Imagine seeing light from deep space bent into a thin, distinct ring by the curvature of spacetime as it wraps itself around an enormous object like a galaxy or galaxy cluster.
Sounds like science fiction, doesn't it?
Yet that’s exactly what the Hubble Space Telescope has captured in a this image: a distinct, glowing halo of light called an 'Einstein ring', created by a phenomenon that was theorised by Albert Einstein over 100 years ago.
What Is an Einstein Ring?
An Einstein ring isn’t a product of science fiction; it's science fact. It’s a rare, remarkable consequence of Einstein’s general theory of relativity.
According to Einstein, massive objects like galaxies and galaxy clusters warp the fabric of spacetime around them.
So when light from a distant galaxy reaches our telescopes, but has encountered another galaxy on its journey, that light doesn’t move in a straight line.
It bends around the closer galaxy like the beam from a torch curving around a bowling ball.
The effect is known as gravitational lensing, which can magnify light from the background object, acting as a cosmic magnifying glass that enables astronomers to see details that otherwise would be too faint.
And if the alignment of the background object, foreground object and Earth is just right, the light bends into a circle or an arc around the foreground galaxy.
This glowing halo of light is known as an Einstein ring, in honour of Einstein's work predicting the phenomenon.
Depending on the precision of the alignment, we might see a full circle or a partial one.
Either way, it’s a cosmic spectacle.
A closer look at HerS 020941.1+001557
The Einstein ring in this Hubble image is one of many that have been captured since the first one was seen in 1987 with the Very Large Array network of radio telescopes in New Mexico, named MG 1131+0456.
In the Hubble image here, the red arc is light from a galaxy known as HerS 020941.1+001557, located 19.5 billion lightyears away.
Those aware that the Universe is 13.8 billion years old may be baffled by that number: how can light have been travelling for longer than the age of the cosmos?
Here’s the twist: the light we’re seeing was emitted 11 billion years ago, when the galaxy was 5.5 billion lightyears away, but the Universe has expanded in the time it's taken for that light to get to us
We’re seeing the light as it looked when the Universe was less than a quarter of its current age.
The elliptical galaxy doing the lensing, and responsible for creating the Einstein ring, is SDSS J020941.27+001558.4, much closer at 2.7 billion lightyears from Earth.
It acts like a magnifying glass, bending and amplifying the light from the more distant galaxy.
The result is this warped, magnified and spectacularly curved arc of light: an Einstein ring.
A third galaxy, SDSS J020941.23+001600.7, appears to intersect the ring, adding more visual drama to the scene.
This Einstein ring was identified by a citizen scientists through a project called SPACE WARPS, which invites the public to help search images for gravitational lenses.
Why Einstein Rings matter
Einstein rings are visual evidence of a mind-blowing theory in physics.
They help astronomers study the distant galaxies whose light is lensed, but also the foreground galaxies doing the lensing.
Gravitational lensing allows researchers to study galaxies that would otherwise be too faint or distant to detect.
How much the light is bent by the foreground object gives astronomers information about the size and mass of that foreground object.
And because galaxies and galaxy clusters contain so much dark matter – the invisible substance holding most of the Universe together – gravitational lensing and Einstein rings provide clues helping astronomers investigate what dark matter could be.
