Europe's Euclid telescope launches to figure out dark energy, the universe, and everything

We speak to project scientist on effort to build 3D map of space going back ten billion years

Interview Euclid, an advanced telescope built by the European Space Agency to study the nature of dark energy and dark matter, blasted off into space aboard a SpaceX Falcon 9 rocket on Saturday.

The rocket launched from Cape Canaveral in Florida at 1112 ET (1512 UTC) carrying the 4.5-metre-tall (15 foot) instrument packed tightly in its nose cone. The goal is to give Euclid a boost into the second Lagrange point (L2), a region 1.5 million kilometres (1 million miles) away from Earth where the Sun's gravitational pull will ensure a stable position. 

You can replay the launch and livestream here.

After it arrives at its target destination about four weeks post-launch, the billion-euro satellite will begin aligning its telescope and activate its instruments: a visible light camera, and a near-infrared spectrometer and photometer. Its mass in orbit will be two tonnes, we're told.

Euclid will use its tools to scan the universe, snapping images of galaxies - the oldest ones dating back to those formed ten billion years ago. By probing these cosmic structures, scientists can measure their position and distance to construct a 3D map of galaxies. They can use this to study how the universe expanded and evolved over time.

The birth of the universe has been traced back to the Big Bang some 13.8 billion years ago. The energy leftover from the violent explosion formed the first atoms, which then formed the first stars, planets, and galaxies, beginning about 400,000 years later. Scientists believe that the universe is ballooning in size as new stars, planets, and galaxies fill the void, and that the rate of expansion appears to be accelerating.

But they disagree on how fast it's growing, mainly because the available data doesn't add up.

"Ever since astronomers discovered the expansion of the universe in the 1920s, there have been continuous efforts to improve the accuracy," Mike Seiffert, a project scientist working at NASA's Jet Propulsion Laboratory who contributed to the Euclid mission, told The Register.

"These are challenging measurements. Sometimes the results of different types of measurements disagree.

"There is a tension between the expansion rate as determined by cosmic microwave background measurements, which are sensitive to the conditions in the early universe, 370,000 years after the Big Bang, and supernova measurements, which are sensitive to the conditions in the last few billion years."

Rendering of Europe's Euclid telescope

Rendering of Europe's Euclid telescope ... Source: ESA. Click to enlarge

Objects appear to be moving away from each other at a pace that increases the further they are from each other. To try and explain why, cosmologists have chalked it up to dark energy, a mysterious phenomenon that acts in an opposite way to gravity. Over relatively short distances, matter likes to clump together. Giant clouds of gas and dust collapse to create stars and planets; objects such as black holes can collide with one another; and galaxies inching closer to one another eventually merge. Gravity pulls things closer together - even dark matter, the invisible substance that is believed to make up 25 percent of the universe. 

Over much longer distances, however, dark energy is more dominant and pushes things apart.

We know so little about it because its effect on Earth ... is extremely small

"We don't know what dark energy is," Sieffert said. "We know so little about it because its effect on Earth, or the Solar System, or of our own galaxy is extremely small. It is only by looking at the largest scales in the universe that we can detect it at all, and that did not happen until the late 1990s. We are now trying to take the next steps by using powerful telescopes to measure an enormous number of galaxies covering very large distances. Euclid will be the first space mission dedicated to such studies."

By building a three-dimensional map of objects, spanning across a third of the sky stretching back to ten billion years, cosmologists can study a sliver of the universe and figure out how its structure evolved over time.

Not only will this shed light on how fast it may be expanding, but it could also help scientists better understand dark energy and dark matter. Dark energy pushes the universe apart, and dark matter helps it come together, or so it's theorized.

"We will also measure the galaxy shapes of over a billion galaxies. There is an effect called 'weak gravitational lensing' in which the intervening matter between distant galaxies and us subtly alters the shapes of the distant galaxies," Sieffert explained.

"By studying this effect, we can learn about the distribution of matter between us and distant galaxies. That distribution is affected by the attractive force of gravity and the repulsive nature of dark energy. With a detailed statistical study, we can make progress on the nature of dark energy."

Up to about 70 percent of the universe is estimated to be dark energy. The discrepancy between the rates of its expansion hint that there is something more to the problem than simply measurement errors. Instead, there is something more fundamental that cosmologists haven't yet figured out.

"It is unknown whether this tension is due to our incomplete understanding of the physics that governs the expansion, or whether instead there is incomplete understanding of our cosmic microwave background measurements or the physics of supernovae," Sieffert said.

"We don't even know if [dark energy] is a separate, new, component of the universe, or a subtle modification of Einstein's theory that leads to the appearance of a repulsive force at very large distances."

Euclid is the next best instrument built to study humanity's biggest mysteries: how did the universe begin? Where is it going? Will it end?

"In Western civilization we have been fascinated with the universe for thousands of years. The ancient Greeks asked questions about what the universe is made of and whether it is finite or infinite and how it behaves. Other civilizations have asked similar questions," Sieffert said.

"It is simply amazing to me personally that we can actually make measurements of the properties of the universe on the largest observable scales. It inspired me when I was younger, and I hope thinking about the universe and studying it will inspire the next generation of young people as well." ®

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