ESA’s Euclid captures the Milky Way’s crowded coronary heart

For simply at some point, our darkish Universe detective, Euclid, turned its gaze in the direction of the sunshine: the extraordinarily shiny internal area of our Milky Way galaxy, referred to as the galactic bulge. This particular request got here from astronomers who had been after what Euclid does finest: capturing big areas of the sky in crisp element.

Designed to observe billions of faraway galaxies, the area telescope’s seen gentle digital camera is delicate sufficient to inform aside particular person stars in our super-crowded galactic bulge, with out being blinded. This uncommon capacity is essential for what scientists wish to use this picture for: finding out planets round different stars utilizing a particular approach known as microlensing. But earlier than diving into that, let’s first take a more in-depth take a look at this awe-inspiring picture itself.

On 23 March 2025, Euclid captured this huge photograph in nearly 26 hours. It’s a mosaic of 9 ‘pointings’ from its seen gentle digital camera [1], with every pointing overlaying a patch of the sky bigger than the total Moon. 

For comparability, Euclid’s sharpness and sensitivity in seen gentle is just like the NASA/ESA Hubble Space Telescope’s vast discipline digital camera. But every pointing that Euclid captures in a number of hours spans an space 270 instances bigger than Hubble’s discipline of view. To observe the identical Euclid mosaic, the Keck Observatory would want round 2000 hours. Euclid is quicker, and capable of seize particulars from fainter stars that might be in any other case missed when observing from the bottom. This single mosaic additionally encompasses the whole area that the upcoming Roman area telescope will monitor for planet looking.

Euclid captured greater than 60 million stars on this photograph, together with nebulas and star clusters. This crowded area of our galaxy is the proper place for astronomers to seek for exoplanets with microlensing. Text continues after picture slider. 

Finding exoplanets with gravitational microlensing

Microlensing is a type of gravitational lensing. While Euclid principally makes use of lensing to discover large faraway objects, comparable to clusters of galaxies, this new picture of the galactic centre helps scientists to review lenses on the smallest scales – attributable to stars and exoplanets in our personal galaxy. 

Microlensing depends on the possibility alignment of two stars with an observer. As one star crosses in entrance of one other, the nearer star acts like a cosmic magnifying glass, bending and brightening the background star’s gentle. If a planet orbits the nearer star, its gravity additionally bends this gentle, in a barely uneven means. This tiny further change in brightness is how the presence of a planet is revealed.

“To catch microlensing, you need to observe parts of the sky that are crowded with stars, such as close to the centre of our galaxy,” explains Jean-Philippe Beaulieu of the Institut d’Astrophysique de Paris in France, and the University of Tasmania in Australia. Jean-Philippe was the unique instigator of Euclid’s galactic bulge survey, and he co-led the exoplanet working group of the Euclid Consortium.  

“During the last twenty years, almost 300 exoplanets have been discovered using this technique, all with ground-based telescopes and all towards the centre of our galaxy. This image from Euclid includes 51 known planetary systems – and it will assist in studying many more that will be found,” he provides.  

Measuring planet lots with Euclid

To catch a microlensing occasion, a telescope would want to review a star for over twenty days. This is required to see the unevenness of the sunshine being bent, because the planet orbits round its host star. So, in Euclid’s at some point of commentary, no new occasions could be discovered. But what makes this picture so particular is that it permits scientists to measure the mass of planets which are already recognized, in addition to planets which are but to be found.

“In 24 hours, Euclid has already captured the stars involved in all the future microlensing events that the Roman space telescope will detect, but before the stars and planets involved have aligned,” says Natalia Rektsini of the Institut d’Astrophysique de Paris in France, who led the discharge of Euclid’s galactic bulge survey knowledge for the scientific group.

“This means that anyone who detects a microlensing event in the same region, for example with Roman, will be able from now on to use Euclid data as a time reference in the past and see how the stars looked before they overlapped,” Natalia explains. “Since Euclid can clearly separate individual stars, one can then measure how fast they move over time and use that information to confirm the existence of a planet and determine its mass. This would not be possible with data from one point in time.”

Icy planets and extra

With most planet-hunting methods, it’s simpler to search out massive, sizzling planets orbiting large stars. For microlensing that isn’t the case. “This technique is unbiased, we discover whatever is out there,” says Natalia. “It is uniquely suited to discover cold exoplanets. And we expect every star in the Milky Way to host at least one such planet.”

The host stars of two recognized chilly exoplanets seem in Euclid’s knowledge, and each are particular to the workforce.

“I led the team that discovered OGLE-2005-BLG-390Lb 20 years ago,” says Jean-Philippe. “It’s an icy planet, a bit like Hoth from Star Wars. After all this time, I’m excited that Euclid might finally allow us to measure its precise mass.”

“OGLE-2013-BLG-341Lb is a rare and fascinating system,” says Natalia. “It consists of two stars and one planet. By combining earlier observations from Keck and Hubble with new Euclid data, we can finally separate the stars and confirm the planet’s mass.”

“This result shows what a relatively small, dedicated team, can achieve within a large international mission,” says Valeria Pettorino, Euclid Project Scientist at ESA. “The exoplanet team included strong contributions from early-career researchers and was supported by the Science Ground Segment unit working on the visible instrument.”

“In just 24 hours, Euclid has delivered unique data on the Milky Way’s centre, with a large and sharp view of this region. With time, the separation between sources and lenses increases. That’s why this Euclid data will be a time reference for past and future missions and enable studies of exoplanets and their masses. This data can also be used for other scientific applications, from brown dwarfs and binary stars to stellar motions and dust across our galaxy.”

Notes for editors

Explore this image at the highest resolution in ESASky.

More information on how to download the new Euclid data can be found here.  

[1] For the galactic bulge survey, to maintain the observations as secure as attainable solely Euclid’s seen digital camera (VIS) was used. That’s why the unique picture is in black and white. To add color to the photograph for this public launch, knowledge from the ground-based Canada-France-Hawai’i Telescope (CFHT) was added. 

About Euclid

Euclid was launched in July 2023 and started its routine science observations on 14 February 2024. The goal of the mission is to reveal the hidden influence of dark matter and dark energy on the visible Universe. Over a period of six years, Euclid will observe the shapes, distances and motions of billions of galaxies out to 10 billion light-years.

Euclid is a European mission, built and operated by ESA, with contributions from NASA. The Euclid Consortium – consisting of more than 2000 scientists from 300 institutes in 15 European countries, the USA, Canada and Japan – is responsible for providing the scientific instruments and scientific data analysis. ESA selected Thales Alenia Space as prime contractor for the construction of the satellite and its service module, with Airbus Defence and Space chosen to develop the payload module, including the telescope. NASA provided the detectors of the Near-Infrared Spectrometer and Photometer, NISP. Euclid is a medium-class mission in ESA’s Cosmic Vision programme.