• Analysis
Euclid mission data release reveals 900m galaxies and thousands of strong gravitational lensing cases
The European Space Agency's Euclid mission has released its first major batch of data, cataloguing more than 900 million galaxies and about 15,000 potential cases of strong gravitational lensing, a phenomenon that could help unlock the secrets of the dark universe.
A first taste of the largest cosmic map
The European Space Agency's Euclid mission, launched in July 2023, is working towards the largest cosmic map ever made: a survey spanning a third of the sky and more than 10 billion years of cosmic history. Its first major data release has now revealed more than 900 million galaxies.
That haul is only a fraction of what the telescope will gather over its lifetime:
- •The released data covers about 14% of the total sky area Euclid will map.
- •The release also contains more than 60 million potential quasars - blazing objects at the centre of distant galaxies, powered by supermassive black holes.
- •Prof Andy Taylor of the University of Edinburgh, who leads the UK science ground segment for the mission, described the dataset as the biggest high-resolution image of the universe ever produced.
"The technological leap that's Euclid is that we can keep that high resolution, but now we can basically map huge volumes of the sky…"
That quotation, from Taylor, underlines what sets the survey apart: while other projects may cover more sky, he said none matches Euclid's detail and information content, and Hubble offers high resolution only over a smaller area.
Why strong gravitational lensing matters for dark matter
Among the highlights are about 15,000 potential cases of strong gravitational lensing, a phenomenon that could help unlock the secrets of the dark universe. It occurs when one galaxy, often embedded in a galaxy cluster, sits in front of another, more distant galaxy. As Einstein predicted, the foreground galaxy's gravity distorts space-time, bending the light from the background galaxy and producing bright arcs or rings.
The effect is significantly boosted by dark matter, which adds mass and gravitational pull to a galaxy. Because the lensing is influenced by how this mysterious substance is distributed in a galaxy, Taylor said studying it may allow scientists to rule out competing theories about what dark matter actually is.
"With strong gravitational lensing, you find out how the dark matter is clumping and that's very diagnostic of the type of matter that it is."
Those are the words of Stephen Serjeant, professor of astronomy at the Open University, who added that there is a good chance the next breakthrough on the nature of dark matter might come from strong gravitational lensing.
From roughly 1,000 known cases to 15,000
The leap in scale is striking. Experts previously knew of about 1,000 cases of strong gravitational lensing; the Euclid data contains about 15,000 probable cases. By the end of the mission, around 170,000 are expected.
Quasars, weak lensing and what comes next
Dark energy and dark matter are thought to make up about 70% and 25% of the universe respectively, and Euclid's survey is designed to probe both. Alongside strong lensing, the mission will use weak gravitational lensing - the subtle distortion of distant objects by dark matter in the foreground.
"We can use that pattern of distortions to actually make a map of where all the dark matter is in the universe."
Taylor explained that different types of dark matter and dark energy should produce slightly different patterns on the sky, giving the survey a way to distinguish between them. Reading those patterns is no longer something a person can do alone: "No human eyeball is able to look at all of the Euclid data any more. It's now too big."
A further release of Euclid data was expected to land next summer, adding galaxy distribution results and weak gravitational lensing data.
