Euclid Telescope Maps the Dark Universe

The universe is a massive puzzle, yet we are missing most of the pieces. Everything we can see, touch, or interact with—stars, planets, gas, and dust—makes up only about 5% of the cosmos. The remaining 95% is composed of mysterious entities known as dark matter and dark energy. To solve this mystery, the European Space Agency (ESA) has deployed Euclid, a sophisticated space telescope designed to create the largest, most accurate 3D map of the universe ever produced.

The Mission to Illuminate the Dark Sector

Euclid is not just another telescope; it is a time machine and a surveyor combined. Launched on July 1, 2023, aboard a SpaceX Falcon 9 rocket from Cape Canaveral, Florida, its destination was the Sun-Earth Lagrange Point 2 (L2). This is a stable gravitational point located 1.5 million kilometers (about 1 million miles) from Earth, which it shares with the James Webb Space Telescope (JWST) and the Gaia mission.

While telescopes like James Webb focus on drilling deep into tiny patches of the sky to see the earliest galaxies, Euclid takes a different approach. It is a wide-angle surveyor. Over its primary six-year mission, Euclid will observe more than one-third of the entire sky. Its goal is to catalogue the shapes, distances, and motions of billions of galaxies, looking back over 10 billion years of cosmic history.

By analyzing this massive dataset, scientists aim to understand the two “dark” components that rule our universe:

  • Dark Matter: This invisible substance acts like cosmic glue. It exerts gravity, holding galaxies together. Without it, stars within galaxies would fly apart because visible matter does not provide enough gravity to hold them.
  • Dark Energy: This is even more mysterious. It acts as a repulsive force that pushes the universe apart, causing the expansion of the cosmos to accelerate.

How Euclid Sees the Invisible

Since dark matter and dark energy cannot be seen directly, Euclid detects them by observing their effects on visible matter. It uses two primary scientific instruments to gather this data:

1. The VIS (Visible Instrument)

The VIS is a massive camera capable of taking incredibly sharp images of galaxies across a wide field of view. It operates in the same visible wavelengths that the human eye can see. The sharpness is vital because Euclid is looking for “weak gravitational lensing.”

Gravitational lensing happens when the gravity of massive objects (like dark matter concentrations) bends the light coming from background galaxies. This bending causes tiny distortions in the shapes of those background galaxies. By measuring the shapes of millions of galaxies with extreme precision, the VIS instrument allows scientists to map where dark matter is distributed across the universe.

2. The NISP (Near-Infrared Spectrometer and Photometer)

The NISP operates in infrared light. Its primary job is to measure the “redshift” of galaxies. As the universe expands, light from distant objects gets stretched, shifting it toward the red end of the spectrum.

By measuring this redshift, NISP determines exactly how far away each galaxy is. When you combine the precise 2D images from VIS with the distance data from NISP, you get a 3D map. This map shows how the distribution of galaxies has changed over 10 billion years, revealing how dark energy has stretched the universe over time.

Early Success and First Images

Following its arrival at L2 and a period of calibration, Euclid released its first full-color images in November 2023. These images proved the telescope is performing beyond expectations.

  • The Perseus Cluster: Euclid captured a shot of the Perseus Cluster of galaxies. In a single image, it resolved 1,000 galaxies belonging to the cluster and more than 100,000 additional galaxies further in the background. Many of these faint galaxies had never been seen before.
  • IC 342 (The Hidden Galaxy): This spiral galaxy is usually difficult to see because it sits behind the dust of our own Milky Way. Euclid’s infrared capabilities allowed it to peer through the dust and map the stars within this galaxy, providing crucial data on how stars form and evolve.
  • The Horsehead Nebula: While this is a famous target for many telescopes, Euclid provided a panoramic view that was both wide and incredibly sharp, revealing new details about the nursery of stars within the nebula.

A Global Collaboration

The Euclid mission represents a massive coordinate effort. The Euclid Consortium comprises more than 2,000 scientists from 300 institutes across 13 European countries, along with researchers from the United States, Canada, and Japan.

While the European Space Agency leads the mission, NASA played a critical role. NASA provided the detectors for the NISP instrument. Industrial partners were also key: Thales Alenia Space (Italy) built the satellite service module, and Airbus Defence and Space (France) developed the payload module, including the telescope and optical bench.

Why This Map Matters

The data Euclid collects will help physicists test the general theory of relativity on cosmic scales. Albert Einstein’s theory works perfectly in our solar system, but some scientists wonder if gravity behaves differently across billions of light years.

If Euclid finds that gravity acts differently than Einstein predicted, it could revolutionize physics. Alternatively, if the data fits the current models, it will help pin down the exact properties of dark energy. For example, is dark energy a constant force (the “cosmological constant”), or does it change strength over time? Euclid is the best tool humanity has built to answer this question.

Frequently Asked Questions

How is Euclid different from the James Webb Space Telescope? Think of James Webb as a microscope and Euclid as a wide-angle camera. James Webb looks at very small patches of the sky in extreme detail to study individual objects. Euclid looks at huge sections of the sky to study the structure of the universe as a whole. Euclid can image an area of the sky 100 times larger than James Webb can in a single pointing.

How long will the mission last? The nominal mission lifetime is six years. However, space telescopes often outlive their planned timelines if their hardware remains healthy and they have enough fuel to maintain their orbit.

Can Euclid see inside our own galaxy? Yes. While its main goal is to look deep into the cosmos, Euclid will also observe objects within the Milky Way and our local group of galaxies. It is expected to discover tens of thousands of new brown dwarfs (failed stars) and stray planets in our galaxy.

What is the “cosmic web”? The cosmic web is the structure of the universe. Galaxies are not scattered randomly; they are arranged in giant filaments and sheets, separated by massive voids. Dark matter provides the scaffolding for this web. Euclid’s 3D map will reveal this structure more clearly than ever before.