The Hubble Space Telescope has found the farthest known specimen of a cosmic "magnifying glass" known as a lensing galaxy detected to date, astronomers say.

The elliptical galaxy is so big its magnifying quality has revealed the light of another faint galaxy behind it and allowed them to gaze some 10 billion back into the universe's past, the astronomers say.

The extreme gravitational field of lensing galaxies means they can magnify light emitted by galaxies even farther away that might otherwise be undetectable in astronomical observations.

The newly identified galaxy, seen by Hubble and confirmed by the Hawaii's Keck Observatory, has revealed the light coming from an even more distant galaxy just behind it located 10.7 billion light years away from us.

It's rare to discover a lensing galaxy that's so remote but also aligned so perfectly with another located behind it that it can reveal its light, the researchers say.

"When you look more than 9 billion years ago in the early universe, you don't expect to find this type of galaxy lensing at all," explains lead researcher Kim-Vy Tran of Texas A&M University. "It's very difficult to see an alignment between two galaxies in the early universe."

The galaxy the cosmic lens has revealed is a small spiral one displaying signs of the rapid formation of new stars.

The lensing galaxy, part of a galaxy cluster identified as IRC 0218, is 200 million light years farther away than the previous farthest ever seen, the astronomers say.

Since the first lensing galaxy was identified in 1979 hundreds have been detected, but none this far away, they note.

"There are hundreds of lens galaxies that we know about, but almost all of them are relatively nearby, in cosmic terms," says study first author Kenneth Wong of the Academia Sinica Institute of Astronomy & Astrophysics in Taiwan. "To find a lens as far away as this one is a very special discovery because we can learn about the dark-matter content of galaxies in the distant past."

Dark matter, invisible but detectable from its gravitational effects, is thought to make up most of the universe's mass.

It's not just its distance that makes the newly discovered galaxy interesting, the researchers say, but also its immense size at 9.6 billions years ago, the age we are seeing it as from its light arriving at Earth now.

"Even though this object is smaller than the Milky Way [is] now," Tran says, "you're seeing it when the universe was much younger. If you could see the Milky Way at the same time, it would be much, much smaller than it is today."

Since astronomers are observing it as it existed nine billion years ago, the researchers say, they are getting an intriguing peek into the universe's past and into the processes of galaxy formation.