Astronomers are predicting an “avalanche of discoveries” after the first major release of observations from a European space telescope built to study the mysterious dark matter and dark energy that comprise the bulk of the universe.
The European Space Agency’s Euclid mission has captured images of 26m galaxies, covering 10bn years of cosmic history. They give researchers unprecedented insight into the forces that shape the cosmos and the galaxies it holds.
The first batch of survey data has allowed researchers to create a detailed catalogue of 380,000 galaxies, revealing the rich variation in galactic structures, with some caught in the act of merging with their neighbours.
Further images reveal how massive galaxies surrounded by dark matter, the invisible substance said to pervade the universe, warp space and magnify more distant galaxies behind them. These rare images are among the best leads scientists have for understanding the nature of dark matter.
Prof Adam Amara, the UK Space Agency’s chief scientist and one of the researchers who first proposed the mission 20 years ago, said it was a “huge relief” to see the observations. “All of the science we designed it for is starting to roll out exactly and even better than we would have hoped,” he said. “I’m convinced there’s groundbreaking science in there, and a lot of it.”
Three years before publishing his general theory of relativity in 1915, Albert Einstein predicted that strong gravitational fields generated by massive objects such as galaxies would warp space-time. Astronomers call the effect gravitational lensing, because the warping behaves like a lens, magnifying more distant objects.
Observations from Euclid gathered over a single week captured 500 strong gravitational lensing events where the warping of space-time is clearly visible. When a background galaxy is magnified by lensing it often appears as a bright arc around the border of the foreground galaxy.
Precise measurements of these bright arcs can reveal how much dark matter lurks around a galaxy. Meanwhile, the clumpiness of the dark matter haloes can shed light on its temperature and potential constituent particles.
“We have precious few clues as to what dark matter is,” said Stephen Serjeant, a professor of astronomy at the Open University. “But one of the ways we might figure out what dark matter is, is how it clumps.” The rarest, but most valuable images have a foreground galaxy that bends light from multiple galaxies behind it. With Euclid, researchers hope to massively increase the number of such images.
“This is the significance of our strong gravitational lenses,” said Serjeant. “It’s the start of an avalanche of new discoveries, and among this avalanche will be beautiful clues about what dark matter is made of.”
The most popular theory of the universe suggests only 5% is made from ordinary matter. Dark matter, an invisible substance that forms what is called the cosmic web, is said to account for 25%. The bulk, about 70%, is said to be dark energy, a mysterious force that is accelerating the expansion of the universe.
Euclid is expected to capture images of more than 1.5bn galaxies over six years. Detailed measurements of these will reveal how dark energy is driving the expansion of the universe. But researchers are also hoping for glimpses of the unknown.
Amara said: “I’m now convinced that we have the image quality in the resolution that in six years’ time, there’ll be new categories of objects discovered by Euclid.”
