Searching for the dark universe: the Euclid telescope has discovered an impressive Einstein ring very close to Earth

Although this galaxy has long been known to astronomers, no one has ever observed the ring so close to Earth before.

From the first images to the surprising result

• Verification phase: After launch, Euclid needed time for calibration and tests. In September 2023, it sent a series of "blurry" images back to Earth, but one of the images caught the attention of Bruno Altieri, a scientist working with the Euclid archives.
• Theunexpected finding: A detailed analysis confirmed that a perfect Einstein ring had formed in the core region of galaxy NGC 6505 - a gravitational lensing effect where a massive object (the galaxy in the foreground) distorts and amplifies the light from a distant, as yet unnamed galaxy 4.42 billion light years away.

Why Einstein's rings are so important

Albert Einstein predicted in his general theory of relativity that massive bodies bend space-time and focus light like a lens. If the arrangement of the "lens object" and the "light source" turns out to be nearly perfect, we see a bright ring around the observer galaxy.

• Rare and valuable: Such "strong lenses" are extremely rare. Scientists can use them to measure the expansion rate of the Universe, search for traces of dark matter and dark energy, and study light "squeezed" by a background object in more detail.
• Previous estimates: Until now, fewer than a thousand objects with strong gravitational lensing effects have been known. "Euclid, however, can detect up to 100,000 such structures, promising a real breakthrough in understanding the cosmic scale.

Key features of Euclid

Euclid's main mission is to explore the so-called dark universe by collecting data on the distribution of billions of galaxies up to 10 billion light years away. The resulting 3D catalogue will allow scientists to:

1. Measure the effects of weak gravitational lensing ("weak lensing"), where the shapes and sizes of background galaxies are weakly distorted by dark matter fields.
2. Clarify the dynamics of expansion: understand how the Universe is accelerated by dark energy.
3. Determine the contribution of dark matter: analyse where and how it affects light from distant objects.

"Euclid is on its way to take off

The telescope began basic mapping of the sky on 14 February 2024. Its goal is to create the most detailed 3D map of the Universe in the history of astronomy. To find such an impressive gravitational lens so early in the mission is a sign of the many discoveries to come.

• Significance of the result: According to the scientists, the fact that a perfect Einstein ring was found in the "known" galaxy NGC 6505 clearly demonstrates the high resolution of the Euclidean instruments.
• Near-term prospects: in addition to strong lensing, Euclid is designed to detect millions of instances of weak gravitational lensing that are invisible to the naked eye, which is especially important for compiling a complete picture of cosmic evolution.

Source: "Euclid: A complete Einstein ring in NGC 6505", Astronomy and Astrophysics (2025). DOI: 10.1051/0004-6361/202453014