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October 2017: Blown Away

October 2017

In the show this time, we talk to Dr Federico Urban about bigravity, graviton and dark matter, Beth Jones rounds up the latest news, and we find out what we can see in the October night sky from Ian Morison and Claire Bretherton.

The News

LIGO-VIRGO announcement of a fourth gravitational wave

On the 27th of September came the announcement of a fourth gravitational wave detection from only two weeks after the VIRGO detector in Italy joined forces with the LIGO detectors. Not only is this the first detection of a gravitational wave with VIRGO, but the first using three different instruments, as the previous three events were found using the two LIGO sites. The signal was picked up at nearly the same time on all detectors, recorded at 10:30 UTC on the 14th of August and named GW170814.This detection is the same type of event as the previous three- a merger of two black holes. Again, the signal gives evidence for intermediate black holes, which are not thought to be able to form through the collapse of massive stars. 1.8billion light years away, two black holes of 25 and 31 times the mass of the sun merged to form a single black hole of 53 solar masses. The missing 3 solar masses was converted to energy, and carried away as gravitational waves, luckily for us.

The addition of the VIRGO detector to the two, LIGO detectors which reside in the US is more important than simply confirming the existence of a gravitational wave. Adding a third detector to the team improves efforts to locate the source of the signal in the sky, shrinking the volume of the universe that is likely to contain it by a factor of 20. GW170814 is currently pinned down to 60 square degrees on the sky, a factor of 10 times smaller than any previous detection. Theres Cassini spacecraft took a final dive towards the planet before being torn apart in the clouds on the 15th September. Launched on the 15th October 1997, the spacecraft carried out pioneering work on uncovering the mysteries of the ringed planet and its many moons. In 2005, Cassini dropped ESAs moon Titan, revealing unsettlingly Earth-like landscapes. In the sky above, Cassini discovered complex organic molecules, the building blocks of life on Earth, in the moon thats a moon! Cassini took stunning images of them all, finding 6 new moons to give Saturn a running total of 62.

Towards Saturn itself, Cassini pinned down the properties of the upper atmosphere, finding it to be mostly hydrogen and 7% helium. The disruptive effects of the moons and smaller moonlets on Saturns rings and atmosphere over the course of 5 months. Even during its final descent, Cassini refused to stop sending back data as it plunged into Saturns temperature, magnetic field and atmospheric conditions.

Although this seems like a cruel fate for poor Cassini, it was the only possible use for the last portion of its fuel reserves. Leaving the satellite to orbit aimlessly could one day result in a collision with one of the moons, dropping off any surviving Earth bacteria with it. With prime candidates for life such as Enceladus and Titan, contamination was too great a risk. In the words of ESAwhile it is certainly sad when a mission ends, it is also a time to celebrate this pioneering journey, which leaves a rich scientific and engineering legacy to pave the way for future missions".

Arecibo Observatory suffers from terrestrial interference

Until the recent construction of FAST in China, Arecibo Observatory in Puerto Rico boasted the largest single aperture radio telescope at a whopping 305m diameter. Made of over 38,000 aluminium panels supported by a mesh of steel cables, the telescope has been active in the Search for Extraterrestrial Intelligence (SETI) and sending out messages visible to other civilizations. In day-to-day operations, the telescope is also used study planets, pulsars, asteroids, galaxies and even dark matter. The sinkholes in Puerto Rico have provided a perfect place to nestle a giant radio telescope.

Unfortunately, Puerto Rico fell in the destructive path of Hurricane Maria last week with the whole island losing electricity in the wake. Much of the population still remain without power or communications as gushing rivers, a dam failure and huge amounts of building damage plague the island. After initial radio silence from the observatory, the staff are now remaining optimistic about the to the telescope. Officials reported that a 29metre line-feed antenna (once used to detect mountains on Venus) fell from a platform about 100m above the dish, puncturing it in several places. A smaller 12m dish was also lost to the storm, knocking about 20 surface tiles loose from the main dish on the way down.

Perhaps most importantly, all staff at the site were reported safe after the storm. The telescope remains un-operational for now ahead of a full assessment of the damage and the repairs required.

Interview with Dr Federico Urban

Dr Federico Urban from KFBI in Tallinn talks about massive bigravity, a recent(ish) theory of gravity that has interesting implications for dark matter. We dip into the origins of bigravity, before touching upon how it could be proved (or disproved).

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during October 2017.

The Planets

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