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August 2013: Cataclysm

August 2013

In the show this time, we talk to Dan Thornton about Fast Radio Bursts, Stuart rounds up the latest news and we find out what we can see in the August night sky from Ian Morison and John Field.

The News

In the news this month: discs of dust and galactic winds.

Interview with Dan Thornton

Dan Thornton, a PhD student at the Jodrell Bank Centre for Astrophysics and fellow Jodcaster, tells us about Fast Radio Bursts (FRBs). He explains that FRBs are very narrow single pulses of radio waves a few milliseconds in duration, and tells us about the High Time Resolution Universe radio survey on the Parkes telescope, the survey in which they were found. Although there are several theories of their formation, there is not much evidence to constrain their properties - but they are probably cataclysmic events. To date, no optical or gamma-ray counterparts have been found. These FRBs were found at 'cosmologically significant' distances - looking about halfway back to the time of the Big Bang - and Dan goes on to describe how the distances are measured using the dispersion measure. Dan also tells us about the future and follow-up work on these FRBs, looking at identifying counterparts at other frequencies and the work on automatic identification. Further information about FRBs can be found here.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during August 2013.

In the evening, the stars Vega, Deneb and Altair, in the constellations of Lyra, Cygnus and Aquila, make up the Summer Triangle in the southern sky. About a third of the way up from Altair towards Vega, the asterism of the Coathanger lies in the dark Cygnus Rift. The Ring Nebula, in Lyra, and the Dumbbell Nebula, in Vulpecula, are nice lanetary nebulae that can be viewed in binoculars in this part of the sky. Pegasus and Andromeda rise as the night moves on, the latter containing the galaxy M31. Cassiopeia and Ursa Major are high overhead, near, as always, to the North Star.

The Planets


Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during August 2013.

After sunset, the planets Venus and Saturn, along with the constellations of Virgo and Corvus, can be seen in the west. Venus is a brilliant 'star' near the western horizon, while Saturn is much higher and appears yellow. Small telescopes reveal Saturn's rings and largest moon, Titan, while larger ones show faint banding in the planet's atmosphere and variations in the colour of the rings. Jupiter is in the morning sky, along with Mars and, at the beginning of the month, Mercury. The two brightest stars in the sky after sunset are Spica, in Virgo, and Arcturus, in Boötes the Herdsman. Epsilon Boötis is a lovely double star, consisting of a yellow giant primary star and a bluish-white companion, also known as Pulcherrima - 'most beautiful'.

August sees the Milky Way stretching from east to west across the evening sky, and it contains most of the brightest stars in our night sky. In the north, Vega is to the left of the Milky Way, while Canopus is to the south. Alpha Centauri and Beta Centauri are in the south-west after sunset and point towards the Southern Cross, the smallest of the 88 official constellations. The winter constellation of Scorpius sits high overhead, with the orange star Antares marking the Scorpion's heart and a curve of stars forming its body. Following Scorpius is Sagittarius the Archer, another zodiacal constellation.

Away from the Milky Way, the density of stars drops off rapidly. About halfway above the southern horizon in the evening is Tucana the Toucan. Alpha Tucanae has a magnitude of +2.8, while Beta Tucanae is a loosely bound group of six stars and Kappa Tucanae is a system of two pairs of binary stars. Tucana contains the dwarf galaxy known as the Small Magellanic Cloud (SMC) and the second-brightest globular cluster in our sky, 47 Tucanae. The SMC appears as a cloudy smudge to the unaided eye, and contains several hundred million stars some 200,000 light-years away. With binoculars or a small telescope, star clusters can be seen in and around the SMC. The fuzzy blob of 47 Tucanae sits alongside the SMC, and is a globular cluster of millions of stars within our own galaxy. A stunning sight through binoculars or a telescope, professional telescopes have spent long hours examining 47 Tucanae, but have so far found no planets orbiting its stars. This may be due to the low metallicity of the stars, but the absence of gas giants is still puzzling. The brightest globular cluster in the sky, Omega Centauri, is also well placed for viewing, appearing to the naked eye as a fuzzy star in the north. Over the night, the Southern Cross and the Pointer Stars turn about a point called the South Celestial Pole. This point would appear directly overhead if you were at the South Pole, and all the stars in the southern sky appear to circle around it as the Earth rotates.


Odds and Ends

The Atacama Large Millimeter/submillimeter Array (ALMA) announced in the middle of July that astronomers had used the telescope to detect carbon monoxide (CO) ice around TW Hydrae, a protostellar object at a distance of 175 light-years from Earth. This is the first time that astronomers have seen a "snow line" around another star. The astronomers did not actually find the ice by looking at the CO itself because CO can be found in gas form around many stars and in the interstellar medium. Instead, they determined that ice was present by detecting diazenylium (N2H+), an ion that is easily destroyed when mixed with CO gas but that can exist in solid CO. This result is very important for understanding how planets form around other stars and for understanding how organic chemicals can be created in protostellar discs.

Scientists at the Albert Einstein Institute in Postsdam have been carrying out numerical simulations on neutron star mergers and, for the first time, have seen instabilities which would lead to the formation of giant magnetic fields and some of the most energetic explosions that the Universe has ever seen. When two neutron stars in a binary system merge, they collapse into a black hole and the one-second-long gamma-ray burst they emit as a result of this contains the same amount of energy as our galaxy emits in a year. It is now believed that such high energy levels can be achieved via "magetorotational instabilities" - in other words, turbulence within the colliding plasmas of the neutron stars which would result in enormous magnetic fields, thus fuelling these highly energetic gamma-ray bursts.

A 24-hour observation of Comet ISON using NASA's infra-red Spitzer Telescope has revealed gas and dust flowing from the icy body in a coma 300,000 kilometres long. 1,000 tonnes of what is probably carbon dioxide, along with 50,000 tonnes of dust grains, is being ejected per day as the comet approaches the Sun. ISON will shortly get close enough to melt water ice, and will make a closest approach to the Sun of 1.16 million kilometres on the 28th of November - an encounter which it may or may not survive. Observers will have to wait some time longer to find out whether the comet will become bright enough to be seen with the naked eye from Earth.

Show Credits

News:Stuart Harper
Interview:Christina Smith and Dan Thornton
Night sky:Ian Morison and John Field
Presenters:George Bendo, Mel Irfan and Mark Purver
Editors:Adam Avison, George Bendo, Mark Purver and Christina Smith
Segment Voice:Mike Peel
Website:Mark Purver and Stuart Lowe
Producer:Mark Purver
Cover art:Composite image of the Parkes Radio Telescope and a radio map of the Milky Way, with an artist's depiction of a Fast Radio Burst coming from outside our Galaxy. CREDIT: CSIRO/Harvard/Swinburne Astronomy Productions

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