THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 465 2018 March 18

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    THE SOCIETY FOR POPULAR ASTRONOMY
    Electronic News Bulletin No. 465 2018 March 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
    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/

    THE WORSENING COSMIC-RAY SITUATION
    Spaceweather.com

    New research conducted by the University of New Hampshire has revealed that
    radiation from deep space is dangerous and intensifying faster than was
    previously predicted. The story begins four years ago when scientists first
    sounded the alarm about cosmic rays. Analyzing data from the Cosmic Ray
    Telescope for the Effects of Radiation (CRaTER) instrument onboard NASA's
    Lunar Reconnaissance Orbiter (LRO), they found that cosmic rays in the
    Earth–Moon system were peaking at levels never before seen in the Space
    Age. The worsening radiation environment, they pointed out, was a potential
    peril to astronauts, curtailing how long they could safely travel through
    space. A figure from their original 2014 paper shows the number of days a
    30-year old male astronaut flying in a spaceship with 10 g/cm2 of aluminium
    shielding (a wall thickness of nearly 4 cm) could go before reaching NASA-
    mandated radiation limits. In the 1990s, the astronaut could spend 1000
    days in interplanetary space, but in 2014 only 700 days. Galactic cosmic
    rays come from outside the Solar System. They are a mixture of high-energy
    photons and sub-atomic particles accelerated towards the Earth by supernova
    explosions and other violent events in the cosmos. Our first line of
    defence is the Sun. The Sun's magnetic field and the solar wind combine to
    create a porous 'shield' that fends off cosmic rays attempting to enter the
    Solar System. The shielding action of the Sun is strongest during Solar
    Maximum and weakest during Solar Minimum. The problem is, as the authors
    note in their new paper, the shield is weakening. Over the last decade, the
    solar wind has exhibited low densities and magnetic field strengths,
    representing anomalous states that have not been observed previously during
    the Space Age. As a result of the remarkably weak solar activity, there
    have also been the highest fluxes of cosmic rays. In 2014, the team used a
    leading model of solar activity to predict how bad cosmic rays would become
    during the next Solar Minimum, now expected in 2019-2020. Their previous
    work suggested a ~20% increase of dose rates from one solar minimum to the
    next. In fact, the actual dose rates observed by CRaTER in the last 4 years
    exceed the predictions by ~10%, showing that the radiation environment is
    worsening even more rapidly than was expected.
    The data have come from CRaTER on the LRO spacecraft in orbit around the
    Moon, which is point-blank exposed to any cosmic radiation that the Sun
    allows to pass. Here on Earth, we have two additional lines of defence: the
    magnetic field and the atmosphere of our planet. Both mitigate cosmic rays.
    But even on Earth the increase is being felt. Scientists have been
    launching space-weather balloons to the stratosphere almost weekly since
    2015. Sensors onboard those balloons show a 13% increase in radiation
    (X-rays and gamma-rays) penetrating our planet's atmosphere. X-rays and
    gamma-rays detected by the balloons are 'secondary cosmic rays', produced
    by the crash of primary cosmic rays into the upper atmosphere. They trace
    radiation percolating down toward our planet's surface. The energy range of
    the sensors, 10 keV to 20 MeV, is similar to that of medical X-ray machines
    and airport security scanners. How does that affect us? Cosmic rays
    penetrate commercial airlines, dosing passengers and flight crews so much
    that pilots are classified by the International Commission on Radiological
    Protection as occupational radiation workers. Some research shows that
    cosmic rays can seed clouds and trigger lightning, potentially altering
    weather and climate. Furthermore, there are studies linking cosmic rays
    with cardiac arrhythmias in the general population. Cosmic rays can be
    expected to intensify even more in the years ahead as the Sun enters what
    may be the deepest Solar Minimum in more than a century.

    JUPITER'S JET STREAMS ARE VERY DEEP
    NASA/Jet Propulsion Laboratory

    Data collected by NASA's Juno mission to Jupiter indicate that the
    atmospheric winds of the gas-giant planet run deep into its atmosphere and
    last longer than similar atmospheric processes found here on Earth. The
    findings will improve understanding of Jupiter's interior structure, core
    mass and, eventually, its origin. Other Juno science results show that the
    massive cyclones that surround Jupiter's poles are enduring atmospheric
    features and unlike anything else encountered in the Solar System. The
    depth to which the roots of Jupiter's zones and belts extend has not been
    known until now. Gravity measurements collected by Juno during its close
    flybys of the planet have now provided an answer. On a gas planet,
    asymmetries can come only from flows deep within the planet; on Jupiter, the
    visible eastward and westward jet streams are asymmetric north and south.
    The deeper the jets, the more mass they contain, leading to a stronger
    signal expressed in the gravity field. Thus, the magnitude of the asymmetry
    in gravity is related to how deep the jet streams extend. Galileo viewed
    the stripes on Jupiter more than 400 years ago. Until now, we only had a
    superficial understanding of them and have been able to relate them to cloud
    features along Jupiter's jets. Now, after the Juno gravity measurements,
    we know how deep the jets extend and what their structure is beneath the
    visible clouds. The result was a surprise for the Juno science team because
    it indicated that the weather layer of Jupiter was so massive, extending
    much deeper than previously expected. The Jovian weather layer, from its
    very top to a depth of 3,000 kilometres, contains about one per cent of
    Jupiter's mass (about 3 Earth masses). That finding is important for
    understanding the nature and possible mechanisms driving the strong jet
    streams. In addition, the gravity signature of the jets is entangled with
    the gravity signal of Jupiter's core.
    Another Juno result suggests that beneath the weather layer, the planet
    rotates nearly as a rigid body. That is really unexpected, and future
    measurements by Juno will help scientists understand how the transition
    works between the weather layer and the rigid body below. The discovery has
    implications for other objects in the Solar System and beyond. The results
    imply that the outer differentially-rotating region should be at least three
    times deeper in Saturn and shallower in massive giant planets and brown-
    dwarf stars. Jupiter's poles are a stark contrast to the more familiar
    orange and white belts and zones encircling the planet at lower latitudes.
    The north pole is dominated by a central cyclone surrounded by eight
    circumpolar cyclones with diameters ranging from 4,000 to 4,600 kilometres.
    Jupiter's south pole also contains a central cyclone, but it is surrounded
    by five cyclones with diameters ranging from 5,600 to 7,000 kilometres.
    Almost all the polar cyclones, at both poles, are so densely packed that
    their spiral arms are in contact with adjacent cyclones. However, as
    tightly spaced as the cyclones are, they have remained distinct, with
    individual morphologies, over the seven months of observations.
    Juno was launched on 2011 August 5. It flies quite low over the planet's
    cloud tops — sometimes as close as about 3,500 kilometres. During such
    flybys, Juno is probing beneath the obscuring cloud cover of Jupiter and
    studying its aurorae to learn more about the planet's origins, structure,
    weather layer and magnetosphere.

    YOUNG STAR ENVELOPED BY HUGE DUST CLOUD
    NASA/Goddard Space Flight Center

    Astronomers have used the Hubble Space Telescope to uncover a vast, complex
    dust structure, about 2.5 light-years across, enveloping the young star HR
    4796A. A bright, narrow, inner ring of dust is already known to encircle the
    star and may have been corralled by the gravitational pull of an unseen
    giant planet. That newly discovered huge structure around the system may
    have implications for what the as-yet-unseen planetary system looks like
    around the 8-million-year-old star, which is in its formative years of
    planet construction. The debris field of very fine dust was probably
    created from collisions among developing planets near the star; that is
    sugested by a bright ring of dusty debris seen 75 AU from the star. The
    pressure of starlight from the star, which is 23 times more luminous than
    the Sun, then expelled the dust far into space. But the dynamics don't stop
    there. The puffy outer dust structure is like a doughnut-shaped tyre inner
    tube that got hit by a lorry. It is much more extended in one direction
    than in the other and so looks squashed on one side even after account is
    taken of its inclined projection on the sky. That may be due to the motion
    of the host star ploughing through the interstellar medium, or it may be
    influenced by a tidal tug from the star's red-dwarf binary companion
    (HR 4796 B), located at least 0.6 light-years from the primary star. Though
    debris discs have long been hypothesized, the first evidence for one around
    any star was not uncovered until 1983, by IRAS. Later photographs revealed
    an edge-on debris disc around the southern star Beta Pictoris. In the late
    1990s, Hubble's second-generation instruments, which could block out the
    glare of a central star, allowed many more discs to be photographed. Now,
    such debris rings are thought to be common around stars; about 40 such
    systems have been imaged to date, mostly by Hubble.

    EXOPLANET ATMOSPHERE OBSERVATIONS
    ESA/Hubble Information Centre

    An international team of scientists has used the Hubble Space Telescope to
    study the atmosphere of the hot exoplanet WASP-39b. By combining the new
    observations with older data they created the most complete study yet of an
    exoplanet atmosphere. The atmospheric composition of WASP-39b hints that
    the formation processes of exoplanets can be very different from those of
    our own Solar-System giants. WASP-39b is orbiting a Sun-like star about
    700 light-years away. The exoplanet is classified as a 'Hot-Saturn',
    reflecting both its mass being similar to that of the planet Saturn in our
    own Solar System and its distance from its parent star. The study found
    that the two planets, despite having a similar mass, are profoundly
    different in many ways. Not only is WASP-39b not known to have a ring
    system, it also has a puffy atmosphere that is free of high-altitude clouds.
    That characteristic allowed Hubble to see deep into its atmosphere. The
    team found clear spectroscopic evidence for atmospheric water vapour.
    In fact, WASP-39b has three times as much water as Saturn does. Although
    the researchers had predicted that they would see water vapour, they were
    surprised by the amount that they found. The water abundance allowed the
    team to infer the presence of large amount of heavier elements in the
    atmosphere. That in turn suggests that the planet was bombarded by a lot of
    icy material which gathered in its atmosphere. Such a bombardment would
    only be possible if WASP-39b formed much further away from its host star
    than it is at present.
    The analysis of the atmospheric composition and the current position of the
    planet indicate that WASP-39b most likely underwent an inward migration, a
    journey across its planetary system. Having made its inward journey
    WASP-39b is now only an eighth as far from its parent star, WASP-39, as
    Mercury is to the Sun, and it takes only four days to complete an orbit.
    The planet is also tidally locked, meaning that it always shows the same
    side to its star. The team measured the temperature of WASP-39b to be a
    scorching 750 degrees Celsius. Although only one side of the planet faces
    its parent star, powerful winds transport heat from the bright side around
    the planet, keeping the dark side almost as hot. Looking ahead, the team
    wants to use the James Webb Space Telescope — scheduled to be launched in
    2019 — to capture a more complete spectrum of the atmosphere of WASP-39b.
    The JWST will be able to collect data about the planet's atmospheric carbon,
    which absorbs light of longer wavelengths than Hubble can observe. From the
    amount of carbon and oxygen in the atmosphere, astronomers may be able to
    learn more about where and how the planet formed.

    DOUBT CAST ON HABITABILITY OF PROXIMA CENTAURI SYSTEM
    Carnegie Institution for Science

    A team of astronomers has detected a massive stellar flare — an energetic
    explosion of radiation — from the closest star to our own Sun, Proxima
    Centauri. That finding raises questions about the habitability of our Solar
    System's nearest exo-planetary neighbour, Proxima b, which orbits Proxima
    Centauri. The team discovered the enormous flare when it re-analyzed
    observations taken last year by ALMA, a radio telescope made up of 66
    antennae. At peak luminosity it was 10 times brighter than our Sun's
    largest flares when observed at similar wavelengths. Stellar flares have
    not been well studied at the wavelengths observed by ALMA, especially around
    stars of Proxima Centauri's type, called M dwarfs, which are the most common
    type in our Galaxy. The flare increased Proxima Centauri's brightness by
    1,000 times over 10 seconds. It was preceded by a smaller flare; taken
    together, the whole event lasted fewer than two minutes of the 10 hours that
    ALMA observed the star between January and March of last year. Stellar
    flares happen when a shift in the star's magnetic field accelerates
    electrons to speeds approaching that of light. The accelerated electrons
    interact with the highly charged plasma that makes up most of the star,
    causing an eruption that produces emission across the entire electromagnetic
    spectrum.
    It is likely that Proxima b was blasted by high-energy radiation during the
    flare. It was already known that Proxima Centauri experiences regular,
    although smaller, X-ray flares. Over the thousands of millions of years
    since Proxima b formed, such flares could have evaporated any atmosphere or
    ocean and sterilized the surface, so we are reminded that the habitability
    of a planet may involve more than just being the right distance from the
    host star to have liquid water. A November paper that also used the ALMA
    data on Proxima interpreted its average brightness, which included the light
    output of both the star and the flare together, as being caused by multiple
    discs of dust encircling the star, not unlike our own Solar System's
    asteroid and Kuiper belts. The authors of that study said that the presence
    of dust pointed to the existence of more planets or planetary bodies in the
    stellar system. But when the team looked at the ALMA data as a function of
    observing time, instead of averaging them all together, they were able to
    see the transient explosion of radiation emitted from Proxima Centauri for
    what it truly was. There is now no reason to think that there is a
    substantial amount of dust around Proxima, nor is there any information yet
    that indicates the star has a rich planetary system like ours.

    ULTRA-LUMINOUS SOURCES OF X-RAYS
    California Institute of Technology

    In the 1980s, researchers began discovering extremely bright sources of
    X-rays in the outer portions of galaxies, away from the supermassive black
    holes that dominate their centres. At first, researchers thought that those
    cosmic objects, called ultra-luminous X-ray sources, or ULXs, were hefty
    black holes with more than ten times the mass of the Sun. But observations
    beginning in 2014 from NuSTAR and other space telescopes are showing that
    some ULXs, which glow with X-ray light equal in energy to millions of Suns,
    are actually neutron stars — the burnt-out cores of massive stars that
    exploded. Three such ULXs have been identified as neutron stars so far.
    Now, a team of astronomers using data from the Chandra X-ray Observatory has
    identified a fourth ULX as being a neutron star — and found new clues about
    how those objects can shine so brightly.
    Neutron stars are extremely dense objects. Their gravity pulls surrounding
    material from companion stars onto them, and as that material is pulled in,
    it heats up and glows with X-rays. But as the neutron stars 'feed' on the
    matter, there comes a time when the resulting X-ray light pushes the matter
    away. Astronomers call that point — when the objects cannot accumulate
    matter any faster and or give off any more X-rays — the Eddington limit.
    In the same that we can eat only so much food at a time, there are limits to
    how fast neutron stars can accrete matter. But ULXs are somehow breaking
    that limit to give off such incredibly bright X-rays, and we don't know why.
    In the new study, the researchers looked at a ULX in M51, the Whirlpool
    galaxy, which is about 28 million light-years away. They analyzed archival
    X-ray data taken by Chandra and discovered an unusual dip in the ULX's
    spectrum. After ruling out all other possibilities, they concluded that
    the dip was from a phenomenon called cyclotron resonance scattering, which
    occurs when charged particles — either positively charged protons or
    negatively charged electrons — circle in a magnetic field. Black holes
    don't have magnetic fields and neutron stars do, so the finding indicated
    that that particular ULX in M51 had to be a neutron star.
    Cyclotron resonance scattering creates tell-tale signatures in a star's
    optical spectrum, and the presence of those signatures, called cyclotron
    lines, can provide information about the strength of the star's magnetic
    field — but only if the cause of the lines, whether it be protons or
    electrons, is known. The researchers have not got a sufficiently detailed
    spectrum of the new ULX to say for certain. If the cyclotron line is from
    protons, then we know that the magnetic fields around the neutron star are
    extremely strong and may in fact be helping to break the Eddington limit.
    Such strong magnetic fields could reduce the pressure from a ULX's X-rays —
    the pressure that normally pushes matter away — allowing the neutron star
    to consume more matter than is typical and to shine with the extremely
    bright X-rays. If the cyclotron line is from circling electrons, in
    contrast, then the magnetic field strength around the neutron star would not
    be exceptionally strong, and thus the field is probably not the reason that
    the stars break the Eddington limit. To address the problem further, the
    researchers are planning to acquire more X-ray data on the ULX in M51 and
    look for more cyclotron lines in other ULXs. The discovery that those very
    bright objects, long thought to be black holes with masses up to 1,000 times
    that of the Sun, are powered by much less massive neutron stars, was a huge
    scientific surprise. Now astronomers might actually be getting firm
    physical clues as to how such relatively small objects can be so mighty.

    SEARCH FOR FIRST STARS UNCOVERS DARK MATTER
    American Friends of Tel Aviv University

    A team of astronomers has unexpectedly stumbled upon 'dark matter', the most
    mysterious building block of outer space, while attempting to detect the
    earliest stars in the Universe through radio-wave signals. The idea that
    those signals implicate dark matter is put forward in a paper that suggests
    that the signal is proof of interactions between normal matter and dark
    matter in the early Universe. The discovery offers a rather direct proof
    that dark matter exists and that it is composed of low-mass particles. The
    signal, recorded by a novel radio telescope called EDGES, dates to 180
    million years after the Big Bang. Dark matter is thought to be the key to
    determining what the Universe is made of. We know quite a bit about the
    chemical elements that make up the Earth, the Sun and other stars, but most
    of the matter in the Universe is invisible and known as simply as 'dark
    matter'. The existence of dark matter is inferred from its gravitational
    effects, but we have no idea what kind of substance it is. Hence, dark
    matter remains one of the greatest mysteries in physics. To solve it, we
    must travel back in time. Astronomers can see back in time, since it takes
    light time to reach us. We see the Sun as it was eight minutes ago, while
    the immensely distant first stars in the Universe appear to us on Earth as
    they were thousands of millions of years in the past. The team reported the
    detection of a radio signal at a frequency of 78 megahertz. The width of
    the observed profile was largely consistent with expectations, but they also
    found it had a larger amplitude (corresponding to deeper absorption) than
    predicted, indicating that the primordial gas was colder than expected. It
    is suggested that the gas cooled through the interaction of hydrogen with
    cold, dark matter.
    That surprising signal indicates the presence of two actors: the first
    stars, and dark matter. The first stars in the Universe turned on the radio
    signal, while the dark matter collided with the ordinary matter and cooled
    it down. Extra-cold material naturally explains the strong radio signal.
    Physicists expected that any such dark matter particles would be heavy, but
    the discovery indicates low-mass particles. On the basis of the radio
    signal, it is argued that the dark-matter particle is no more massive than
    several proton masses. That insight alone has the potential to reorient the
    search for dark matter. Once stars formed in the early Universe, their
    light was predicted to have penetrated the primordial hydrogen gas, altering
    its internal structure. That would cause the hydrogen gas to absorb photons
    from the cosmic microwave background, at the specific wavelength of 21 cm,
    imprinting a signature in the radio spectrum that should be observable today
    at radio frequencies below 200 megahertz. The new observation matches that
    prediction except for the unexpected depth of the absorption. The team
    predicts that the dark matter produced a very specific pattern of radio
    waves that can be detected with a large array of radio antennae. One such
    array is the SKA, the largest radio telescope in the world, now under
    construction. Such an observation with the SKA would confirm that the first
    stars did indeed reveal dark matter.

    FIRST LIGHT ON VLT INTERFEROMETER
    ESO

    The new MATISSE instrument on ESO's Very Large Telescope Interferometer
    (VLTI) has now successfully made its first observations at the Paranal
    Observatory in northern Chile. MATISSE is the most powerful interferometric
    instrument in the world at mid-infrared wavelengths. It will use high-
    resolution imaging and spectroscopy to probe the regions around young stars
    where planets are forming as well as the regions around supermassive black
    holes in the centres of galaxies. The first MATISSE observations used the
    VLTI's Auxiliary Telescopes to examine some of the brightest stars in the
    night sky, including Sirius, Rigel and Betelgeuse, and showed that the
    instrument is working well. MATISSE (Multi AperTure mid-Infrared Spectro-
    Scopic Experiment) observes infrared light of wavelengths from 3 to 13
    microns. It is a second-generation spectro-interferometer instrument for
    the VLT and takes advantage of the multiple telescopes coupled with the wave
    nature of the light. It can produce more detailed images of celestial
    objects than can be obtained with any existing or planned single telescope
    at those wavelengths. The initial MATISSE observations of the red super-
    giant star Betelgeuse, which is expected to explode as a supernova in a few
    hundred thousand years, showed that it still has secrets to reveal. The
    star appears to be of different sizes when seen at different wavelengths.
    Such data will allow astronomers to study further the huge star's surround-
    ings and how it is shedding material into space. MATISSE will contribute to
    several fundamental research areas in astronomy, focusing in particular on
    the inner regions of discs around young stars where planets are forming, the
    study of stars at different stages of their lives, and the surroundings of
    supermassive black holes at the centres of galaxies. MATISSE is a four-way
    beam combiner, i.e. it combines the light collected from up to four of the
    8.2-m VLT Unit Telescopes or up to four of the Auxiliary Telescopes (ATs)
    that make up the VLTI, performing both spectroscopic and imaging observa-
    tions. In doing so, MATISSE and the VLTI together possess the imaging power
    of a telescope up to 200 metres in diameter, capable of producing the most
    detailed images ever obtained at mid-infrared wavelengths.

    Bulletin compiled by Clive Down (c) 2018 The Society for Popular Astronomy
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