Developments in Gravitation and Cosmology - Professor Bob Lambourne, Open University

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Not since Galileo in 1610 made his ground-breaking discoveries using the newly invented telescope, have we been at such a scientific threshold - a new age of astronomy. Such was the view of our Vice-President, Professor Bob Lambourne, in his February 2018 lecture to our Society. For not only were gravity waves, originating from two colliding neutron stars 130 million light years away, detected on 17th August 2017 (GW170817) by the LIGO interferometers in Hanford and Livingston, and the Virgo interferometer near Pisa, but also parallel observations were made all across the electromagnetic spectrum.

Professor Lambourne started his lecture reprising material he had presented to the Society in February last year: Newtonian –v– Einsteinian theories of gravity, Interferometry and LIGO, a brief history of the universe. He then went on to describe the discovery timeline of that neutron star collision detection on 17th August last year.

1.7 seconds after the gravity wave event, a gamma ray burst was detected by the NASA/DoE Fermi space telescope. 6 minutes later the Virgo observatory confirmed the LIGO data (it had taken time because the Virgo detection was very weak, being close to one of the instrument’s blind spots). 40 minutes after the event, the gravity wave alert was sent out to the astronomical community. 5 hours later Virgo and LIGO data were combined to determine the source direction of the original neutron star collision – somewhere near the elliptical galaxy NGC4993 near γ-Hydra. Now optical telescopes could get to work and after 11 hours the Swope 1-metre telescope spotted the collision – the galaxy’s red shift (z = 0.009) put it at a distance of 130 million light years mirroring the gravitational wave data. 15 hours after the event, the Swift satellite reported a bright UV emission. 2 weeks later there was X-ray data. Interestingly, but rather disappointingly, the Ice Cube Neutrino Detector at the South Pole failed to detect anything.

All this takes place rather fittingly almost exactly a century after the birth of modern Cosmology; it heralds the birth of multi-messenger astronomy and hopefully will give us new insights to things like gamma-ray bursts, binary star evolution, heavy element synthesis – and, who knows, even dark matter! “There is a huge revolution in progress” Professor Lambourne concluded “This is a great time to be interested in astronomy”.

Sandy Giles

Variable Star Research using SuperWASP - Prof Andrew Norton, Open University

Professor Andrew Norton and WAS' DR Sandy Giles

Professor Andrew Norton and WAS' DR Sandy Giles

Prof Norton and his colleagues certainly took advantage of the data harvested by SuperWASP telescopes when advancing our knowledge of variable stars. The Wide Angle Search for Planets (WASP) is an international consortium of several academic organisations primarily performing an ultra-wide angle search for exoplanets using transit photometry. Two continuously operating observatories in the Canary Islands and South Africa cover the Northern and Southern Hemispheres, and simultaneously monitor many millions of stars at magnitudes 8 to 15 using eight wide-angle cameras.

SuperWASP

SuperWASP

(The telescopes are about fifteen years old now and Prof Norton amused us with the story that in the early days, while trying to eke out their research budget, they were compelled to buy the Canon 200 mm f1.8 lenses in just one’s and two’s. Unfortunately Canon stopped making them before the two telescopes were completed and all remaining stocks were bought up by a single buyer who put them up on e-Bay for sale. Fortunately they were able to persuade the university’s Purchasing Department to bid for them and hence complete the instruments!)

So though the primary aim of WASP was to monitor stars for exoplanets, there was a wealth of other data which could be put to good use on variable stars. And we’re talking big data here! Using a Linux computer cluster, initially 30 million stars were identified with apparent periods of variation. Then, using specially written software to automatically filter out unwanted interferences, 771,000 stars were found to have valid periods. And out of this work emerged a number of discoveries.

For example, 143 short period eclipsing binaries with periods of less than 5½ hours were discovered – only 12 were known previously. And the orbital period of many binary stars varies, which may be caused by the presence of a third massive body in the system. They studied the period variations in 13,927 eclipsing binary candidates and observed sinusoidal period changes, strongly suggestive of third bodies, in 2% of cases; however, linear period changes were observed in a further 22% of systems, likely to reflect longer-term sinusoidal period variations caused by third bodies. But this is only scratching the surface of how stars are organised. One binary pair turned out to be a doubly eclipsing quintuple low-mass star system, with a group of three stars orbiting another group of two!

So just as we are now discovering that planets associated with stars are in fact commonplace, it now seems single stars are in a minority, especially at higher masses. And the notion that binary stars have planets is not far-fetched either.

Much to ponder after this technical but, judging by the large number of questions asked, very engaging lecture.

Sandy