1. What’s large and blue and can wrap itself around an entire galaxy? A¬†gravitational lens¬†mirage.¬†Pictured above, the gravity of a luminous red galaxy (LRG) has¬†gravitationally distorted¬†the light from a much more distant blue galaxy. More typically, such light bending results in¬†two discernible images¬†of the distant galaxy, but here the¬†lens alignment¬†is so precise that the background galaxy is distorted into a horseshoe — a nearly complete ring. Since such a¬†lensing effect¬†was generally predicted in some detail by¬†Albert Einstein¬†over¬†70 years ago, rings¬†like this¬†are now known as¬†Einstein Rings. Although LRG 3-757 was discovered in 2007 in data from the¬†Sloan Digital Sky Survey¬†(SDSS), the image shown above is a follow-up observation taken with theHubble Space Telescope's¬†Wide Field Camera 3. Strong gravitational lenses like LRG 3-757 are more than oddities — their multiple properties allow astronomers to determine the mass and¬†dark matter¬†content of the foreground galaxy lenses.

     
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