Gaia - creating the first 3D census of the Milky Way

10 Dec 2015

At a talk organised by the SCI Cambridge and Great Eastern Group at Cambridge University on 19 November 2015, Prof Gilmore explained how the Gaia Mission will enable a 6-D map of the Milky Way to answer questions such as: How big is the Milky Way? How old is it? How much does it weigh? When did it form? What shape is it? Where are the stars? How fast do they move?.

Image: ‘First Star shines for Gaia’ courtesy of Gaia and ESA

There are roughly 100 thousand million (100,000,000,000) stars in the Milky Way. Today we know to one percent accuracy only seven hundred stars. So we don’t know where stars really are, we don’t know how bright they really are, and we don’t know how they are moving through space.

Gaia, the European Space Agency (ESA) mission to map the Milky Way, is soon to be very big news indeed as early results are made public. Prof Gerry Gilmore FRS, of the Cambridge University Institute of Astronomy is the UK Principle Investigator for Gaia. He has been involved in the project from the very start and, in a riveting lecture, told us of the story of Gaia from funding proposals (1993), through approval (2000), construction, launch (2013) and early data, to the plans for future measurements and increasing public engagement in interpreting and following up Gaia’s findings.

Gaia’s very high precision imaging that delivers 3D positions, 3D motions and chemical elemental abundances for over one billion (1,000,000,000) stars will provide the information required to quantify the formation and evolutionary history of the Milky Way Galaxy. Gaia uses two telescopes to provide absolute positions of stars and will provide one-percent accurate distances for 10 million stars and excitingly good distances for one billion stars. For the first time we will know what stars are like, where they are, and how they are moving.

Astrophysicists will interpret these multi-dimensional data to deduce where and when stars, their planets and the chemical elements were formed, and what else there is in the Milky Way that we cannot see (mostly Dark Matter), and how the Milky Way itself came to form and become what it is today.

The technical achievements involved in the Gaia mission are astonishing: 50 picoradian resolution (equivalent to human hair at 10,000km and 175000 times less than the light-bending effect of the gravity of the sun); the position of Gaia (15,000km distant) must be known to 150m throughout its journey (16 million km over 5 years); and the timing required is so precise that the satellite global timing network has been extended by 10,000 times to picoseconds (a picosecond is the time it takes for light to travel 0.3mm). The changes in position induced by changes in mass of 1 microgram can be detected and must be corrected by release of small amounts of nitrogen gas. Gaia measures the positions of 40 million stars each day, and an analysis of the orbits of those stars reveals details of their larger (bigger than Neptune) orbiting planets.

Huge amounts of data are generated and transferred back to earth - so far more than 15Tb have arrived. The imaging data are processed in Cambridge, where new discoveries are found and published. A programme to involve the public in further investigation of the objects identified by Gaia is underway. The participation of amateur astronomers and schools is encouraged with the incentive not only to participate in new science but also to appear as co-authors on resultant scientific publications.

As if this weren’t impressive enough, Gaia will discover thousands of supernovae and tens of thousands of new planetary systems around other stars, it will monitor hundreds of millions of variable stars and study 500,000 quasars across the Universe, while measuring how space-time is warped by the gravitational fields of the Sun and major planets, and provide our first census of asteroids in the inner Solar System.

We look forward to receiving updates on Gaia from Prof Gilmore in the years to come as the data from this astonishing mission appears. The Gaia mission is planned to continue to 2023... and beyond!

Andrew Howe
Treasurer, SCI Cambridge and Great Eastern Committee

Related Links:

See for more information on the project and videos and for more information about Prof Gilmore and slides from presentations on Gaia.

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