Keren Sharon
Probing Time Delays in a
Gravitationally Lensed Quasar
Fast Turnaround observations with the Gemini North telescope
are used to measure the difference in the arrival time of photons
coming from a distant quasar, as they travel on different paths
from the quasar to us due to gravitational lensing. The Gemini
observations also produced deep spectroscopic data with GMOS
that allowed our research team to obtain redshifts for other lensed
galaxies behind the cluster.
Imaging data from the Sloan Digital Sky Survey (SDSS) has uncovered many gravitational
lenses including SDSS J2222 + 2745 — a galaxy cluster whose projected mass density is high
enough to bend space-time, causing light traveling near it from a distant quasar to change
its path. This phenomenon, which is a theoretical prediction of General Relativity, is called
gravitational lensing.
Describing a Strong Gravitational Lens
When we observe massive objects, such as galaxy clusters, we often find that distant background galaxies appear distorted and stretched, and their apparent position in the sky is different than their actual positions.
The equations that describe gravitational lensing dictate by how much the light is deflected due to the gravitational potential of an intervening object. The more massive an astronomical object, the stronger its lensing potential, and the larger the deflection of light. In
some cases, which we call Strong Lensing (SL), there is more than one solution to the lens-
January 2016
GeminiFocus
3