It is so extraordinary that it has been given its own name.
A rare and unusual phenomenon was recently discovered by doctoral student Margherita Bettinelli of the Instituto de Astrofísica de Canarias (IAC) and the University of La Laguna (ULL), alongside an international team of astrophysicists of the Stellar Populations group at the IAC. The astronomical object? An Einstein ring.
But this is no ordinary Einstein ring. In fact, it is so unique that it has been given its own name: “The Canarias Einstein ring.”
An Einstein ring is a contorted image of a very distant galaxy, known as “the source.” When there is a massive galaxy between the source and the observer — us here on Earth — this massive galaxy, called “the lens,” bends the light rays emitted from the source.
Since the lens galaxy is so enormous, it has a strong gravitational field that warps the structure of space-time around it, which not only attracts objects with mass but also bends the paths of light. When the source galaxy and the lens galaxy are exactly aligned, the image of the more distant galaxy is transformed into an almost perfect circle surrounding the lens galaxy. If the galaxies are a little off in their alignment, there are irregularities in the circle.
Bettinelli spotted the Einstein ring while analyzing data of the Sculptor dwarf galaxy — a close neighbor of our Milky Way — from the Dark Energy Camera (DECam) of the 4-meter Blanco Telescope at the Cerro Tololo Observatory, located in Chile. After alerting her colleagues, the team began to observe the object's physical properties with the OSIRIS spectrograph on the Gran Telescopio CANARIAS (GTC).
Excitingly, the Einstein ring was confirmed. But what’s more, the “Canarias Einstein ring” is the most symmetric ever discovered. In fact, it is almost circular, which means that the two galaxies are almost perfectly aligned.
The source galaxy is 10 billion light-years away from us. Interestingly, due to the continuous and accelerated expansion of the universe, the distance between us and the source was actually smaller when its light first started its journey toward Earth. What this means is that it has taken the light 8.5 billion years to reach us, and we are observing it how it was back then — a blue galaxy which is just beginning to evolve and with lots of stars forming. However, just like the lens galaxy that is located a little closer to us at 6 billion light-years, its population of stars are now likely red and old.
"Studying these phenomena gives us especially relevant information about the composition of the source galaxy, and also about the structure of the gravitational field and of the dark matter in the lens galaxy," explained Antonio Aparicio, one of the IAC astrophysics leading the research, in a press release.
The results are published in the journal Monthly Notices of the Royal Astronomical Society.
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