into space. Such an event
    could enable bacteria and other forms of life to make their way from one
    planet in the Solar System to another and perhaps beyond. The finding
    suggests that large asteroid impacts may not be the sole mechanism by
    which life could transfer between planets, as was previously thought.
    The research calculated how powerful flows of space dust — which can
    move at up to 70 km/s — could collide with particles in our atmospheric
    system. It found that small particles existing at 150 km or higher
    above the Earth's surface could be knocked beyond retrieval by the
    Earth's gravity by space dust and eventually reach other planets. The
    same mechanism could enable the exchange of atmospheric particles
    between distant planets. Some bacteria, plants and small animals called
    tardigrades are known to be able to survive in space, so it is possible
    that such organisms — if present in the Earth's upper atmosphere —
    might collide with fast-moving space dust and withstand a journey to
    another planet. The proposition that space-dust collisions could propel
    organisms over enormous distances between planets raises some exciting
    prospects of how life and the atmospheres of planets originated. The
    streaming of fast space dust is found throughout planetary systems and
    could be a common factor in proliferating life.

    NEARBY STARS AMONG OLDEST IN GALAXY
    Georgia State University

    Astronomers have discovered some of the oldest stars in our Milky Way
    galaxy by determining their locations and velocities. A bit like humans,
    stars have a life span: birth, youth, adulthood, seniority and death.
    The study focussed on certain old stars, those known as cool subdwarfs,
    that are much older and cooler than the Sun. The oldest stars are about
    six to nine billion years old. They are found in the Galaxy's halo,
    a roughly spherical component of the Galaxy that formed first, in which
    old stars move in orbits that are highly elongated and tilted. Younger
    stars in the Milky Way revolve together within the Galaxy's disc in
    roughly circular orbits. In the reported study, astronomers conducted a
    census of the solar neighbourhood to identify how many young, adult and
    old stars are present. They targeted stars out to a distance of 200
    light-years, which is relatively nearby in relation to a galaxy that is
    more than 100,000 light-years across. That is further than the tradi-
    tional horizon for the region of space that is referred to as 'the solar
    neighborhood', which is about 80 light-years in radius. The astronomers
    first observed the stars over many years with the 0.9-m telescope at
    CTIO in the foothills of the Chilean Andes. They measured the stars'
    positions and were able to determine their motions across the sky, their
    distances and whether or not each star had an unseen companion orbiting
    it. The team's work increased the known population of old stars in our
    solar neighbourhood by 25%. Among the new sub-dwarfs, the researchers
    discovered two old binary stars, even though older stars are typically
    found to be alone, rather than in pairs.
    The team also outlined two methods to identify such rare old stars. One
    method uses stars' locations in the Hertzsprung-Russell (H-R) diagram.
    The old stars are found below the sequence of dwarf stars in the H-R
    diagram, hence the name 'sub-dwarfs'. Astronomers then looked at one
    particular characteristic of known subdwarf stars — how fast they move
    across the sky. The research showed that if a star has a tangential
    velocity greater than 200 km/s, it has to be old. So on the basis of
    their movements in our Galaxy, it can be possible to decide whether a
    star is an old subdwarf or not. In general, the older a star is, the
    faster it moves. The team applied the tangential-velocity cut-off and
    compared stars in the sub-dwarf region of the H-R diagram to other
    existing stellar data-bases, and identified an additional 29 previously
    unrecognized old-star candidates. In 2018, results from the Gaia
    mission, which is measuring accurate positions and distances for
    millions of stars in the Milky Way, will make finding older stars much
    easier for astronomers. Determining the distances of stars is now very
    labour-intensive and requires a lot of telescope time and patience.
    Because the Gaia mission will provide a much larger sample size, the
    limited sample of sub-dwarfs will grow, and the rarest of those rare
    stars — binary sub-dwarfs — will be revealed.

    DO DARK MATTER AND DARK ENERGY REALLY EXIST?
    Universite de Geneve

    For close on a century, researchers have hypothesized that the Universe
    contains matter that can not be directly observed, known as 'dark
    matter'. They have also posited the existence of a 'dark energy' that
    is more powerful than gravitational attraction. Those two hypotheses,
    it has been argued, account for the movement of stars in galaxies and
    for the accelerating expansion of the Universe respectively. But —
    according to a researcher at the University of Geneva — those concepts
    may not be valid: the phenomena that they are supposed to describe can
    be demonstrated without them. The research exploits a new theoretical
    model based on the scale invariance of the empty space, potentially
    solving two of astronomy's greatest problems. In 1933, the Swiss
    astronomer Fritz Zwicky claimed that there was substantially more matter
    in the Universe than we can actually see. Astronomers called that
    unknown matter 'dark matter', a concept that was to take on yet more
    importance in the 1970s, when the US astronomer Vera Rubin called on
    it to explain the movements and speed of the stars. Scientists have
    subsequently devoted considerable resources to identifying dark matter
    — in space, on the ground and even at CERN — but without success. In
    1998 a second problem arose: a team of Australian and US astrophysicists
    discovered the acceleration of the expansion of the Universe, earning
    them after some delay the Nobel Prize for physics in 2011. However, in
    spite of much effort, no theory or observation has been able to define
    the black energy that is allegedly stronger than Newton's gravitational
    attraction. In short, dark matter and dark energy are two problems that
    have stumped astronomersfor over 80 years and 20 years respectively.
    The way we represent the Universe and its history are described by
    Einstein's equations of general relativity, Newton's universal gravita-
    tion and quantum mechanics. The model-consensus at present is that of a
    big bang followed by an expansion. In that model, there is a starting
    hypothesis that seems not to have been taken into account. That is the
    scale invariance of the empty space; in other words, the empty space and
    its properties do not change following a dilation or contraction. The
    empty space plays a primordial role in Einstein's equations as it
    operates in a quantity known as the 'cosmological constant', and the
    resulting Universe model depends on it. On the basis of that hypothesis,
    researchers are now re-examining the model of the Universe, pointing out
    that the scale invariance of the empty space is also present in the
    fundamental theory of electromagnetism.

    When the researchers carried out cosmological tests on the new model,
    they found that it matched the observations. They also found that the
    model predicts the accelerated expansion of the Universe without having
    to factor in any particle or dark energy. In short, it appears that
    dark energy may not actually exist, since the acceleration of the
    expansion is contained in the equations of the physics. In a second
    stage, astronomers focussed on Newton's law, a special case of the
    equations of general relativity. The law is also slightly modified when
    the model incorporates the new hypothesis. Indeed, it contains a very
    small outward acceleration term, which is particularly significant at
    low densities. The amended law, when applied to clusters of galaxies,
    leads to masses of clusters in line with that of visible matter
    (contrary to what Zwicky argued in 1933): that means that no dark matter
    is needed to explain the high speeds of the galaxies in the clusters.
    A second test demonstrated that the law also predicts the high speeds
    reached by the stars in the outer regions of galaxies (as Rubin had
    observed), without having to turn to dark matter to describe them.
    Finally, a third test looked at the dispersion of the speeds of the
    stars oscillating around the plane of the Milky Way. That dispersion,
    which increases with the age of the relevant stars, can be explained
    very well by the invariant empty space hypothesis, while there was
    previously no agreement on the origin of that effect.

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