Launch of the European “Dark Energy Telescope” to explore the biggest mysteries of cosmology

SpaceX launched the European Space Agency’s $1.5 billion Euclid Space Telescope on Saturday, an ambitious and unique attempt to determine the nature of dark matter — an unknown substance pervading the universe — and dark energy, the mysterious repulsive force accelerating the expansion of the universe.

“It is very difficult to find a black cat in a dark room, especially if there is no cat there,” said Henk Hoekstra, an astronomer at Leiden University and coordinator of Euclid Science. “This is a situation we find ourselves in a little bit because we have these observations but lack a good theory.

“So far, no one has come up with a good explanation for dark matter, dark energy, and other challenges also related to particle physics. … Euclid’s launch really (carries) cosmology into the future. It’s the first space mission designed to study dark energy.”

In 1998, astronomers mapping the expansion of the universe expected to see a slowdown due to the gravitational pull of all its components. They were amazed to discover that the expansion of space and everything in it began to accelerate 5-6 billion years ago. The unknown force driving this acceleration was called dark energy.

Researchers have since concluded that dark energy accounts for nearly three-quarters of the collective energy budget of the entire universe. Dark matter makes up about 24% of the universe, while atoms and molecules make up normal matter – Earth, humans, stars and galaxies – only 5%.

By studying subtle changes in light from galaxies over the past 10 billion years, Euclid’s cameras will help scientists discover whether dark energy is consistent with an unchanging “cosmological constant” predicted by Einstein’s general theory of relativity or whether current understanding of gravity needs to be addressed. review.

Yannick Miller, an astronomer at the Astrophysic Institute in Paris and a member of Euclid’s science team, put it this way:

The goal of Euclid’s mission is to provide answers to the following questions: Why is the expansion of the universe accelerating, which translates to What is the nature of dark energy? Is it a cosmological constant? Is it dynamic dark energy whose properties may vary with time? Or is it a deviation from general relativity on scales cosmic?

At the same time, Euclid will also study the nature of dark matter, a sea of ​​particles that do not emit or reflect light or other electromagnetic radiation, but clearly show the effects of gravity. Dark matter keeps galaxies from escaping and influences how galaxies have evolved and come together over the 13.7 billion years since the Big Bang.

“Euclid will investigate the distribution of dark matter and the distribution of galaxies at unprecedented resolution from space,” said Millier. “It will also reconstruct the cosmic history of the universe over the past 10 billion years.”

It will do this by imaging more than 10 billion galaxies. Software on Earth will help identify the 1.5 billion or more best candidates and analyze how their shapes are distorted by the invisible dark matter clouds that fill the space between Euclid and its targets.

The technique, known as weak gravitational lensing, is similar in concept to the way water slightly distorts the shapes of rocks strewn across a stream. It is a very subtle effect in cosmological terms, requiring complex software, powerful computers and more than 1,500 scientists at nine research centers to detect it.

But if all goes well, Euclid “will directly observe the distribution of dark matter using a gravitational lensing effect that modifies the shapes of galaxies, which are deflected by the distribution of dark matter along a given line of sight,” Millier said. “This will provide the distribution of dark matter that is not visible in a Euclidian field.”

Spectral observations of tens of millions of galaxies will allow researchers to determine distances and velocities in three dimensions, shedding light on whether dark energy is, in fact, the force behind the acceleration of cosmic expansion or whether another explanation is needed.

The mission began at 11:12 a.m. EST Saturday when a SpaceX Falcon 9 rocket blasted to life at Cape Canaveral Space Force Station. After a quick round of computer checks, the rocket was launched to leapfrog 1.7 million pounds of thrust, putting on a spectacular weekend sky show for area residents and tourists.

41 minutes later, after two salvoes of the rocket’s second-stage engine, Euclid was launched to fly solo. The Falcon 9 first stage, as usual at SpaceX, flew itself to land on an offshore drone.

The European Space Agency, or ESA, was preparing to launch the Euclid Space Telescope last year on a Russian Soyuz rocket that took off from Kourou, French Guiana. But in the aftermath of the Russian invasion of Ukraine, those plans collapsed, leaving Euclid without a flight into space.

Last July, the European Space Agency approached SpaceX about a possible launch of the company’s Falcon 9 rocket. By the end of the year, the contracts were in effect and the team was able to move forward with the Saturday launch.

“We owe … a huge thank you to SpaceX,” said Mike Healy, head of science projects at the European Space Agency. “Without them, our satellite will remain on Earth for two years.”

Euclid is headed for a region of space nearly a million miles from Earth – Lagrange Point 2 – where the gravity of the Sun and Earth combine to form a calm zone where the spacecraft can stay in place with minimal maneuvering and fuel usage. The James Webb Space Telescope is also operating at L2.

The 4,760-pound Euclid is equipped with a near-perfect 3-foot-by-11-inch primary mirror and two instruments: a 600-megapixel visible-light camera and a 64-megapixel infrared spectrophotometer. The telescope’s field of view is roughly twice the size of the full moon.

After a month-long checking and calibration period, Euclid will begin mapping the 15,000 square degrees of the sky, which includes all of the space outside the Milky Way, imaging galaxies and galaxy clusters dating back 10 billion years.

It will capture the transition from the initial slowing down of the gravitationally driven universe to an era of accelerated expansion under the emerging dominance of dark energy.

“Euclid can, in one go, present a much larger field than what can be achieved by Hubble,” said Rene Leurige, Euclid Project Scientist at the European Space Agency. “During its entire lifetime, Hubble never covered more than 100 square degrees, and Euclid could do that in 10 days. So in order to get 15,000 square degrees, which is the size of our sky survey, we need these big sky images.”

It would take Euclid six years to complete his map of the sky, generating approximately 100 gigabytes of compressed data per day, or an estimated 70,000 terabytes over the course of the mission.

“Your iPhone probably has 10 megapixels,” said Jason Rhodes, member of the Euclid Research Consortium. So the two Euclid cameras together have about 700 megapixels. We’ll be taking pictures with these cameras every few minutes for six years.

“But the amount of data we’re sending is down compared to the amount of data that’s entirely in the archive at the end of the process, and that’s another factor of a thousand.”

These images will include 8 billion galaxies, Gaitee Hussain, chief of science at ESA, said, “The best between one and a half and two billion galaxies will be selected for the weak lensing experiment.”

“We will collect millions and tens of millions of spectral redshifts, in addition to billions of optical redshifts, in order to understand the distances of the galaxies we are looking at,” she added.

“That means huge data rates, not only for data delivery back to Earth, but also in terms of data communication… This is what is needed to answer what is arguably the fundamental question in physics and cosmology today, which is, What is the universe actually made of?”