London | Scientists have discovered one of the most symmetrical Einstein rings – a rare astronomical phenomena – created by a galaxy located 10,000 million light years away that is hidden behind a more massive galaxy.
Einstein rings, predicted by Einstein’s theory of General Relativity, are quite rare but scientifically interesting. The one discovered by Instituto de Astrofisica de Canarias (IAC) and the University of La Laguna (ULL) in Canary Islands is named the The Canarias Einstein ring.
An Einstein ring is a distorted image of a very distant galaxy, which is termed the source. The distortion is produced by the bending of the light rays from the source due to a massive galaxy, termed the lens, lying between it and the observer.
The strong gravitational field produced by the lens galaxy distorts the structure of space-time in its neighbourhood, and this does not only attract objects which have a mass, but also bends the paths of light. When the two galaxies are exactly aligned, the image of the more distant galaxy is converted into an almost perfect circle which surrounds the lens galaxy. The irregularities in the circle are due to asymmetries in the source galaxy.
The chance discovery was made by Margherita Bettinelli, of IAC when she was examining data taken through the Dark Energy Camera (DECam) of the 4m Blanco Telescope at the Cerro Tololo Observatory in Chile. She was analysing the stellar population of the Sculptor dwarf galaxy and noticed the peculiar morphology of the Einstein ring.
Researchers then started to observe and analyse its physical properties with the OSIRIS spectrograph on the Gran Telescopio CANARIAS (GTC). This Canarias Einstein ring is one of the most symmetrical discovered until now and is almost circular, showing that the two galaxies are almost perfectly aligned, with a separation on the sky of only 0.2 arcseconds, researchers said.
The source galaxy is 10,000 million light years away from us. Due to the expansion of the universe, this distance was smaller when its light started on its journey to us, and has taken 8,500 million years to reach us. We observe it as it was then: a blue galaxy which is beginning to evolve, populated by young stars which are forming at a high rate.
The lens galaxy is nearer to us, 6,000 million light years away, and is more evolved. Its stars have almost stopped forming, and its population is 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, said Antonio Aparicio, one of the IAC astrophysicts, who led the research.