Space mission expected to solve ‘missing’ case

Astronomers when they look at the universe can see things – stars, planets and galaxies, which are actually 4 percent of what’s out there. The rest, a staggering 96 percent, is made up of something invisible, the nature of which scientists can only speculate about.

In 2022, the Euclid mission of the European Space Agency (ESA) will set out to search for the elusive missing matter of the universe.

Scientists have known that most of the mass of the universe was missing since the 1930s. It was then that the Swiss-American astronomer Fritz Zwicky made the startling discovery that the observed mass of all the stars in a group of galaxies called the coma contained only 1 percent of the mass he calculated was necessary to produce a sufficient gravitational pull. . To keep the cluster together.

The question of the missing mass boiled over for decades until its presence was further confirmed – in a similar fashion – in the 1970s when Vera Rubin and W. Kent Ford, two American astronomers, observed that a specific galaxy appeared within The mass of the giving stars was only about 10 percent of what was needed for these stars to orbit around the center of the Milky Way. The missing matter was nowhere to be seen, so it was called “dark matter”.

Experimental physicist Professor Peter Cole of Maynooth University, who has served as a cosmologist since 1985, says the idea of ​​how dark matter formed at that time has largely remained the same. “It was a kind of neutral particle that didn’t imagine anything like interacting with other matter. It just aided in the process of gravitational instability. That’s why it was called cold dark matter,” he adds.

In the 1990s, the Cosmic Microwave Background (CMB) was discovered – the radiation from the Big Bang that permeates the universe. Then, in 1998, there was a cosmological bombshell, when American astrophysicist Saul Perlmutter, who set out to find out how slow the expansion of the universe had been since the Big Bang, found that it was accelerating.

The accelerated expansion of the universe appeared in reverse: a bit like asking scientists to accept the motion of a tennis ball would accelerate endlessly after being hit by a racket. To combat this, scientists theorized that an invisible energy was driving the process. He called it dark energy.

The new need to accommodate dark energy meant that estimates of the amount of dark matter had to be revised significantly downwards. The new estimate, which still holds, is that the universe is made up of 70 percent dark energy, 25 percent dark matter, and about 5 percent of the normal “baryonic” matter that we can see.

Euclid’s Mission

ESA’s Euclid mission has the ambitious goal of better understanding dark energy and dark matter. It is a massive scientific effort, involving a consortium of about 1,000 people based primarily in Europe, but also around the world. Delayed due to COVID-19, Euclid is now set to launch sometime between July and December 2022.

Euclid will use his telescope to look at the last 10 billion years of the universe’s history, when dark energy is believed to have driven the expansion of the universe. Light from distant, ancient galaxies takes many billions of years to reach our solar system, which means astronomers see these galaxies as they were billions of years ago.

Coles is the only Ireland-based researcher at Euclid. He is interested in why galaxies tend to cluster in clusters rather than randomly spread out in space and how some kind of cosmic glue – called dark energy – holds the clusters together. He admits that no one knows what this glue is, or how to find it. “If you ask, what is dark energy, the true scientific answer is that no one knows,” he says.

Euclid, in its most basic form, is a space telescope satellite with a diameter of 1.2 m. It is not particularly large because the largest telescope in space, the Hubble Space Telescope, has a width of 2.4 meters. Yet Euclid has an impressive camera attached to its telescope, which can take high resolution images over a large area of ​​the sky.

These images will enable scientists to look back in time, deep into the early universe, to trace the evolution and formation of galaxies, galaxy clusters and more. Euclid may discover a lot, says Coles, but the big-ticket object that’s driving the mission is hunting for dark energy, and whether that energy, once found, tends to be constant or varying. is determined.

If dark energy is found to be stable, it would fit with existing ideas of the universe, as described by Einstein. This result will disappoint all astrophysicists who expect that dark energy, once discovered and measured, will represent something new, exciting and outside the existing physical laws.

The dark forces of the universe remain hidden, but physicists infer their presence from how visible matter behaves. Invisible gravitational effects are thought, for example, to hold together superclusters of the Solar System, galaxies, galaxy clusters, even galaxies that would otherwise fall apart.

The invisible forces of gravity are believed to bend light around visible matter, in a process called “weak lensing”. This results in distortion, stretching, or magnification in the shape of galaxies, and the resulting pattern can be used to calculate the distribution of dark matter.

Measuring ‘Redshift’

Measuring “redshift” may provide further clues. The term dates back to 1929 when Edwin Hubble discovered that the universe is expanding, and galaxies – mostly – are moving away from us. Hubble found that the wavelengths of light emitted from galaxies shift from shorter wavelengths to longer wavelengths as the galaxies move away from us. The light, Hubble said, was “re-shifted” from the shorter UV wavelengths to the longer red wavelengths.

Today, computing the redshift of galaxies helps scientists produce 3D maps of the universe. Scientists use redshift to measure each galaxy’s distance from us, the rate of the universe’s accelerated expansion, and the speed of the galaxies in relation to each other. As a result, the nature of dark energy, which is thought to drive it, can be inferred.

Scientists get excited when they think about what dark energy might actually be. There are some who believe that dark energy represents an entirely new physics outside of known physical laws, but until such theories can be tested with Euclid’s data, it is unlikely to be something that exists. Nothing more than a given name will remain which scientists do not understand. Any new theory of how the universe works would have to fit with Euclid’s observational data.

If Euclid discovers, measures and measures dark energy and dark matter, it would be one of the greatest scientific achievements in history. It would open the door to something Einstein tried but failed to achieve: a theory of everything that would move from the physics of “big stuff” like stars, planets and galaxies to the strange quantum physics of tiny atoms and subatomic particles. connects with.