Figure 1 . Color images of six strong lenses confirmed with Gemini South spectroscopic follow-up : a ) DES J0221-0646 , b ) DES J0250-0008 , c ) DES J0329-2820 , d ) DES J0330-5228 , e ) DES J0446-5126 , f ) DES J2336-5352 . Each of these systems is a galaxy group or richer cluster , but just one or a few galaxies near the center of the cluster cause most of the lensing . ( All figures reproduced from Nord et al ., 2016 .)
Finding and confirming candidates are the first steps in measuring cosmic structure and dark energy with strong lenses . The results will help us to understand why the Universe is accelerating and not being slowed by the mass it contains .
When Space Gets Warped
One maxim of Einstein ’ s Theory of General Relativity is that space-time — the concept that space and time are one — tells energy how to move , and energy tells space-time how to curve . Gravitational lensing demonstrates both of these concepts : the path of light traveling from a distant object ( like a galaxy ) is deflected by a depression in the fabric of space-time caused by a massive object nearer to us . The more massive this intervening lensing object , the larger the crater , and the more distorted the observed image of the distant source galaxy .
Gravitational lenses act like terrestrial lenses made of plastic or glass , bending light in ways we can model well with geometric optics ; the equations have multiple simultaneous solutions , which describe the different paths light can take from a single source , as well as the amount of magnification in the lensed image . A single source galaxy can appear highly magnified and have multiple images — both telltale signatures of a strong lensing system .
What Can Strong Lenses Tell Us about the Universe ?
With strong gravitational lensing we can examine in detail galaxies normally too faint to observe . The observations also provide an avenue for studying galaxy evolution at epochs earlier in the Universe than would be available otherwise . The total lensing mass and its spatial distribution dictate the morphologies of lensed images . By measuring the amount and type of distortion of the source image , we can learn more about the mass distribution ( including that due to dark matter ) in the lensing galaxies or clusters .
Moreover , particular configurations of lenses can help constrain dark energy models . In systems with two or more source galaxies
12 GeminiFocus January 2017 | 2016 Year in Review