The transient sky as seen by Gaia

Tuesday 16th June, 2015

Our speaker was Dr Elmé Breedt from Warwick University who came to talk to us about "The transient sky as seen by Gaia". She told us that she has been working at the University as a postdoctoral researcher for the past 5 years in their Astronomy Group. She is particularly interested in some of the most compact objects in the Universe from white dwarf stars to black holes.

Dr Breedt began her talk by saying that although the Gaia spacecraft was launched at the end of 2013 she does not expect any of the major science to be published until 2022 as the data is very complicated and tricky to process. She stressed that the Gaia mission, which is an ESA project, would bring about discoveries that are the "next big thing in astronomy".

The main aim of the Gaia mission is to produce a three-dimensional map of the Milky Way and to build on work done by the Hipparcos satellite, which had measured the precise positions of objects in the sky. Hipparcos was also an ESA (European Space Agency) mission and was named after a Greek astronomer, Hipparchus of Nicaea, who applied the branch of mathematics known as trigonometry to astronomy.

Interestingly, the Gaia name used to be capitalized (GAIA) as it was an acronym for Global Astrometric Interferometer for Astrophysics but budgetary constraints meant that the interferometer was dropped in favour of two optical telescopes channelling data to three instruments. The telescopes have ten mirrors between them, which are all shapes and sizes, and these focus the light onto a set of CCDs. These digital detectors make up the largest focal plane ever flown in space — a total of one billion pixels.

Dr Breedt is particularly interested in any cataclysmic variable star systems that Gaia locates. These systems consist of two stars, a white dwarf star and a donor star that gives away its mass to the white dwarf. As the matter from the donor star falls towards the white dwarf a thin turbulent disc, known as an accretion disc, forms which may emit radiation in the form of X-rays or ultraviolet light. Occasionally the material from the disc may fall directly onto the white dwarf leading to a sudden flash of radiation. If enough material builds up on the white dwarf it is possible that it actually becomes unstable and explode as a Type 1a supernova.

As Gaia scans the sky repeatedly over its five-year mission it will map over a billion stars using the parallax method. Dr Breedt is keen to involve the amateur astronomy community. Any astronomers with a telescope and CCD camera can sign up to her mailing list at warwick.ac.uk/ebreedt/gaiamail to receive information about contributing observations to the mission.

Gaia discovered its first supernova (designated Gaia14aaa) last year in September in a galaxy 500 million light years away. Further developments or discoveries can be found on the UK Gaia website: www.gaia.ac.uk or by downloading the Gaia Mission free app for iOS or Android devices. The latest science alerts from Gaia can be found at www.gaia.ac.uk/alerts