The European Space Agency (ESA) is gearing up to launch its newest space telescope, Euclid, which is scheduled to blast off from Cape Canaveral in Florida on 1 July. Euclid is designed to help solve two of the biggest mysteries in the universe: dark energy and dark matter.
These two “dark” components make up more than 95 per cent per cent of the cosmos, but we cannot see them, hence their names, and know very little about what they could be made of. Astronomers infer the existence of dark matter from the behaviour of the matter that we can see, which acts as if there is some extra source of gravity holding everything together. Dark energy has the opposite effect, causing the accelerating expansion of the universe as a whole.
Euclid has two scientific instruments: a visible light camera to measure the shape of galaxies, and a near-infrared detector to measure their brightness and distance. While it isn’t the first space telescope to use either of these types of instruments, it will be unusual in that it is planned to observe a huge swathe of space, cataloguing over a billion galaxies across more than one-third of the sky.
“With Hubble and the James Webb Space Telescope, those are great observatories for looking at very small regions with very high sensitivity, extraordinary detail – but it’s a bit like looking at the sky through a tiny straw,” says Mike Seiffert at NASA’s Jet Propulsion Laboratory in California, a project scientists for Euclid. “With Euclid we’re less interested in the properties of individual galaxies and objects than we are in measuring a few properties of many, many galaxies.”
Researchers will then use these properties to build two types of map of the universe. The first will use a phenomenon called gravitational lensing, in which relatively nearby matter warps and magnifies the light of objects behind it. The way this bends the apparent shapes of distant objects can tell us about the distribution of the nearby matter acting as the lens.
The distortions are usually tiny, but the huge amount of data Euclid is expected to collect during its six-year mission should allow researchers to use gravitational lensing to map out the distribution of matter – including dark matter, which we can’t see any other way – in the universe. Knowing the distribution of dark matter more precisely will help us figure out how it behaves and may present clues as to what it is really made of.
The other type of map uses ripples in the matter distribution of the universe called baryon acoustic oscillations. These ripples first formed as sound waves soon after the big bang, when the cosmos was a hot, roiling soup of particles and radiation. Eventually, that soup cooled and the waves froze in place, remaining as slightly more dense regions where more galaxies tended to form as the universe expanded. Mapping those relic over-densities can be an extraordinarily effective way look into how and why the expansion is accelerating.
“Seeing how those wrinkles in the early universe propagated forward and how dark energy affected that will help us understand the evolution of the universe and, really, how the universe works,” says Seiffert. If all goes smoothly with the launch, Euclid should start unravelling the mysteries of the cosmos soon.