Albert Einstein predicted more than a hundred years ago that massive objects like galaxies and galaxy clusters could bend the light coming from distant sources. This bending effect creates a magnifying lens in space, making distant objects appear distorted or even forming circular patterns called Einstein rings. Recently, scientists discovered a new Einstein ring, now called Altieri’s Ring, which has excited the astronomy world.

What is an Einstein ring?

When light from a distant galaxy travels through space and passes near a very large object, like another galaxy, the gravity of that object bends the light. This bending effect is called gravitational lensing. It can make the light appear in different spots, creating unusual shapes. If everything lines up just right—the observer (like a telescope), the bending galaxy, and the distant galaxy—the light forms a bright, circular shape. Scientists call this an Einstein ring.

This phenomenon was first predicted by Albert Einstein in his General Theory of Relativity. He suggested that space and time are like a flexible fabric, and massive objects bend this fabric, changing the path of light. American physicist John Wheeler described this theory with the words, “Matter tells spacetime how to curve, and curved spacetime tells matter how to move.”

The first Einstein ring was discovered in 1998, more than 80 years after Einstein predicted it. Since then, astronomers have found several more, but they are still rare.

Discovery of Altieri’s ring

The European Space Agency’s (ESA) Euclid space mission recently discovered an Einstein ring in a galaxy called NGC 6505, which is 590 million light-years away from Earth. While this sounds very far, in space terms, it is actually quite close.

In September 2023, astronomer Bruno Altieri first noticed the ring while studying a blurry image taken by the Euclid telescope. At that time, the telescope had only been in space for two months and was still being tested. Later, scientists took clearer pictures and confirmed that the ring was real. To honour Altieri, they named it Altieri’s Ring.

This ring was formed because light from another galaxy, which is 4.5 billion light-years away, was bent by the gravity of NGC 6505, the closer galaxy in front of it. This bending effect created the circular shape of the Einstein ring.

Why is this discovery important?

Altieri’s Ring is particularly exciting because it was found in a well-known nearby galaxy. So far, only five other gravitational lenses have been discovered at similar distances. This discovery shows how modern telescopes like Euclid can find new things even in well-studied parts of the sky.

Scientists are interested in Einstein rings for several reasons:

  • Studying the Universe’s Expansion: By analysing these rings, scientists can learn more about how the universe is expanding.
  • Testing Einstein’s Theory of Relativity: These rings provide an opportunity to test Einstein’s predictions about gravity.
  • Understanding Dark Matter: Dark matter is a mysterious form of matter that makes up about 30% of the universe but cannot be seen directly. Scientists can only detect its presence through its gravitational effects, like how it bends light in gravitational lensing.

How does gravitational lensing work?

Imagine you are looking through a magnifying glass at a small piece of text. The glass bends and enlarges the letters, making them easier to read. Similarly, a massive galaxy or galaxy cluster acts as a gravitational lens in space. When light from a distant object passes through this region, it gets distorted and sometimes multiplied, creating different shapes and patterns.

However, unlike a perfectly shaped magnifying glass, the gravitational lens can create multiple images of the same background object. The number and shape of these images depend on:

  • The distance between the observer, the lensing galaxy, and the background galaxy.
  • How well these objects are aligned.
  • The amount of mass present in the lensing galaxy.

An Einstein ring is a special case of strong gravitational lensing, where the background object is aligned almost perfectly behind the lensing galaxy, forming a complete or near-complete circle.

Future discoveries and euclid’s mission

Scientists discovered Altieri’s Ring very early in the Euclid mission. In March 2024, they used data from the Keck Cosmic Web Imager (KCWI) to confirm that the images were formed due to gravitational lensing (when light bends around a massive object).

To learn more, they also studied data from the Canada-France-Hawaii Telescope and the Dark Energy Spectroscopic Instrument. These observations helped them measure the mass and distance of both NGC 6505 (the closer galaxy) and the faraway lensed galaxy.

Their findings showed that the lensed galaxy is very old and no longer creates new stars.

While finding Altieri’s Ring is exciting, Euclid scientists caution that such a discovery is rare. In a paper published in Astronomy & Astrophysics on February 10, they noted: “… the exceptional nature of Altieri’s lens means it is unlikely that Euclid will find another lens” closer than around 680 million light-years “with a ring as bright as that observed here.”

Euclid officially began its sky survey on February 14, 2024, and is expected to discover around 100,000 new gravitational lenses throughout the universe. However, because closer galaxies are fewer, the chances of finding another Einstein ring so near to Earth are slim.

You might also be interested in: Who is Friedrich Merz? the man set to lead Germany as Chancellor