Euclid Telescope Maps Dark Matter

The European Space Agency (ESA) has officially begun one of the most ambitious astronomical surveys in history with the Euclid space telescope. While telescopes like Hubble and James Webb focus on individual objects with high magnification, Euclid is doing something different. It is creating the largest and most accurate 3D map of the universe ever produced. This mission is our best hope for understanding the invisible forces that make up 95% of our cosmos: dark matter and dark energy.

The Mission to Map the Invisible

Launched on July 1, 2023, aboard a SpaceX Falcon 9 rocket from Cape Canaveral, Florida, Euclid traveled 1.5 million kilometers to reach its operational home at Lagrange Point 2 (L2). This is the same orbital neighborhood occupied by the James Webb Space Telescope. However, Euclid has a fundamentally different job.

The primary goal of the six-year mission is to observe billions of galaxies across more than one-third of the sky. By looking back over 10 billion years of cosmic history, Euclid will chart the distribution of matter over time and space.

Scientists know that “normal” matter—stars, planets, gas, and us—makes up only about 5% of the universe. The rest is comprised of two mysterious components:

• Dark Matter (approx. 25%): Invisible material that acts as “cosmic glue,” exerting gravitational pull to hold galaxies together.
• Dark Energy (approx. 70%): A repulsive force that is accelerating the expansion of the universe, pushing galaxies apart.

Euclid acts as a surveyor. It maps the geometry of the universe to reveal how these two forces compete against each other.

How Euclid Sees the Dark Universe

Since dark matter is invisible and does not reflect or emit light, Euclid cannot photograph it directly. Instead, it detects dark matter through its gravitational influence on visible matter.

This relies on a phenomenon called gravitational lensing. When light from a distant galaxy travels toward Earth, it passes through massive clouds of dark matter. The gravity of this dark matter bends the light, slightly distorting the shape of the background galaxy.

Euclid is designed to measure these tiny distortions with extreme precision.

The Instruments

To achieve this, the telescope carries two cutting-edge instruments supplied by the Euclid Consortium, a group of 2,000 scientists from 300 institutes across Europe, the US, Canada, and Japan.

1. VIS (Visible Instrument): This high-quality camera captures visible light. It measures the shapes of galaxies with sharpness comparable to the Hubble Space Telescope but covers a field of view that is significantly larger.
2. NISP (Near-Infrared Spectrometer and Photometer): This instrument, which includes detectors provided by NASA, analyzes infrared light. It measures the redshift of galaxies, which tells scientists how fast they are moving away from us. This data is essential for calculating the distance to each galaxy, providing the third dimension (depth) to the map.

Early Results: The First Images

In November 2023 and May 2024, ESA released the first full-color images from Euclid, proving the telescope’s capabilities exceeded expectations. These “Early Release Observations” demonstrated Euclid’s ability to capture vast areas of the sky in a single shot while maintaining sharp focus on both foreground and background objects.

The Perseus Cluster

One of the headline images featured the Perseus Cluster of galaxies. In a single pointing, Euclid captured 1,000 galaxies belonging to the cluster and more than 100,000 additional galaxies further in the background. Many of these faint background galaxies had never been seen before. This image provided the first concrete evidence that Euclid can map the faint distortions caused by dark matter across massive cosmic structures.

The Hidden Galaxy (IC 342)

Euclid also peered through the dust of our own Milky Way to image IC 342, often called the “Hidden Galaxy.” While infrared telescopes usually struggle to see through dust without losing field of view, Euclid managed to resolve individual stars within this galaxy while capturing its entire spiral structure. This validates the telescope’s ability to study galaxy formation and evolution alongside its dark matter studies.

The Horsehead Nebula

Euclid provided a stunning, panoramic view of the Horsehead Nebula. While this object is a favorite target for telescopes, Euclid captured the surrounding molecular clouds in high resolution within a single hour of observation. This speed suggests the mission will be able to complete its massive sky survey within the planned six-year timeframe.

Why This Map Matters

The data collected by Euclid will help physicists answer fundamental questions about the laws of physics. Currently, our understanding of gravity is based on Albert Einstein’s Theory of General Relativity. However, the behavior of dark energy suggests there are gaps in this theory on a cosmic scale.

By measuring how the expansion rate of the universe has changed over the last 10 billion years, Euclid will help determine if dark energy is a constant force (a “cosmological constant”) or if it changes over time. If Euclid finds that dark energy is dynamic, it would require a major rewrite of standard physics models.

Furthermore, the map acts as a timeline. By observing the “cosmic web”—the filament-like structures where galaxies cluster—at different eras, scientists can see exactly how dark matter guided the growth of the universe from the Big Bang to today.

Frequently Asked Questions

How is Euclid different from the James Webb Space Telescope? The main difference is the field of view. James Webb is like a microscope; it looks at very small patches of the sky in incredible detail to see the first stars. Euclid is like a wide-angle camera; it sacrifices some depth to capture massive sections of the sky quickly to map the overall structure of the universe.

Will Euclid see dark matter directly? No. Dark matter does not interact with light. Euclid detects it indirectly by measuring how its gravity bends light from galaxies behind it.

How much of the sky will Euclid map? Euclid will map approximately 36% of the celestial sphere. It focuses on the areas of the sky outside of our own Milky Way galaxy, as the dust and stars of our own galaxy would block the view of the deep universe.

How long will the mission last? The primary mission is scheduled to last six years. However, if the hardware remains healthy and fuel allows, the mission could be extended to gather even more precise data.

Who runs the Euclid mission? Euclid is an ESA (European Space Agency) mission. However, it has significant contributions from NASA, which provided the detectors for the NISP instrument, and the Euclid Consortium, which handles the data processing and scientific analysis.