Last starlight for space telescope Gaia
ESA’s space telescope Gaia, which maps the Milky Way, completes its active phase of scanning the sky on 15 January. Over the past decade, Gaia has made more than three trillion observations of about two billion stars and other cosmic objects. ‘Gaia is already the discovery machine of the decade,’ Leiden astronomer Anthony Brown says of the retired telescope.
Gaia was launched on 19 December 2013, and its fuel tank is now nearly empty. The spacecraft uses about a dozen grams of cold gas per day to rotate with extreme precision and scan the sky. However, this is far from the end of the mission. Technology tests are planned for the coming weeks before Gaia is moved to its ‘retirement’ orbit. Two major data releases are also scheduled around 2026 and the end of this decade.
‘This marks the end of scientific observations for this fantastic mission, which has exceeded all our expectations and lasted almost twice as long as originally planned,’ says ESA Science Director Carole Mundell. ‘The wealth of data Gaia has collected provides unique insights into the origin and evolution of our Milky Way and the astrophysics of our solar system. The unique astrometry insights will leave a legacy for future generations.’
‘After 11 years in space, and surviving micrometeorite impacts and solar storms, Gaia has finished collecting scientific data. Now, all eyes are on preparing the next datasets,’ says Gaia Principal Scientist Johannes Sahlmann. ‘I’m excited about the discoveries that still await us.’
Gaia delivers the best Milky Way map ever
Gaia has mapped the positions, distances, movements, brightness, composition, and many other characteristics of stars over the years with its three instruments. This has already allowed Gaia to achieve its primary goal: building the largest, most precise map of the Milky Way, showing our galaxy like never before.
Gaia has also created the best-reconstructed image of our galaxy from an external perspective. The newly released artistic impression of the Milky Way is based on Gaia data from numerous scientific papers published over the past decade.
‘It contains significant changes compared to earlier models because Gaia has transformed our view of the Milky Way. Even basic ideas have been revised, such as the rotation of the central bar of our galaxy, the warp of the disc, and the detailed structure of spiral arms and interstellar dust near the Sun,’ says Stefan Payne-Wardenaar, a scientific visualisation expert at the Max Planck Institute for Astronomy in Germany.
Discovery machine of the decade
Gaia's repeated measurements of distances, movements, and characteristics of stars enable ‘galactic archaeology’ of the Milky Way. The discovery of missing links in the complex history of our galaxy helps astronomers learn more about our origins.
From detecting ‘ghosts’ of other galaxies and multiple streams of ancient stars merged with the Milky Way in its early history, to finding evidence of an ongoing collision with the Sagittarius dwarf galaxy, Gaia is rewriting the Milky Way's history and making predictions about its future.
While scanning the stars in our galaxy, Gaia has also spotted other objects, from asteroids in our solar system to galaxies and quasars (the bright and active centres of galaxies powered by supermassive black holes) outside the Milky Way. For example, Gaia has mapped the precise orbits of more than 150,000 asteroids. The space telescope has also created the largest 3D map of approximately 1.3 million quasars, some of which date back to when the universe was only 1.5 billion years old.
Gaia has also discovered a new type of black hole, including one with a mass nearly 33 times that of the Sun, hidden in the Aquila constellation, less than 2,000 light-years from Earth. This is the first time such a massive black hole, formed after the collapse of a star, has been detected in the Milky Way.
‘It’s impressive that these discoveries are based only on the first few years of Gaia data and were only recently made. Gaia is already the discovery machine of the decade, a trend that will undoubtedly continue,’ says Anthony Brown (Chair of the Gaia Data Analysis and Processing Consortium (DPAC) and Leiden Observatory).
More discoveries to come
Gaia’s scientific and technical teams are already working at full capacity on preparations for Gaia Data Release 4 (DR4), a dataset expected in 2026. With each release, the volume and quality of data improve, and Gaia DR4, expected to contain 500 TB of data products, is no exception. This dataset will cover the first 5.5 years of the mission, matching its originally planned duration. Gaia DR4 will expand the catalogue of binary stars, already the largest ever. Gaia’s unique ability to detect the subtle motions of closely orbiting celestial pairs has previously revealed hidden companions around bright stars.
Gaia’s last targeted observation took place on 10 January, focusing on the binary star 61 Cygni. This iconic star attracted the attention of 19th-century astronomers, providing some of the first correct measurements of motion and parallax based on a similar technique that Gaia used for about two billion stars.
It is expected that Gaia’s upcoming datasets will also include more exoplanets. This is thanks to the longer observation timespan, making it much easier to spot stars gently ‘wobbling’ due to orbiting planets.
Preparations for the fifth and final major data release at the end of this decade, covering the full 10.5 years of mission data, will begin in the coming months.
Gaia’s retirement plan
After the end of scientific observations, a short period of technology testing begins. These tests have the potential to further improve Gaia’s calibrations and gain insights into the behaviour of certain instruments after a decade in space. This could aid the design of future space missions. After a few weeks of testing, the telescope will leave its current orbit around Lagrange Point 2, located 1.5 million km from Earth in the Sun’s opposite direction. Gaia will then be placed in a heliocentric orbit, far from Earth’s sphere of influence. The spacecraft will enter passive mode on 27 March 2025, to prevent damage or interference with other spacecraft.
Final farewell for space telescope Gaia
During the technology tests, Gaia’s orientation will change, temporarily making the space telescope brighter and visible to small telescopes, though it will remain invisible to the naked eye. A guide is available for locating Gaia in the sky, and amateur astronomers are invited to share their observations.
This article appeared as a press release on astronomie.nl
Header Image: This is a new artistic impression of the Milky Way, based on data from ESA’s Gaia space telescope. Gaia has transformed our view of the Milky Way. Once all the observations Gaia has made over the past ten years are available in two new data versions, we can expect an even sharper image of the Milky Way. Credit: ESA/Gaia/DPAC, Stefan Payne-Wardenaar