The Dark Universe Is Waiting. What Will the Euclid Telescope Reveal?
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The European Space Agency mission, which launched on Saturday, will capture billions of galaxies to create a cosmic map spanning space and time.
By Katrina Miller
Published July 1, 2023
Updated July 2, 2023
At 11:12 a.m. on Saturday, the Euclid spacecraft launched into space on its mission to chart the history of our universe as far back as 10 billion years ago.
The space telescope, built by the European Space Agency, will use its instruments to record more than a third of the extragalactic sky over the next six years, creating the most accurate three-dimensional map of the cosmos to date.
Researchers plan to use Euclid’s map to explore how dark matter and dark energy — mysterious stuff that makes up 95 percent of our universe — have influenced what we see when we look out across space and time.
“Euclid is coming at a really interesting time in the history of cosmology,” said Jason Rhodes, a physicist at NASA’s Jet Propulsion Laboratory who leads Euclid’s U.S. science team. “We are entering a time when Euclid is going to be great at answering questions that are just now emerging. And I am certain that Euclid is going to be fantastic for answering questions we haven’t even thought of.”
The spacecraft lifted off from Cape Canaveral, Fla., on a SpaceX Falcon 9 rocket. The weather was almost perfect for the flight. Euclid, still attached to the rocket’s second stage, separated from its booster three minutes after launch, amid a round of applause. It entered a stable orbit around Earth nearly nine minutes after the flight. About 40 minutes later, the telescope separated from the second stage and began a journey of a million miles to a point in space where the mission’s scientific journey would begin.
“Unbelievable,” said Guadalupe Cañas Herrera, a theoretical cosmologist on the Euclid mission, when asked about the launch on the ESA video stream. “I’m super emotional, but also extremely thankful for everything that has been done so far so that we can actually have a telescope in space.”
The European astrophysics mission had no choice but to fly American. ESA had planned to launch the spacecraft on either a Russian Soyuz rocket or Europe’s new Ariane 6 rocket. But because of a break in the European-Russian space relationship after the invasion of Ukraine, and delays for Ariane 6, ESA moved some launches to SpaceX, including Euclid.
The spacecraft will not be alone in peering into the cold storage of our universe. But unlike the Hubble and James Webb Space Telescopes, which focus deeply on one part of the sky at a time, scientists will use Euclid to cover wide swaths of the extragalactic sky at once. In three of the regions it records, Euclid will reach back even farther, imaging the structure of the universe about one billion years after the Big Bang.
One of the space telescope’s targets is dark matter, the invisible glue of the cosmos that doesn’t emit, absorb or reflect light. Dark matter has so far evaded direct detection, despite physicists’ best efforts, but they know it exists because of its gravitational influence on the way that galaxies move.
Dark energy, on the other hand, is a much more mysterious force that pushes galaxies apart — so much so that our universe is expanding at an accelerating rate.
Euclid’s maps of the cosmos will reveal how dark matter is distributed across space-time based on how it warps the light from galaxies behind it, an effect known as weak gravitational lensing. (That’s distinct from strong gravitational lensing, more dramatic warping by galactic clusters that creates arcs, rings, or even multiple images of a single source.)
These measurements contribute to more direct efforts to figure out what dark matter actually is.
“We’re looking for the same thing from different angles,” said Clara Nellist, a particle physicist at CERN in Europe who is not a part of the Euclid mission. Researchers on Earth-based experiments hunt for signs of dark matter particles colliding with their detectors. “Any information we gather about how it’s distributed in our universe helps us to look for it in our collisions in a more focused way,” Dr. Nellist said.
With Euclid, scientists hope to be able to test if Albert Einstein’s theory of general relativity works differently on cosmological scales. That could be related to the nature of dark energy: whether it is a constant force in the universe, or a dynamic one whose properties vary with time.
“If we find out this is not a constant, but something that changes in time, then it would be revolutionary,” said Xavier Dupac, an ESA cosmologist on the Euclid mission, because it would overturn what is known about fundamental physics. Such a discovery could even shed light on the ultimate fate of what seems to be our ever-expanding universe.
Euclid hosts a visible imager consisting of a 600-megapixel camera that can photograph an area as wide as two full moons’ worth of sky at a time. With this instrument, scientists will be able to glean how the shapes of galaxies get distorted by dark matter in front of them.
It also has a near-infrared spectrometer and photometer, which will be used to both record galaxies in nonvisible wavelengths as well as measure their redshift, the wavelength-stretching effect in light arriving from the faraway cosmos that results from the expansion of the universe. When used in conjunction with a suite of ground-based instruments — including the Subaru and Canada-France-Hawaii Telescopes at Mauna Kea Observatory, and eventually the Vera C. Rubin Observatory in Chile — scientists will be able to convert redshift into measurements of distance from Earth.
While Euclid launched successfully, it is now setting off on a journey nearly a million miles from Earth to orbit around what is known as the second Lagrange point, or L2 — a place in the solar system where the Earth and sun’s gravitational pulls are in balance with the motion of the satellite. Facing directly away from the sun, this location also strategically places Euclid in a spot to conduct wide surveys of the sky without the Earth or the moon blocking its view. The James Webb Space Telescope orbits L2 for the same reason.
It will take about a month for the spacecraft to arrive at L2, and another three months to test the performance of Euclid’s instruments before it begins sending data back to Earth for scientists to analyze. That data will be publicly released in 2025, 2027 and 2030.
At a prelaunch news briefing last week, Yannick Mellier, an astronomer at the Institut d’Astrophysique de Paris, said that beyond its main science goals, Euclid will create a unique sky survey of 12 billion galaxies with an image quality rivaling that of the Hubble.
It will be “a gold mine for all fields of astronomy for several decades,” Dr. Mellier said.
A version of this article appears in print on July 4, 2023, Section D, Page 3 of the New York edition with the headline: Hubble and Webb, You’ve Got Company
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