THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 479 2018 Nov 4th

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    THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 479 2018 November 4

    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
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    A team of Hungarian astronomers may have confirmed two elusive clouds of
    dust, in semi-stable points just 400,000 kilometres from the Earth. The
    clouds, first reported by and named for Polish astronomer Kazimierz
    Kordylewski in 1961, are extraordinarily faint, so their existence is
    controversial. The Earth–Moon system has five points of stability where
    gravitational forces maintain the relative positions of objects located
    there. Two of those so-called Lagrange points, L4 and L5, form an
    equilateral triangle with the Earth and Moon, and move around the Earth as
    the Moon moves along its orbit. L4 and L5 are not completely stable, as
    they are disturbed by the gravitational pull of the Sun. Nonetheless they
    are thought to be locations where interplanetary dust might collect, at
    least temporarily. Kordylewski observed two nearby clusters of dust at L5
    in 1961, with various reports since then, but their extreme faintness makes
    them difficult to detect and many scientists doubted their existence. In a
    paper earlier this year the Hungarian team modelled the Kordylewski clouds
    to assess how they form and how they might be detected. The researchers
    were interested in their appearance with polarising filters, which transmit
    light with a particular direction of oscillation, similar to those in some
    types of sunglasses; scattered or reflected light is always more or less
    polarised, depending on the angle of scattering or reflection. They then
    set out to find the dust clouds. With a linearly polarising filter system
    attached to a camera lens and CCD detector, the scientists took exposures of
    the purported location of the Kordylewski cloud at the L5 point. The images
    they obtained show polarised light reflected from dust, extending well
    outside the field of view of the camera lens.
    The observed pattern matches predictions made by the same group of
    researchers in an earlier paper and is consistent with the earliest
    observations of the Kordylewski clouds 60 years ago. Astronomers were able
    to rule out optical artefacts and other effects, so the presence of the dust
    cloud is confirmed. The Kordylewski clouds are two of the toughest objects
    to find, and though they are as close to the Earth as the Moon are largely
    overlooked by researchers in astronomy. It is intriguing to confirm that
    our planet has dusty pseudo-satellites in orbit alongside our lunar
    neighbour. Given their stability, the L4 and L5 points are seen as
    potential sites for orbiting space probes, and as transfer stations for
    missions exploring the wider Solar System. There are also proposals to
    store pollutants at the two points. Future research will look at L4 and L5,
    and the associated Kordylewski clouds, to understand how stable they really
    are, and whether their dust presents any kind of threat to equipment and
    future astronauts.


    The Moon may be the key to unlocking how the first stars and galaxies shaped
    the early Universe. A team of astronomers observed the Moon with a radio
    telescope to help search for the faint signal from hydrogen atoms. Before
    there were stars and galaxies, the Universe was pretty much just hydrogen,
    floating around in space. Since there are no sources of the optical light
    visible to our eyes, that early stage of the Universe is known as the
    'cosmic dark ages'. The astronomers describe how they have used the
    Murchison Widefield Array (MWA) radio telescope to help search for radio
    signals given off by the hydrogen atoms.
    The radio signal from the early Universe is very weak compared to the
    extremely bright objects in the foreground, which include accreting black
    holes in other galaxies and electrons in our own Milky Way. The key to
    solving that problem is being able precisely to measure the average
    brightness of the sky. However, built-in effects from the instruments and
    radio-frequency interference make it difficult to get accurate observations
    of the very faint radio signal. In their work, the astronomers used the
    Moon as a reference point of known brightness and shape. That allowed them
    to measure the brightness of the Milky Way at the position of the occulting
    Moon. The astronomers also took into account 'earthshine' radio waves from
    the Earth that reflect off the Moon and back onto the telescope. Earthshine
    corrupts the signal from the Moon and the team had to remove that contam-
    ination from their analysis. If astronomers can detect that radio signal it
    will tell us whether our theories about the evolution of the Universe are
    correct. With more observations, the astronomers hope to uncover the
    hydrogen signal and put theoretical models of the Universe to the test.


    Astronomers are calling Comet 46P/Wirtanen the “comet of the year”. Seven
    weeks from now, on Dec. 16, the kilometre-wide ball of dirty ice will come
    within 11.5 million km of the Earth — making it one of the 10 closest-
    approaching comets of the Space Age. Comet 46P/Wirtanen will probably
    become a naked-eye object for several weeks around Christmas. Pictures
    taken with a 12-inch telescope show the comet's green atmosphere which is,
    impressively, almost twice the angular size of the planet Jupiter. The
    green colour comes from diatomic carbon (C2) — a gaseous substance common
    in comet atmospheres that glows green in the near-vacuum of space. At the
    moment, the integrated brightness of the comet is similar to that of a
    10th-magnitude star. However, it is expected to brighten more than 200-fold
    by December. If current trends hold, 46P could ultimately reach magnitude
    +3, making it not a Great Comet but a very good one, visible to the unaided
    eye and an easy target for binoculars or small telescopes. Comet Wirtanen
    passes through the inner Solar System every 5.4 years. Right now it is near
    the orbit of Mars, and is heading in our direction.


    Astronomers have discovered two stars in a binary pair that complete an
    orbit around one another in a little over three hours, residing in the
    planetary nebula M3-1. Remarkably, the stars could drive a nova explosion,
    an entirely unexpected event according to current understanding of binary-
    star evolution. Planetary nebulae are the glowing shells of gas and dust
    formed from the outer layers of stars like our own Sun, which they throw off
    during the final stages of their evolution. In many cases, interaction with
    a nearby companion star plays an important role in the ejection of that
    material and the formation of the elaborate structures seen in the resulting
    planetary nebulae. The planetary nebula M3-1 is located in the constella-
    tion Canis Major, at a distance of roughly 14,000 light-years. M3-1 was a
    firm candidate to host a binary central star, as its structure with prom-
    inent jets and filaments is typical of binary-star interactions. Using the
    telescopes of the European Southern Observatory in Chile, the team looked
    at M3-1 over a period of several years. In the process they discovered and
    studied the binary star in the centre of the nebula.
    The two stars are so close together that they cannot be resolved from the
    ground, so instead the presence of the second star is inferred from the
    variation of their observed combined brightness — most obviously by
    periodic eclipses of one star by the other, which produce marked drops in
    the brightness. The team discovered that the central star of the planetary
    nebula M3-1 has one of the shortest orbital periods of binary central stars
    known to date, at just over three hours. The ESO observations also show
    that the two stars — most likely a white dwarf with a low-mass main-
    sequence companion — are almost touching. As a result, the pair is likely
    to undergo a nova eruption, the result of the transfer of material from one
    star to the other. When the recipient star reaches a critical mass, a
    violent thermonuclear explosion takes place and the system temporarily
    increases in brightness by up to a million times. Theory suggests that
    binary stars should be well separated after the formation of a planetary
    nebula. It should then take a long time before they begin to interact again
    and events such as novae become possible. In 2007, astronomers observed a
    different nova explosion, known as Nova Vul 2007, inside another planetary
    nebula. The 2007 event was particularly difficult to explain. By the time
    the two stars are close enough for a nova, the material in the planetary
    nebula should have expanded and dissipated so much that it is no longer
    visible. The new event adds to the conundrum. Among the stars in the
    centre of M3-1, there is another candidate for a similar nova eruption in
    the relatively near future.


    New research has found evidence for a large number of double supermassive
    black holes, probably precursors of gigantic black-hole merging events.
    That confirms the current understanding of cosmological evolution — that
    galaxies and their associated black holes merge over time, forming bigger
    and bigger galaxies and black holes. Astronomers have looked at radio maps
    of powerful jet sources and found signs that would usually be present when
    looking at black holes that are closely orbiting each other. Before black
    holes merge they form a binary black hole, where the two black holes orbit
    around one another. Gravitational-wave telescopes have been able to record
    the merging of smaller black holes since 2015, by measuring the strong
    bursts of gravitational waves that are emitted when binary black holes
    merge, but current technology cannot be used to demonstrate the presence of
    supermassive binary black holes. Supermassive black holes emit powerful
    jets. When supermassive binary black holes orbit, they cause the jet
    emanating from the nucleus of a galaxy periodically to change its direction.
    Astronomers studied the directions in which such jets are emitted, and
    variances in those directions; they compared the direction of the jets with
    that of one of the radio lobes (that store all the particles that ever went
    through the jet channels) to demonstrate that that method can be used to
    indicate the presence of supermassive binary black holes. The fact that
    the most powerful jets are associated with binary black holes could have
    important consequences for the formation of stars in galaxies: stars form
    from cold gas, jets heat that gas and thus suppress the formation of stars.
    A jet that always heads in the same direction only heats a limited amount of
    gas in its vicinity. However, jets from binary black holes change direction
    continuously. Therefore, they can heat much more gas, suppressing the
    formation of stars much more efficiently, and thus contributing towards
    keeping the number of stars in galaxies within the observed limits.

    University of Maryland

    On 2017 October 16, an international group of astronomers and physicists
    excitedly reported the first simultaneous detection of light and
    gravitational waves from the same source — a merger of two neutron stars.
    Now, a of astronomers has identified a direct relative of that historic
    event. The newly described object, named GRB150101B, was reported as a
    gamma-ray burst localized by NASA's Neil Gehrels Swift Observatory in 2015.
    Follow-up observations suggest that GRB150101B shares remarkable similari-
    ties with the neutron-star merger, named GW170817, discovered by the Laser
    Interferometer Gravitational-wave Observatory (LIGO) and observed by
    multiple light-gathering telescopes in 2017. A new study suggests that
    those two separate objects may, in fact, be directly related. The team
    suspects that both GRB150101B and GW170817 were produced by the same type of event: a merger of two neutron stars. Such catastrophic coalescences each generated a narrow jet, or beam, of high-energy particles. The jets each
    produced a short, intense gamma-ray burst (GRB) — a powerful flash that
    lasts only a few seconds. GW170817 also created ripples in space-time
    called gravitational waves, suggesting that that might be a common feature
    of neutron-star mergers. The apparent match between GRB150101B and GW170817 is striking: both produced an unusually faint and short-lived gamma-ray burst and both were sources of bright, blue optical light and long-lasting
    X-ray emission. The host galaxies are also remarkably similar, according to
    HST observations. Both are bright elliptical galaxies with a population of
    stars a few billion years old that display no evidence of new star
    In the cases of both GRB150101B and GW170817, the explosion was probably
    viewed 'off-axis', that is, with the jet not pointing directly towards the
    Earth. So far, those events are the only two off-axis short GRBs that
    astronomers have identified. The optical emission from GRB150101B is
    largely in the blue portion of the spectrum, providing an important clue
    that that event is another kilonova, as seen in GW170817. A kilonova is a
    luminous flash of radioactive light that produces large quantities of
    important elements like silver, gold, platinum and uranium. While there are
    many commonalities between GRB150101B and GW170817, there are two very
    important differences. One is their location: GW170817 is relatively close,
    at about 130 million light-years from the Earth, while GRB150101B lies about
    1.7 billion light-years away. The second important difference is that,
    unlike GW170817, gravitational-wave data do not exist for GRB150101B.
    Without that information, the team cannot calculate the masses of the two
    objects that merged. It is possible that the event resulted from the merger
    of a black hole and a neutron star, rather than two neutron stars. It is
    possible that a few mergers like the ones seen in GW170817 and GRB150101B,
    have been detected previously, but were not properly identified using
    complementary observations in different wavelengths of light, according to
    the researchers. Without such detections — in particular, at longer
    wavelengths such as X-rays or optical light — it is very difficult to
    determine the precise location of events that produce gamma-ray bursts. In
    the case of GRB150101B, astronomers at first thought that the event might
    coincide with an X-ray source detected by Swift in the centre of the galaxy.
    The most likely explanation for such a source would be a supermassive black
    hole devouring gas and dust. However, follow-up observations with Chandra
    placed the event further away from the centre of the host galaxy. According
    to the researchers, even if LIGO had been operational in early 2015, it
    would very likely not have detected gravitational waves from GRB150101B
    because of the event's greater distance from the Earth. All the same, every
    new event observed with both LIGO and multiple light-gathering telescopes is
    likely to fit important new pieces into the puzzle.


    A team of astronomers has used the VIMOS instrument on the Very Large
    Telescope (VLT) to identify a gigantic proto-supercluster of galaxies
    forming in the early Universe, just 2.3 billion years after the Big Bang.
    That structure, which the researchers nicknamed Hyperion, is the largest and
    most massive structure to be found so early in the formation of the
    Universe. The enormous mass of the proto-supercluster is calculated to be
    more than 10 to the 15 times that of the Sun. That titanic mass is similar
    to that of the largest structures observed in the Universe today, but
    finding such a massive object in the early Universe surprised astronomers.
    Located in the COSMOS field in the constellation Sextans, Hyperion was
    identified by analyzing the vast amount of data obtained from the VIMOS
    Ultra-deep Survey which provides a 3D map of the distribution of over 10,000
    galaxies in the distant Universe. The team found that Hyperion has a very
    complex structure, containing at least 7 high-density regions connected by
    filaments of galaxies, and its size is comparable to that of nearby super-
    clusters, though it has a very different structure. Superclusters closer to
    the Earth tend to have a much more concentrated distribution of mass, with
    clear structural features. But in Hyperion, the mass is distributed much
    more uniformly in a series of connected blobs, populated by loose associa-
    tions of galaxies. That contrast is most likely due to the fact that nearby
    super-clusters have had billions of years for gravity to gather matter
    together into denser regions — a process that has been acting for far less
    time in the much younger Hyperion. Given its size so early in the history
    of the Universe, Hyperion is expected to evolve into something similar to
    the immense structures in the local Universe such as the superclusters
    making up the Sloan Great Wall or the Virgo Supercluster that contains our
    own galaxy, the Milky Way. Understanding Hyperion and how it compares to
    similar recent structures may give insights into how the Universe developed
    in the past and will evolve into the future, and allow us the opportunity to
    challenge some models of supercluster formation.

    Cornell University

    The Hubble Space Telescope has resumed normal operations after an anxious
    few weeks when it looked as if the stalwart spacecraft was on its last legs.
    Hubble reported itself offline on its Twitter account early in October and
    NASA explained that the craft had entered safe mode after one of the three
    gyroscopes used to point and steady the telescope had failed. According to
    the space agency, the gyro that failed had been “exhibiting end-of-life
    behaviour”, which is no surprise given that Hubble was originally a 15-year
    mission and has now been scanning the Universe for over 28 years. A backup
    enhanced gyro should have seamlessly taken over when the original failed,
    but it initially refused to perform, at a level required for operations,
    after being switched off for 7.5 years. To get it going again, Hubble
    technicians basically instructed the telescope to jiggle around so as to
    shake any blockages out of the gyro, and then switched it off and on again
    and into different modes a few times. That strategy worked, and Hubble
    returned to normal operations on October 26.
    Hubble's life-span is now almost twice what was originally intended, and its
    successor, the James Webb Space Telescope, will be capable of feats that
    Hubble can only dream of. However, the powerful new spacecraft has been
    beset by delays over the last 20 years and its launch date has been
    postponed once again from May 2020 to March 2021. The project has over-run
    its budget many times over and NASA now believes the end total will creep
    over $8bn. If that happens, the agency will have to apply for re-author-
    ization from Congress for the space telescope. That might seem like an
    astronomical sum to pay to further our understanding of the Universe, but
    the James Webb could potentially revolutionize that understanding by making
    observations of the earliest moments after the Big Bang and examining our
    Solar System and nearby exoplanets in detail that has been impossible until
    now. In the meantime, however, scientists are still reliant on booking time
    with observatories like Hubble.


    NASA's Parker Solar Probe is now closer to the Sun than any other spacecraft
    in history, breaking the previous record of 26.6 million miles set by the
    Helios 2 spacecraft in 1976. The probe is now well inside the orbit of
    Mercury. At closest approach, the solar disc will seem 6 times wider than
    it does from the Earth, as the probe is hit by “brutal heat and radiation”.
    Parker's carbon-composite heat shield is expected to heat up to 2000 deg. F.
    The prime mission is to investigate the origin of the solar wind — a project
    best done uncomfortably close to the star. Parker will trace the solar wind
    back to its source and find out how it escapes the Sun's gravity and
    magnetic confinement. The probe's wide-field camera system, WISPR, can
    actually see the solar wind, allowing it to image clouds and shock waves as
    they approach and pass the spacecraft. Other sensors on the spacecraft will
    sample the structures that WISPR sees, making measurements of particles and
    fields that researchers can use to test competing theories. Parker will
    plunge towards the Sun 24 more times in the next 8 years.

    Bulletin compiled by Clive Down
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