THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 467 2018 April 22

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    THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 467 2018 April 22

    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


    With little warning, on April 15 a 'Tunguska-class' asteroid flew through
    the Earth–Moon system. 2018 GE3 was discovered just the day before as it
    plunged towards the Sun from the asteroid belt. The asteroid is estimated
    to be 48 to 120 metres in diameter; in all of observational history it is
    the largest known asteroid to pass so close to the Earth.

    International Centre for Radio Astronomy Research

    A telescope in the Western Australia outback has been used to listen to a
    mysterious cigar-shaped object that entered our Solar System late last year.
    The unusual object — known as 'Oumuamua — came from another solar system,
    prompting speculation it could be an alien spacecraft. So astronomers went
    back through observations from the Murchison Widefield Array (MWA) telescope
    to check for radio transmissions coming from the object between the
    frequencies of 72 and 102 MHz — similar to the frequency range in which FM
    radio is broadcast. While they did not find any signs of intelligent life,
    the research helped to expand the search for extra-terrestrial intelligence
    (SETI) from distant stars to objects closer to home. When 'Oumuamua was
    first discovered, astronomers thought it was a comet or an asteroid from
    within the Solar System. But after studying its orbit and discovering its
    long, cylindrical shape, they realised 'Oumuamua was neither, and had come
    from interstellar space. Telescopes around the world observed the visitor
    in an effort to learn as much as possible about it before it headed back out
    of the Solar System, becoming too faint to observe in detail. The MWA is
    located in Western Australia's remote Murchison region, one of the most
    radio-quiet areas on the planet and far from human activity and radio
    interference caused by technology. It is made up of thousands of antennae
    attached to hundreds of 'tiles' that dot the ancient landscape, relentlessly
    observing the heavens day after day, night after night. The research team
    was able to look back through all of the MWA's observations from November,
    December and early January, when 'Oumuamua was between 95 million and 590
    million kilometres from the Earth. They found nothing, but as the first
    object of its class to be discovered, `Oumuamua has given us an interesting
    opportunity to expand the search for extra-terrestrial intelligence from
    traditional targets such as stars and galaxies to objects that are much
    closer. That also allows for searches for transmitters that are many orders
    of magnitude less powerful than those that would be needed to be detectable
    from a planet orbiting even the nearest stars.
    'Oumuamua was first discovered by the Pan-STARRS project at the University
    of Hawaii in October. Its name loosely means 'a messenger that reaches out
    from the distant past' in Hawaiian, and is the first object known to be
    interstellar to pass through our Solar System. Combining observations from
    a host of telescopes, scientists have determined that `Oumuamua is most
    likely a cometary fragment that has lost much of its surface water because
    it was bombarded by cosmic rays on its long journey through interstellar
    space. Researchers have now suggested there could be more than 46 million
    similar interstellar objects crossing the Solar System every year. While
    most of such objects must be too far away to study with current technology,
    future telescopes such as the Square Kilometre Array (SKA) should enable
    scientists to understand more about such interstellar interlopers.

    Columbia University

    A team of astrophysicists has discovered a dozen black holes gathered round
    Sagittarius A* (Sgr A*), the supermassive black hole at the centre of the
    Milky Way Galaxy. The finding is the first to support a decades-old
    prediction, opening up opportunities to understand the Universe better.
    For more than twenty years, researchers have searched unsuccessfully for
    evidence to support a theory that thousands of black holes surround super-
    massive black holes (SMBHs) at the centres of large galaxies. There are
    only about five dozen known black holes in our entire Galaxy — 100,000
    light-years across — and there are supposed to be 10,000 to 20,000 that no
    one has been able to find, in a region just six light-years wide. Sgr A*
    is surrounded by a halo of gas and dust that provides the perfect breeding
    ground for the birth of massive stars, which live, die and could turn into
    black holes there. Additionally, black holes from outside the halo are
    believed to fall under the influence of the SMBH as they lose their energy,
    causing them to be pulled into the vicinity of the SMBH, where they are held
    captive by its force. While most of the trapped black holes remain
    isolated, some capture and bind to a passing star, forming a stellar binary.
    Researchers believe that there is a heavy concentration of such isolated and
    mated black holes in the Galactic Centre, forming a density cusp which gets
    more crowded as distance to the SMBH decreases. In the past, failed
    attempts to find evidence of such a cusp have focused on looking for the
    bright burst of X-ray glow that sometimes occurs in black-hole binaries.
    Astronomers turned to archival data from the Chandra X-ray Observatory to
    test their technique. They searched for X-ray signatures of black-hole–
    low-mass-binaries in their inactive state and were able to find 12 within
    three light-years of Sgr A*. The researchers then analyzed the properties
    and spatial distribution of the identified binary systems and extrapolated
    from their observations that there must be anywhere from 300 to 500 black-
    hole–low-mass-binaries and about 10,000 isolated black holes in the region
    surrounding Sgr A*.


    New data from the MUSE instrument on ESO's Very Large Telescope in Chile
    have revealed a remarkable ring of gas in a system called 1E 0102.2-7219,
    expanding slowly within the depths of numerous other fast-moving filaments
    of gas and dust left behind after a supernova explosion that took place 2000
    years ago in the Small Magellanic Cloud. That discovery allowed astronomers
    to identify for the first time an isolated neutron star with low magnetic
    field located beyond our own Milky Way galaxy. The team noticed that the
    ring was centred on an X-ray source that had been noted years before and
    designated p1. The nature of that source had remained a mystery. In
    particular, it was not clear whether p1 actually lies inside the remnant or
    behind it. It was only when the ring of gas — which includes both neon and
    oxygen — was observed with MUSE that the scientific team noticed that it
    perfectly circled p1. The coincidence was too great, and they realised that
    p1 must lie within the supernova remnant itself. Once p1's location was
    known, the team used existing X-ray observations of it from the Chandra
    X-ray Observatory to determine that it must be an isolated neutron star,
    with a low magnetic field. When massive stars explode as supernovae, they
    leave behind curdled webs of hot gas and dust, known as supernova remnants.
    Those turbulent structures are key to the redistribution of the heavier
    elements — which are cooked up by massive stars as they live and die —
    into the interstellar medium, where they eventually form new stars and
    planets. Typically barely ten kilometres across, yet with masses more than
    our Sun's, isolated neutron stars with low magnetic fields are thought to be
    abundant across the Universe, but they are very hard to find because they
    shine only at X-ray wavelengths. The fact that the confirmation of p1 as an
    isolated neutron star was enabled by optical observations is thus
    particularly exciting.

    NASA/Goddard Space Flight Center

    Astronomers using the Hubble Space Telescope have for the first time
    measured the distance to one of the oldest objects in the Universe, a
    collection of stars born shortly after the Big Bang. That stellar assembly,
    a globular star cluster called NGC 6397, is one of the closest such clusters
    to the Earth. The new measurement sets the cluster's distance at 7,800
    light-years, with just a 3% margin of error. That refined distance
    yardstick provides an independent estimate for the age of the Universe.
    The new measurement may also help astronomers to improve models of stellar
    evolution. Star clusters are the key ingredient in stellar models, because
    the stars in each grouping are at the same distance and have the same age
    and the same chemical composition. They therefore constitute a single
    stellar population to study. Until now, astronomers have estimated the
    distances to our Galaxy's globular clusters by comparing the luminosities
    and colours of stars to theoretical models, and to the luminosities and
    colours of similar stars in the solar neighbourhood. But the accuracy of
    those estimates varies, with uncertainties between 10 and 20%. However,
    the new measurement relies on straightforward trigonometry. Using a novel
    observational technique to measure tiny angles on the sky, astronomers
    managed to stretch Hubble's yardstick beyond the disc of our Milky Way
    The research team calculated NGC 6397's age at 13.4 billion years old.
    The globular clusters are so old that if their ages and distances deduced
    from models are off by a little bit, they can seem to be older than the age
    of the Universe. Accurate distances to globular clusters are used as
    references in stellar models to study the characteristics of young and old
    stellar populations. A model that agrees with the measurements inspires
    some faith in its application to more distant stars. The nearby star
    clusters serve as anchors for the stellar models. Until now, we only had
    accurate distances to the much younger open clusters inside our Galaxy,
    because they are closer to the Earth. By contrast, about 150 globular
    clusters orbit outside our Galaxy's comparatively younger starry disc.
    The Hubble astronomers used the trigonometrical parallax method to obtain
    the cluster's distance. To obtain the distance to NGC 6397, the team
    employed a method to measure accurate distances to pulsating stars called
    Cepheid variables, which serve as reliable distance markers for astronomers
    to calculate accurately the expansion rate of the Universe. With that
    technique, called 'spatial scanning', Hubble's Wide-Field Camera 3 gauged
    the parallaxes of 40 NGC 6397 cluster stars, making measurements every six
    months for two years. The researchers then combined the results to obtain
    the precise distance measurement. They say that they could reach an
    accuracy of 1% if they combine the Hubble distance measurement of NGC 6397
    with the results that are hoped to be obtained from ESA's Gaia space
    observatory, which is measuring the positions and distances of stars with
    unprecedented precision. The data release for the second batch of stars in
    that survey is scheduled for late April.


    Phosphorus is an essential element for life — but new findings suggest that
    it might just have been a matter of luck that there was enough of it for
    life to start on Earth. According to new observations of the Crab Nebula
    (the remnant of a supernova recorded by Chinese astronomers in 1054), the
    abundance and distribution of phosphorus in the Milky Way galaxy may be more
    random than scientists previously thought. As such, some places in the
    galaxy may not have enough phosphorus to support life, even if they are home
    to otherwise hospitable exoplanets. Most of the Universe's phosphorus was
    created during the last gasps of dying massive stars or in supernovae.
    Phosphorus is difficult to observe, and only in 2013 did astronomers make
    the first measurements of the element in a stellar explosion, in the wispy
    remains of the supernova Cassiopeia A. Surprisingly, they found a relative
    abundance of phosphorus up to 100 times greater than is observed in the rest
    of the Milky Way.
    But that might have been an outlier. Recently, astronomers pointed the
    William Herschel Telescope in the Canary Islands towards the Crab Nebula,
    located about 6,500 light-years away. Preliminary data show an amount of
    phosphorus more similar to the values found in the interstellar gas and dust
    of the Milky Way — a pittance compared with the abundance in Cassiopeia A.
    Phosphorus abundances are remarkably variable from one site to another. The
    star that created Cassiopeia A is roughly twice as massive as the one that
    made the Crab Nebula. A more massive star could have generated different
    reactions that produced more phosphorus. The researchers said that if the
    production of phosphorus varies widely across the Galaxy, so might the like-
    lihood of life on other planets. Even if a planet had every other condition
    needed for habitability, it might still be bereft of life because it formed
    where there was a dearth of phosphorus. But the observations are still
    preliminary. The astronomers were able to measure only parts of the nebula
    before clouds and a snowstorm curtailed their observing run. Still, the
    data they do have show significantly less phosphorus in the Crab Nebula than
    in Cassiopeia A. Ultimately, astronomers will need to measure phosphorus in
    other supernova remnants. They really want to look at how it is spreading
    out from supernova remnants and falling back into the interstellar medium.

    DOE/Lawrence Berkeley National Laboratory

    Scientists have decoded faint distortions in the patterns of the Universe's
    earliest light to map huge tube-like structures known as filaments —
    invisible to our eyes — that serve as highways for delivering matter to
    dense hubs such as galaxy clusters. The international scientific team
    analyzed data from past sky surveys using sophisticated image-recognition
    technology to home in on the gravity-based effects that identify the shapes
    of the filaments. They also used models and theories about the filaments
    to help guide and interpret their analysis. The detailed exploration of
    filaments will help researchers to understand better the formation and
    evolution of the cosmic web — the large-scale structure of matter in the
    Universe — including the unseen stuff known as dark matter that seems to
    make up about 85% of the total mass of the Universe. Dark matter constitutes
    the filaments — which researchers learned typically stretch across hundreds
    of millions of light-years — and the so-called haloes that host clusters of
    galaxies are fed by the universal network of filaments. More studies of
    filaments might provide new insights about dark energy, another problematic
    entity that seems to drive the accelerating expansion of the Universe.
    Filament properties could also put gravity theories to the test, including
    Einstein's theory of general relativity, and lend important clues to help
    solve an apparent mismatch in the amount of visible matter predicted to
    exist in the Universe — the 'missing baryon' problem.
    The study used data from the Baryon Oscillation Spectroscopic Survey, or
    BOSS, an Earth-based sky survey that captured light from about 1.5 million
    galaxies to study the Universe's expansion and the patterned distribution of
    matter in the Universe set in motion by the propagation of sound waves, or
    'baryonic acoustic oscillations', rippling in the early Universe. The BOSS
    survey team produced a catalogue of probable filament structures that
    connected clusters of matter that researchers identified in the latest
    study. Researchers also relied on precise, space-based measurements of the
    cosmic microwave background, or CMB, which is the nearly uniform remnant
    signal from the first light of the Universe. While that light signature is
    very similar across the Universe, there are regular fluctuations that have
    been mapped in previous surveys. In the latest study, researchers focused
    on patterned fluctuations in the CMB. They used sophisticated computer
    algorithms to seek out the imprint of filaments from gravity-based
    distortions in the CMB, known as weak lensing effects, that are caused by
    the CMB light passing through matter. Since galaxies live in the densest
    regions of the Universe, the weak lensing signal from the deflection of CMB
    light is strongest from those parts. Dark matter resides in the haloes
    around those galaxies, and was also known to spread from those denser areas
    in filaments. New data from existing experiments, and next-generation sky
    surveys such as the Dark Energy Spectroscopic Instrument (DESI) now under
    construction at Kitt Peak, should provide even more detailed data about the
    filaments. Researchers noted that this important step in sleuthing the
    shapes and locations of filaments should also be useful for focused studies
    that seek to identify what types of gases inhabit the filaments, the
    temperatures of those gases, and the mechanisms for how particles enter and
    move around in the filaments. The study also allows them to determine the
    lengths of filaments.

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