A mission to map the universe unveils star clusters, asteroids, and tricks of gravity

The ESA's Gaia star surveyor marks its 10th birthday this December.
This image shows many looping and overlapping orbits encircling the Sun, all of different colors (to differentiate between asteroids). The center of the image – representing an area within the orbit of Jupiter – is very densely packed with orbits, while the outer edges remain clearer, showing the background plane of the Milky Way.
One of the new papers from the ESA’s Gaia mission reveals more about 156,823 asteroids. This image shows many looping and overlapping orbits encircling the Sun, all of different colors (to differentiate between asteroids). The center of the image – representing an area within the orbit of Jupiter – is very densely packed with orbits, while the outer edges remain clearer, showing the background plane of the Milky Way. ESA/Gaia/DPAC

On October 10, the European Space Agency (ESA) published some interim data from its nearly a decade-long Gaia mission. The data includes half a million new and faint stars in a massive cluster, over 380 possible cosmic lenses, and the position of over 150,000 asteroids within the solar system. 

[Related: See the stars from the Milky Way mapped as a dazzling rainbow.]

Launched in December 2013, Gaia is an astronomical observatory spacecraft with a mission to generate an accurate stellar census, thus mapping our galaxy and beyond. A more detailed picture of Earth’s place in the universe could help us better understand the diverse objects that make up the known universe. 

500,000 new stars and cluster cores

In 2022, Gaia’s third data release (DR3) contained data on over 1.8 billion stars, which built a rather complete view of the Milky Way and beyond. Even with all that data, there were still gaps in the ESA’s mapping. Gaia still hadn’t fully explored areas of the sky that were particularly densely packed with stars, overlooking the stars that shine a little less brightly than their neighbors. 

A key example of this is in globular clusters. These are some of the oldest objects in the known universe and are especially valuable for looking back into our cosmic past. However, their bright cores can sometimes overwhelm telescopes trying to get a clear view. 

Gaia selected Omega Centauri to help fill in the gaps in the stellar map. Omega Centauri is the largest globular cluster that can be seen from Earth and is a good example of one of the galaxy’s more ‘typical’ clusters. Gaia enabled a special mode to truly map a wider patch of sky that is surrounding the cluster’s core whenever 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!” study co-author and astrophysicist from the Leibniz-Institute for Astrophysics Potsdam (AIP) Katja Weingrill said in a statement. “We didn’t expect to ever use it for science, which makes this result even more exciting.”

The data also allowed the team to detect new stars that are too close together to be properly measured.

“With the new data we can study the cluster’s structure, how the constituent stars are distributed, how they’re moving, and more, creating a complete large-scale map of Omega Centauri. It’s using Gaia to its full potential—we’ve deployed this amazing cosmic tool at maximum power,” study co-author and AIP astrophysicist Alexey Mints said in a statement

The half million new stars showed that Omega Centauri is one of the most crowded regions that Gaia has explored so far. 

Currently, Gaia is exploring eight more regions using these same techniques. The scoop from those exploration will be included in Gaia Data Release 4. It should help astronomers truly understand what is happening within these cosmic building blocks and more accurately confirm the age of our galaxy.

Spotting gravitational lenses 

Gravitational lensing happens when the image of a faraway object in space becomes warped by a disturbing mass, such as a galaxy or star, sitting between the observer and the object. The mass in the middle acts like a giant lens that can magnify the brightness of light and cast multiple images of the faraway source onto the sky. 

[Related: Gravitational Lens Splits Supernova’s Light 4 Different Ways.]

“Gaia is a real lens-seeker,” study co-author and Laboratoire d’Astrophysique de Bordeaux astrophysicist Christine Ducourant  said in a statement. “Thanks to Gaia, we’ve found that some of the objects we see aren’t simply stars, even though they look like them.”

Some of the objects here are not ordinary stars, but distant quasars. These quasars are extremely bright, high-energy galaxies powered by black holes. To date, Gaia has found 381 candidates for lensed quasars. This is a “goldmine” for cosmologists, says Ducourant , and the largest set of candidates ever detected at once. 

Detecting lensed quasars is challenging, since a lensed system’s constituent images can clump together on the sky in misleading ways.

“The great thing about Gaia is that it looks everywhere, so we can find lenses without needing to know where to look,” study co-author and Université Côte d’Azur astrophysicist Laurent Galluccio said in a statement. “With this data release, Gaia is the first mission to achieve an all-sky survey of gravitational lenses at high resolution.”

Asteroids and The Milky Way

One of the studies in this data release reveals more about 156,823 asteroids, pinpointing their positions over nearly double the previous timespan. In the fourth Gaia data release, the team plans to complete the set and include comets, planetary satellites, and double the number of asteroids.

[Related: Smashed asteroid surrounded by a ‘cloud’ of boulders.]

Another study maps the disc of the Milky Way by tracing the weak signals seen in starlight, faint imprints of the gas and dust that floats between the stars. The Gaia team stacked six million spectra to study these signals and the data will hopefully allow scientists to finally narrow down the source of these signals.

“This data release further demonstrates Gaia’s broad and fundamental value—even on topics it wasn’t initially designed to address,” study co-author and ESA Project Scientist Timo Prusti said in a statement. “Although its key focus is as a star surveyor, Gaia is exploring everything from the rocky bodies of the solar system to multiply imaged quasars lying billions of light-years away, far beyond the edges of the Milky Way. The mission is providing a truly unique insight into the Universe and the objects within it, and we’re really making the most of its broad, all-sky perspective on the skies around us.”