Scientists discover ‘Einstein ring’ around nearby galaxy: What it is, its significance

Sub: Sci

Sec: Space sector

Context:

In September 2023, the European Space Agency’s (ESA) Euclid space telescope made an extraordinary discovery of a rare phenomenon known as an Einstein ring. This ring of light surrounds the galaxy NGC 6505, located 590 million light-years away from Earth.
The images were released to the public in February 2025, showcasing a bright ball of light at the centre with a cloudy ring surrounding it.

What is an Einstein Ring:

An Einstein ring is a ring-like structure formed when light from a distant galaxy or celestial object is bent and magnified by a massive object, such as another galaxy, cluster, or dark matter. This occurs due to a process known as gravitational lensing.
Einstein rings are extremely rare, with fewer than 1% of galaxies exhibiting such a phenomenon.
They are named after mathematician and physicist Albert Einstein. His general theory of relativity predicted that light could bend and brighten around objects across the cosmos.
The first Einstein ring was discovered in 1987, and since then, more have been found, but their exact number in the universe remains unclear.
They are not visible to the naked eye and can only be observed through space telescopes, such as Euclid.

Formation of an Einstein Ring:

Normally, light from distant sources travel in a straight line towards Earth. However, if a large galaxy lies between the light source and Earth, its immense gravitational field can bend the path of the light.
The foreground galaxy then acts as a “gravitational lens,” focusing the light from the background galaxy and distorting it into a highly magnified, ring-shaped image.
For an Einstein ring to form, there needs to be a massive galaxy in the foreground that can bend the light. Additionally, the foreground galaxy must be precisely aligned with the background galaxy from the perspective of the telescope observing them. Only under these ideal conditions can the gravitational lensing effect create the distinct ring-shaped image of the distant galaxy.

Gravitational Lensing:

Gravitational lensing happens when a massive object distorts the fabric of space-time and bends light traveling from a distant source. The object creating the distortion is called the gravitational lens.
In the case of the Einstein ring discovered around NGC 6505, the galaxy itself acted as the gravitational lens, bending and amplifying the light from a more distant galaxy located 4.42 billion light-years away.

Significance of Einstein Rings:

Einstein rings are crucial for understanding various cosmic phenomena, especially the mysterious dark matter.
Dark matter is thought to account for 85% of the total matter in the universe, but it cannot be directly observed since it does not interact with light.
Gravitational lensing, including Einstein rings, provides scientists with a means of detecting and studying the effects of dark matter indirectly through its gravitational influence.
They also help study distant galaxies that would otherwise be invisible due to their great distance and gain insight into the expansion of the universe, as light from distant galaxies stretches over time due to cosmic expansion.

About Euclid telescope:

Euclid is a space telescope launched by the European Space Agency (ESA) to study the geometry of the universe and dark energy. It was launched in July 2023.
Euclid is named after the Greek mathematician Euclid of Alexandria, who lived around 300 BC and founded the subject of geometry.
Euclid is designed to explore the evolution of the dark Universe. It will make a 3D-map of the Universe (with time as the third dimension) by observing billions of galaxies out to 10 billion light-years, across more than a third of the sky.
It will remain operational for a minimum of six years.