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Australian Sky & TelescopeAustralian Sky & Telescope

Australian Sky & Telescope October 2018

Australian Sky & Telescope is a world-class magazine about the science and hobby of astronomy.  Combining the formidable worldwide resources of its venerable parent magazine with the talents of the best science writers and photographers in Australia, Australian Sky & Telescope is a magazine produced specifically for the Southern Hemisphere’s astronomers.

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always new things to learn

ONE OF THE GREAT BENEFITS of the scientific way of thinking is that it (mostly) works to keep you humble. That is to say, just when you think a certain phenomenon has been all figured out, something new comes along to pop your bubble. Take the Moon, for example. For many years, there had been three main lunar origin theories, and everyone was relatively content to continue investigating each of them on the understanding that one would prevail. Then the Apollo astronauts brought samples of moonrock back to Earth and the whole situation was turned upside down. The rocks showed that none of those three theories could be correct, and a new one — a cosmic collision — took centre stage. Fine. But even that theory has its problems, and…

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10 new moons for jupiter

ON JULY 17, the International Astronomical Union’s Minor Planet Center announced that a search team led by Scott Sheppard (Carnegie Institution for Science) has identified 10 new moons of Jupiter, bringing the known total to 79 — the most of any planet in our Solar System. Of that total, Sheppard has led the searches that discovered 51 of them. Dozens of Jupiter’s moons circle the planet in a retrograde direction, that is, opposite that of the planet’s spin, in a swarm of distant orbits. They cluster in three groups of 15 to 20 objects, named for members Ananke (discovered in 1951), Carme (1938) and Pasiphae (1908). Most likely each of these moonlet ‘families’ represents fragments of larger precursors that were shattered by collisions early in Jupiter’s history. Of the 10 new finds,…

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organics inside enceladus: complex enough for life?

NASA’S CASSINI made Enceladus, one of Saturn’s icy moons, famous for its plumes of salty, organics-laced water-ice crystals. Now, a closer analysis of data from two spectrometers aboard the spacecraft reveals that the carbon-based brew inside Enceladus must be more massive and complex than previously realised. Scientists had used Cassini’s Ion and Neutral Mass Spectrometer, which can only measure up to 100 atomic mass units, to detect relatively simple organic compounds. For example, methane (CH4 ) has an atomic mass of 16 amu. But in this new study, published in the June 28 issue of the journal Nature, data from the spacecraft’s Cosmic Dust Analyzer (CDA) revealed that Enceladus’s organic complexity extends up to thousands of atomic mass units. Moreover, the CDA researchers, led by Frank Postberg (Heidelberg University, Germany) detected high-mass…

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best long-range test of general relativity

ASTRONOMERS HAVE CONDUCTED the best galaxy-scale test of general relativity yet, and it rules out some (but not all) theories of modified gravity. These theories provide the main alternative to the existence of dark matter. General relativity has passed extensive tests within the confines of our Solar System. But fewer tests exist on scales of thousands or millions of light-years. On larger scales, theories of modified gravity predict that gravity behaves differently than it does in our Solar System. While astronomers have conducted some tests on galactic scales, none of them has put strong limits on modified gravity. Now, a study led by Thomas Collett (University of Portsmouth, UK) has provided such a test. The team investigated Hubble and Very Large Telescope observations of a so-called Einstein ring, where a galaxy’s gravity…

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pulsar test limits the existence of a ‘fifth force’

SCIENTISTS RECENTLY STUDIED a pulsar binary system to constrain the existence of a hypothetical fifth fundamental force of nature. We already know about four fundamental forces: gravity, electromagnetism and the strong and weak nuclear forces. Some scientists attempting to explain anomalous experimental results have speculated about the existence of a fifth force of nature, one that could work on dark matter. Relativity predicts that normal matter should fall freely toward dark matter. But a fifth force that has the ability to interact with both normal and dark matter could strengthen or diminish dark matter’s gravitational pull. Lijing Shao (Max Planck Institute for Radio Astronomy, Germany) and colleagues tested for this effect using the binary system PSR J1713+0747. This pulsar and its white dwarf companion, which are in a relatively wide 68-day orbit, lie…

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destroyed star feeds a black hole’s jet

FOR THE FIRST TIME, astronomers have witnessed the birth and growth of a black hole’s jet, fueled by a star shredded in the black hole’s gravitational field. Such tidal disruption events are thought to fuel jets some 10% of the time, but until now the events have been too far away to see the resulting beams of plasma. In January 2005 Seppo Mattila (University of Turku, Finland) and colleagues spotted an infrared flare near the active black hole of the western galaxy in the galactic pileup Arp 299. By July, a compact radio source had joined it. Over the next decade, this radio source grew and stretched into a clumpy streak. Material in the jet at first moved at almost the speed of light, then slowed down to a mere 22%…