The Euclid mission — led by ESA (European Space Agency) with contributions from NASA — aims to find out why our universe is expanding at an accelerating rate. Astronomers use the term “dark energy” to refer to the unknown cause of this phenomenon, and Euclid will take images of billions of galaxies to learn more about it. A portion of the mission’s data was released to the public by ESA released on Wednesday, March 19.
This new data has been analyzed by mission scientists and provides a glimpse of Euclid’s progress. Deemed a “quick” data release, this batch focuses on select areas of the sky to demonstrate what can be expected in the larger data releases to come and to allow scientists to sharpen their data analysis tools in preparation.
The entirety of the Euclid mission’s Deep Field South region is shown here. It is about 28.1 square degrees on the sky. Euclid will observe this and two other deep field regions for a total of about 40 weeks during its 6-year primary mission. Credit: ESA/Euclid/Euclid Consortium/NASA; image processing by J.-C. Cuillandre, E. Bertin, G. An-selmi" data-animated="false">
The entirety of the Euclid mission’s Deep Field South region
The entirety of the Euclid mission’s Deep Field South region is shown here. It is about 28.1 square degrees on the sky. Euclid will observe this and two other deep field regions for a total of about 40 weeks during its 6-year primary mission.
Credit: ESA/Euclid/Euclid Consortium/NASA; image processing by J.-C. Cuillandre, E. Bertin, G. An-selmi
The data release contains observations of Euclid’s three “deep fields,” or areas of the sky where the space telescope will eventually make its farthest observations of the universe. Featuring one week’s worth of viewing, the Euclid images contain 26 million galaxies, the most distant being over 10.5 billion light-years away. Launched in July 2023, the space telescope is expected to observe more than 1.5 billion galaxies during its six-year prime mission.
By the end of that prime mission, Euclid will have observed the deep fields for a total of about 40 weeks in order to gradually collect more light, revealing fainter and more distant galaxies. This approach is akin to keeping a camera shutter open to photograph a subject in low light.
The first deep field observations, taken by NASA’s Hubble Space Telescope in 1995, famously revealed the existence of many more galaxies in the universe than expected. Euclid’s ultimate goal is not to discover new galaxies but to use observations of them to investigate how dark energy’s influence has changed over the course of the universe’s history.
In particular, scientists want to know how much the rate of expansion has increased or slowed down over time. Whatever the answer, that information would provide new clues about the fundamental nature of this phenomenon. NASA’s Nancy Grace Roman Space Telescope, set to launch by 2027, will also observe large sections of the sky in order to study dark energy, complementing Euclid’s observations.
The entirety of the Euclid mission’s Deep Field South region is shown here. It is about 28.1 square degrees on the sky. Euclid will observe this and two other deep field regions for a total of about 40 weeks during its 6-year primary mission. Credit: ESA/Euclid/Euclid Consortium/NASA; image processing by J.-C. Cuillandre, E. Bertin, G. An-selmi" data-animated="false">
The entirety of the Euclid mission’s Deep Field South region
The entirety of the Euclid mission’s Deep Field South region is shown here. It is about 28.1 square degrees on the sky. Euclid will observe this and two other deep field regions for a total of about 40 weeks during its 6-year primary mission.
Credit: ESA/Euclid/Euclid Consortium/NASA; image processing by J.-C. Cuillandre, E. Bertin, G. An-selmi
Looking Back in Time
To study dark energy’s effect throughout cosmic history, astronomers will use Euclid to create detailed, 3D maps of all the stuff in the universe. With those maps, they want to measure how quickly dark energy is causing galaxies and big clumps of matter to move away from one another. They also want to measure that rate of expansion at different points in the past. This is possible because light from distant objects takes time to travel across space. When astronomers look at distant galaxies, they see what those objects looked like in the past.
For example, an object 100 light-years away looks the way it did 100 years ago. It’s like receiving a letter that took 100 years to be delivered and thus contains information from when it was written. By creating a map of objects at a range of distances, scientists can see how the universe has changed over time, including how dark energy’s influence may have varied.
But stars, galaxies, and all the “normal” matter that emits and reflects light is only about one-fifth of all the matter in the universe. The rest is called “dark matter” — a material that neither emits nor reflects light. To measure dark energy’s influence on the universe, astronomers need to include dark matter in their maps.
