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Gaia is mapping our galaxy and beyond in multi-dimensional detail, completing the most accurate stellar census ever. ̽��ֱ��mission is painting a detailed picture of our place in the Universe, enabling us to better understand the diverse objects within it.

̽��ֱ��mission’s latest data release provides new and improved insights into the space around us. ̽��ֱ��release also brings findings that go far beyond what Gaia was initially designed to discover and digs deep into our cosmic history.

“This focused product data release will open up new insights across astronomy, from the precise orbits of asteroids in our Solar System, to quasar discovery in the distant cosmos,” said Dr Nicholas Walton from Cambridge’s Institute of Astronomy, lead of the UK Gaia Project team and ESA Gaia Science Team member. “It demonstrates the breadth of science enabled by Gaia, and the role of Cambridge and UK Gaia teams in the creation of these data products. This release represents but a small taste of the riches to be revealed with the publication of the next full release, Gaia DR4.”

So – what’s new from Gaia?

Half a million new stars: Gaia's observing mode extended to unlock cluster cores

Gaia’s third data release (DR3) contained data on over 1.8 billion stars, building a pretty complete view of the Milky Way and beyond. However, there remained gaps in our mapping. Gaia had not yet fully explored areas of sky that were especially densely packed with stars, leaving these comparatively unexplored – and overlooking stars shining less brightly than their many neighbours.

are a key example of this. These clusters are some of the oldest objects in the Universe, making them especially valuable to scientists looking at our cosmic past. Unfortunately, their bright cores, chock-full of stars, can overwhelm telescopes attempting to get a clear view. As such, they remain missing pieces in our maps of the Universe.

To patch the gaps in our maps, Gaia selected Omega Centauri, the largest globular cluster that can be seen from Earth. Rather than just focusing on individual stars, as it typically would, Gaia enabled a special mode to truly map a wider patch of sky surrounding the cluster’s core every time the cluster came into view.

“In Omega Centauri, we discovered over half a million new stars Gaia hadn't seen before – from just one cluster!” says lead author Katja Weingrill of the Leibniz-Institute for Astrophysics Potsdam (AIP), Germany, and a member of the Gaia collaboration.

“Through a new use of one of Gaia’s specialised engineering modes, we have been able to generate an imaging catalogue of some of the densest stellar fields in our galaxy,” said Dr Dafydd Wyn Evans, lead of the Gaia photometric development team. “This is enabling us to provide a more complete view of all components of the Milky Way, including the cores of Globular Clusters, some of the oldest structures in our Galaxy.”

This finding not only meets but actually exceeds Gaia’s planned potential. ̽��ֱ��team used an observing mode designed to ensure that all of Gaia’s instruments are running smoothly.

“ ̽��ֱ��Gaia Sky Mapper images required the development of a new processing pipeline to measure the accurate brightness of the hundreds of thousands faint stars not seen by Gaia before,” said Dr Francesca De Angeli, lead of Gaia’s Photometric Data Processing Centre in Cambridge. “This rich data probes regions of the sky previously unseen by Gaia, and fills in important gaps in earlier data releases.”

̽��ֱ��new stars revealed in Omega Centauri mark one of the most crowded regions explored by Gaia so far.

Gaia is currently exploring eight more regions in this way, with the results to be included in Gaia Data Release 4. These data will help astronomers to truly understand what is happening within these cosmic building blocks, a crucial step for scientists aiming to confirm the age of our galaxy, locate its centre, figure out whether it has gone through any past collisions, verify how stars change through their lifetimes, constrain our models of galactic evolution, and ultimately infer the possible age of the Universe itself.

Looking for lenses: Gaia the accidental cosmologist

While Gaia was not designed for cosmology, its new findings peer deep into the distant Universe, hunting for elusive and exciting objects that hold clues to some of humanity’s biggest questions about the cosmos: gravitational lenses.

Gravitational lensing occurs when the image of a faraway object becomes warped by a disturbing mass – a star or galaxy, for instance – sitting between us and the object. This intermediate mass acts as a giant magnifying glass, or lens, that can amplify the brightness of light and cast multiple images of the faraway source onto the sky. These rare configurations hold immense scientific value, revealing clues about the earliest days of the Universe.

̽��ֱ��team identified the candidates from an extensive list of possible quasars (including those from ). Five of the possible lenses are potential Einstein crosses, rare lensed systems with four different image components shaped like a cross. (See .)

Finding lensed quasars is challenging. A lensed system’s constituent images can clump together on the sky in misleading ways, and most are very far away, making them faint and tricky to spot.

Extending Gaia’s value into cosmology brings synergy with , recently launched on its quest to explore the dark Universe. While both focus on different parts of the cosmos – Euclid on mapping billions of galaxies, Gaia on mapping billions of stars – the lensed quasars discovered by Gaia can be used to guide future exploration with Euclid.

Asteroids, stacked starlight and pulsating stars

Other papers published today offer further insight into the space around us, and the diverse and sometimes mysterious objects within it.

One reveals more about 156,823 of the . ̽��ֱ��new dataset pinpoints the positions of these rocky bodies over nearly double the previous timespan, making most of their orbits – based on Gaia observations alone – 20 times more precise. In the future, Gaia DR4 will complete the set and include comets, planetary satellites and double the number of asteroids, improving our knowledge of the small bodies in nearby space.

Another paper maps the disc of the Milky Way by tracing weak signals seen in starlight, faint imprints of the gas and dust that floats between the stars. ̽��ֱ��Gaia team stacked six million spectra to study these signals, forming a dataset of weak features that have never been measured in such a large sample. ̽��ֱ��dataset will hopefully allow scientists to narrow down the source of these signals, which the team suspects to be a complex organic molecule. Knowing more about where this signal comes from helps us to study the physical and chemical processes active throughout our galaxy, and to understand more about the material lying between stars.

Finally, a paper characterises the dynamics of 10,000 pulsating and binary red giant stars in by far the largest such database available to date. These stars were part of a catalogue of two million variable star candidates released in Gaia DR3, and are key when calculating cosmic distances, confirming stellar characteristics, and clarifying how stars evolve throughout the cosmos. ̽��ֱ��new release provides a better understanding of how these stars change over time.

“This data release further demonstrates Gaia’s broad and fundamental value – even on topics it wasn’t initially designed to address,” said Timo Prusti, Project Scientist for Gaia at ESA.

̽��ֱ��next steps

Gaia’s previous Data Release, Gaia DR3, came on 13 June 2022. It was the most detailed survey of the Milky Way to date, and a treasure trove of data on strange ‘starquakes’, asymmetrically moving stars, stellar DNA and more. Gaia DR3 contained new and improved details for almost two billion stars in the Milky Way, and included the largest catalogues of binary stars, thousands of Solar System objects, and – more distantly and outside of our galaxy – millions of galaxies and quasars.

̽��ֱ��mission’s next Data Release, Gaia DR4, is expected not before the end of 2025. It will build upon both Gaia DR3 and this interim focused product release to further improve our understanding of the multi-dimensional Milky Way. It will refine our knowledge of stars’ colours, positions, and movements; resolve variable and multiple star systems; identify and characterise quasars and galaxies; list exoplanet candidates; and more.

Adapted from an ESA press release.