Astronomy Picture of the Day

Explanation: What's large and blue and can wrap itself around an entire galaxy? A gravitational lens mirage. Pictured here, the gravity of a massive elliptical galaxy (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: an Einstein ring. 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 the Hubble Space Telescope's Wide Field Camera 3. A recent lens analysis of the central galaxy indicates that it likely hosts the single most massive black hole yet discovered: 36 billion times the mass of our Sun.