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November 2017: Under New Skies

November 2017

... and under new management, but still not on time! In the show this time, we talk to Dr. Premana Premadi, Dr. Hesti Wulandari, Dr. Taufiq Hidayat and Dr. Mahasena Putra about recent highlights in Indonesian astronomy, Josh Hayes rounds up the latest news, and we find out what we can see in the November night sky from Ian Morison and Claire Bretherton.

The News

This month in the news: Cassini; gone but not forgotten, the possible discovery of an exomoon and major results from LIGO.

Not content with being the subject of this year's Nobel Prize for Physics, gravitational waves are once again sending ripples through the scientific community. On the 16th of October, the gravitational wave observatories LIGO and Virgo announced that not only have they detected gravitational waves from two merging neutron stars, but electromagnetic counterparts to the merger were also detected, right across the spectrum. General relativity predicts that gravitational waves are something produced by objects accelerating, and the more massive the object, the bigger the wave. Since neutron stars are so massive, the gravitational waves produced by two of them merging are large enough for us to detect. Gravitational waves were first observed in September 2015, but the detection of EM waves from the same source has caused a huge amount of excitement. The first detection was made by the Fermi Gamma-ray Space Telescope, which detected a gamma ray flash made 2 seconds after the merger. The nature of this burst is incredibly similar to short gamma-ray bursts, which have long been thought to be made by neutron star mergers, but until today we have had no proof of that. Follow up observations are now going to be possible due to the localisation of the burst, made possible by collaboration between LIGO and Virgo, who together are able to localise any gravitational wave detection to about 30 square degrees. This is going to open the door to new tests of GR and the origins and nature of astrophysical phenomena we have long wondered about.

Despite crashing into Saturn on the 17th of September, Cassini is still making waves, of a non-gravitational kind. Scientist examining data from the final few months of the mission have released some of their findings, many of which the community have found surprising. Cassini spent the last 4 months of its 20 year mission repeatedly diving between Saturn and its rings, before being steered onto a collision course with the planet. By plunging into the atmosphere, Cassini was able to collect information on the composition of the planet's atmosphere, as well as its gravitational and magnetic fields. The magnetic fields have been especially surprising. It is thought that in order to generate a magnetic field through rotation of its core, a theory known as dynamo theory, a planet must have a misalignment of around 10 degrees between its rotation and magnetic field axes. Saturn has been found to have a misalignment of less than 0.06 degrees. Current theory suggests that for such good alignment, the magnetic fields should have died away within 100 million years. As this hasn't happened, scientists need to reevaluate their understanding of dynamo theory. Through the measurements of the rotation, we have also been given the best estimate of the length of a day on Saturn, which has been found to be about 10.8 hours.Cassini entered the atmosphere at a higher altitude than expected, as it was discovered that the atmosphere extends almost all the way out to the rings. Within the atmosphere, scientists were expecting to find evidence of ring material falling to the surface. This would have been reflected in high measurements of water, as the rings have a high quantity of ice within them. However, Cassini instead measured high concentrations of methane, a gas which was not at all expected to exist in the rings or upper atmosphere. This has puzzled everyone involved and the jury is still out on what leads to such abundances of a gas that is supposed to not be able to last long in such environments due to its volatility.

In the first detection of its kind, the Kepler Space Telescope has possibly found a signal from an exomoon, and now the first explorations of the nature of the moon have been released. In July, David Kipping and Alex Teachey made the announcement that within Kepler data they had discovered the signs of a giant exomoon orbiting the planet Kepler-1625b. The planet is a gas giant, somewhere in size between Saturn and a brown dwarf. At this point, it is important to note that the exomoon has not been confirmed, as the Kepler data on the planet and the exomoon is not of high enough quality, though the Hubble Space Telescope conducted observations on the 29th of October to attempt to confirm its existence. Due to the lack of data, it is difficult to characterise the exomoon, but that hasn't stopped people from trying. In a paper accepted by the Astronomical Journal on the 14th of October (available on the arXiv pre-print server), Rene Heller has published his analysis of what data there is. The bottom line is that whilst the exact mass and size of the moon is unknown, the bounds on these parameters mean that the moon could be anything between an Earth-mass gas planet to a Saturn sized rocky world. Heller's analysis points towards something somewhere in the middle, likely a Neptune-mass exomoon. This is an incredible find, as all current planetary formation theories cannot explain how such a large moon would form. There are currently three understood methods for a planet to acquire a moon. The first is through impact, such as our own moon - our planet was hit by a very large object, throwing out material which collapsed to form our moon. The second method is for the moons to form with the planet out of the protoplanetary disk. This is how Jupiter's Galilean moons formed. And the final method is for the planet to capture a pre-formed body with its gravitational field. This method explains the retrograde orbit of Neptune's moon Triton. None of these theories even come close to explaining how such a large moon has come to be around. To quote Heller: if this can be validated as orbiting a super-Jovian planet, then it will pose an exquisite riddle for formation theorists to solve!

Interview with Dr. Premana Premadi, Dr. Hesti Wulandari, Dr. Taufiq Hidayat and Dr. Mahasena Putra

Tom Scragg interviews not one but four visiting speakers from the Institut Teknologi Bandung in Indonesia with a diverse set of research interests, from estimating cosmological parameters, through probing the atmosphere of Titan to helping religious leaders spot the crescent moon in daytime observing conditions.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the Northern Hemisphere night sky during November 2017.

The Planets

Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the Southern Hemisphere night sky during November 2017.

Kia ora and welcome to the November Jodcast from Space Place at Carter Observatory in Wellington, New Zealand.

The Planets

Constellations

Wishing you clear skies from the team here at Space Place at Carter Observatory.

Odds and Ends

When you see a news article titled "the Universe shouldn't exist, scientists say" (see for example here and here), you might be a little concerned. We talk about the Nature paper that these headlines originated from, which tries to pin down a reason for the matter-antimatter asymmetry that we see in the Universe. Why do we see an excess of matter, when antimatter should have been created in equal amounts in the big bang (leading to the subsequent annihilation of both)? The scientists in question tried to see if the antiproton's magnetic moment was to blame for the asymmetry, but to one part per billion it is consistent with its matter counterpart.

Recent analysis of data from the Cassini probe suggests that Saturn's A ring may be confined by several of its satellites - Pan, Atlas, Prometheus, Pandora, Janus, Epimetheus, and Mimas - rather than Janus alone as previously thought. Planetary rings, like all astrophysical discs, tend to spread out in the radial direction when the inner particles exchange angular momentum with the outer ones. This means the inner particles lose energy and move inwards, whereas the outer particles gain energy and move outwards, causing the disc to spread out. Moons can counteract this effect due to their gravity, neatly sweeping the disc back together by forming density waves in them. These density waves give rise to the appearance of structures similar to the grooves on a vinyl record. The presence of multiple moons mean they maintain resonances (one moon completes X orbits whilst another completes Y), and this causes distinct patterns of grooves in the planetary disc.

News comes in that Stephen Hawking's thesis "Properties of Expanding Universes" has been made available on the CUP. It was so popular that the Cambridge University website crashed as reported in the Guardian. It was written in 1966 and concerned cosmology and also gravitational radiation/waves in an expanding universe. Almost 60,000 downloads were made in 24 hours, leading to the problems in the website. Prof. Hawking is most renowned for his work on black holes and the theory of Hawking radiation.

Show Credits

News:Josh Hayes
Interview:Dr. Premana Premadi, Dr. Hesti Wulandari, Dr. Taufiq Hidayat and Dr. Mahasena Putra and Tom Scragg
Night sky:Ian Morison and Claire Bretherton
Presenters:Luke Hart, Emma Alexander, Crispin Agar
Editors:Naomi Asabre Frimpong, Andreea Dogaru, Luke Hart, Jake Morgan
Segment Voice:Iain McDonald
Website:Jake Morgan and Stuart Lowe
Producer:Jake Morgan
Cover art:A red sky, as recently brought to the UK by Storm Ophelia. CREDIT: RM Bulseco, via Wikimedia Commons

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