Solving the Voorwerp Mystery

io9 wrote Solving the cosmic mystery of the green blob in space "As strange as Hanny's Voorwerp first appeared, it's actually part of something much larger and more bizarre. It looks like a giant green space blob, but it's actually just one part of a massive, 300,000 light-year long ring that stretches around the entirety of galaxy IC 2497, and we were only able to see any part of it because the quasar was pointed in the right direciton. The ring isn't just long, it's also unimaginably thick - astronomers estimate Hanny's Voorwerp covers all the sapce 44,000 to 136,000 light-years from the galaxy's core."

HubbleSite has more details and a great picture by Hubble.