At first glance, this Hubble image looks like a tiny arrangement of lights hung around two galaxies. Look again, and it becomes a puzzle: some of those lights are the same object appearing in different places.
The image shows a gravitational lens involving the distant quasar 2M1310-1714. Two galaxies in front of it bend the paths of its light toward us. The result is four conspicuous quasar images around the central pair, plus a much fainter fifth image near the middle. One quasar, five appearances—and a beautiful reason to be careful when counting objects in a space photograph.
The smaller-scale lensing connection
The same gravitational principle also helps astronomers search within the Milky Way for objects that are difficult to see directly. With microlensing, an intervening object can briefly magnify the light of a background star. Astronomers follow changes in that star’s brightness and, where measurable, its apparent position; they do not need a resolved photograph of a ring.
NASA’s Hubble account of an isolated dark stellar remnant explains how this approach can help identify a stellar-mass black hole. NASA’s explanation of rogue-planet searches describes the corresponding use for planets drifting without a host star. The lens need not shine to leave a measurable effect on someone else’s light. These examples span very different scales. A planet passing in front of a distant star may reveal itself through a temporary change in brightness, while the foreground galaxies in this Hubble view produce several resolved images. The observations look different because the masses, distances and alignments differ.
What are we actually looking at?
ESA/Hubble released the observation on August 9, 2021, under the title “Seeing Quintuple”. Its description separates the two foreground galaxies from the multiple images of the background quasar. The fifth quasar image is faint enough that it should not be expected to leap out of a small web reproduction.
The wider view and enlargement above show the same system. The enlargement helps us inspect the arrangement; it does not add another group of objects. The central galaxies really are separate galaxies, whereas the surrounding quasar images are different views of the same distant source.
How gravitational lensing makes extra images
Einstein’s general theory of relativity describes gravity in terms of curved spacetime. A sufficiently massive object can bend the apparent path of light travelling past it. If a bright object lies farther away along a suitable line of sight, its light can reach us by different routes around the intervening mass.
We then see the background source displaced, stretched or repeated. No glass lens is involved: the foreground mass does the work. ESA/Hubble’s gravitational-lensing guide explains how the same effect can magnify distant sources, making details easier for a telescope to study.
A useful way to read the picture is to think in depth. Start with the observer, move out to the foreground galaxies, and then continue much farther to the quasar. A photograph compresses that long journey into a flat frame. Objects that appear close together on the image need not be neighbours in space.
Why is it called an Einstein ring?
When the foreground lens and background source line up closely enough, the distorted background light can form a ring. With other alignments or mass distributions, the pattern can be incomplete arcs or separate images. The shape is part of the information astronomers investigate.
The 2021 picture is often shared under the broad “Einstein ring” description, but its most useful feature to understand is the repeated quasar. The bright points around the central pair are not stars sitting on a physical hoop. Nor is there a glowing circular structure linking all of the apparent points together in space.
The distinction is easy to miss because the image is so pleasingly arranged. Understanding the geometry makes it more remarkable: a distant light source and the gravity of intervening galaxies have produced a pattern we can study from Earth.
What is a quasar?
A quasar is an exceptionally luminous galactic nucleus powered by material falling toward a supermassive black hole. Gas in the surrounding accretion flow releases enormous amounts of energy before reaching the black hole. The light we observe is not escaping from inside the black hole itself.
That concentrated brightness helps explain why a quasar can appear as a compact point even though it belongs to a much larger galactic system. ESA/Hubble’s quasar guide places these objects within the broader family of active galactic nuclei.
What can astronomers learn from the distortion?
A gravitational lens provides more than an attractive image. Magnification helps researchers examine a background source, while the way its light is distorted gives clues to the foreground mass responsible. ESA describes strong lenses as tools for investigating dark matter and the wider Universe in its account of Euclid’s Einstein-ring discovery.
This is a good example of an astronomical measurement needing interpretation. A bright spot is an observation; deciding which source produced it requires a model of the system. The eye notices a pattern first. Researchers then test whether a physical explanation can account for it.
There is a useful comparison with Kepler’s discoveries of planets around other stars. Kepler’s transit method looks for dips in starlight when a planet crosses a star. Gravitational lensing instead examines how intervening mass changes the appearance or brightness of a background source. Both turn changes in light into evidence, through different physical effects.
A newer Einstein ring found by Euclid
On February 10, 2025, ESA announced a different example: a remarkably complete Einstein ring around the nearby galaxy NGC 6505. The ring is the distorted image of a much more distant background galaxy, revealed in observations from the Euclid mission.
This is a separate system from Hubble’s 2M1310-1714 quasar lens. Placing the discoveries side by side shows why there is no single appearance that every gravitational lens must share: one offers a striking ring, while another makes a distant quasar appear several times.
Next time a space image seems to contain an impossibly neat arrangement, pause before counting. Some of its beauty may come from the journey the light has taken.
Closer to an event horizon, X-ray echoes from the far side of a black hole’s accretion disk offer a different test of how gravity changes light’s path.
A practical starting point is the image caption: check which lights belong to the lens and which are repeated images of the background source. Then compare the wider view with the enlargement. Enlarging an image changes how easily you can inspect it; gravitational magnification occurs along the light’s journey, before that light reaches the telescope.
Hubble’s view of the quasar lens
Further reporting: Science Alert.
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