By Alice Guskov, Second Year, Astrophysics
Gaia, which stands for Global Astrometric Interferometer for Astrophysics, has nothing to do with the Greek goddess of the same name. This Gaia is a European space observatory tasked with creating the largest and most precise 3D map of our galaxy.
Launched on December 19 2013, it has two identical telescopes with a common focal plane featuring three science instruments to determine the properties of nearly two billion objects. The astrometric instrument uses parallax to determine the distance of an object as well as its proper motion to find its velocity. The radial velocity spectrometer determines an object’s Doppler shift, and the photometric instrument finds stellar characteristics such as temperature, mass and chemical composition.
After launching, Gaia entered its operational orbit around the Sun-Earth L2 Lagrange point, where the orbital motion is in equilibrium with the gravitational forces, allowing it to hover. L2 is a very popular destination for observational spacecraft because it is behind the Earth, and therefore, observations are not affected by the Earth’s shadow, which can distort images. However, Gaia did not start taking observations as soon as it reached L2. It required four months of calibration and officially started taking measurements on 25 July 2014 - beginning its 11-year mission.
Spinning once every 6 hours, Gaia sends up to 100 gigabytes of data to Earth daily and measures each star an average of 70 times over five years. As you can imagine, this is a lot of data, requiring robust data-handling software. In fact, the University of Bristol’s Astrophysics Group received a grant in 2013 from the UK Space Agency to further develop data-handling software to access the data from the Gaia mission. This software was authored by Dr Mark Taylor, a research fellow and local contributor to the Gaia mission in the School of Physics, who is ‘proud to be contributing to the hundreds of scientists on the Gaia project and [looks] forward to discoveries about the way the Galaxy formed and the properties of the stars that live within it.’
So far, there have been three data releases to the public, with a fourth estimated in 2026 and a final legacy catalogue in 2030. The first data release in 2016 revealed the positions and apparent brightness for 1.1 billion objects. The second release in 2018 expanded upon this data and provided evidence for a past collision with another galaxy, causing the Milky Way’s disc to be curved rather than flat. The third data release in 2022 contained data for over 1.8 billion stars and attempted to patch some of the gaps in previous data. As a result, it identified new star clusters, exoplanets, black holes, quasars and galaxies! I may be biased as an Astrophysics student, but that is incredible. And there is another data release still to come, which will further reveal the intricacies of the universe and continue to revolutionise astronomy.
The Gaia mission was originally meant to last five years, using about a dozen grams of cold gas daily to function. It has greatly exceeded this time frame and is running low on fuel. As a result, it was sent into a ‘retirement orbit’ after switching off its systems around the sun on 27 March 2025. It has been a very emotional moment for everyone who has worked on the mission for the past several years, with the Gaia Mission Manager Uwe Lammers stating, ‘we will never forget Gaia, and Gaia will never forget us.’
Although Gaia will no longer be taking new measurements, this is just the beginning of Gaia’s impact on astrophysics. The huge amount of data it has collected will guide astrophysics for many years to come and possibly lead to many more ground-breaking discoveries.
Featured image: European Space Agency
