According to a news release from the European Space Agency’s Hubble Information Center, astronomers have discovered the most distant gravitational lens yet — a galaxy that, as foretold by Albert Einstein’s general theory of relativity, deflects and intensifies the light of an even more distant object. The finding offers a unique chance to directly determine the mass of a distant galaxy.

Light is influenced by gravity, and light passing a far-off galaxy will be deflected as a result. The first gravitational lens was discovered in 1979. Interestingly, gravitational lenses have several uses for astronomers. First, one can measure the mass of the matter that is bending the light. Second, the lens magnifies the background light source, giving astronomers a more detailed glimpse of distant galaxies than is normally possible.

Gravitational lenses are made up of two objects: one is further away and provides the light, and the other, the gravitational lens, which resides between us and the far-off light source, and whose gravity deflects the light. An Einstein ring is seen when the observer, the lens, and the distant light source are exactly aligned. An Einstein ring is a perfect circle of light that is the greatly magnified image of the distant light source.

“The discovery was completely by chance,” explained lead author Arjen van der Wel of the Max Planck Institute for Astronomy. “I had been reviewing observations from an earlier project when I noticed a galaxy that was decidedly odd. It looked like an extremely young galaxy, but it seemed to be at a much larger distance than expected. It shouldn’t even have been part of our observing program!”

Van der Wel began to examine images obtained by the Hubble Space Telescope. In these images the strange object appeared to be an old galaxy, but with some variable features which, he assumed, meant that he was staring at a gravitational lens. Combining the images and taking away the haze of the lensing galaxy’s group of stars, the outcome was very clear: a nearly perfect Einstein ring, implying a gravitational lens with very exact alignment of the lens and the background light source.

According to astronomers, the lensing mass is so far away that the light, after deflection, has journeyed 9.4 billion years to reach us.

The finding is a bit perplexing for astronomers. Gravitational lenses are the result of a chance alignment. However, in this particular case, the alignment is very precise. In addition, the magnified object is a starbursting dwarf galaxy. The likelihood that such a special galaxy would be gravitationally lensed is very small. Yet this is the second such galaxy that has been discovered to be lensed, meaning that astronomers have either been really lucky, or starbursting dwarf galaxies are a lot more common than previously believed.

“This has been a weird and interesting discovery,” van der Wel notes. “It was a completely serendipitous find, but it has the potential to start a new chapter in our description of galaxy evolution in the early Universe.”