by Ann Finkbeiner
Hanny’s back, this time with a plausible story. Back in 2007, Hanny van Arkel, a Dutch schoolteacher, was on her computer happily classifying galaxies on Galaxy Zoo and was about to click Next, when she thought, “Wait. What was that?” At first, nobody knew: it was green, it glowed, it was shapeless, they called it Voorwerp.
Eventually, after astronomers burned up telescope time looking at the Voorwerp in optical, radio, ultraviolet and xrays, they decided it was a blob of gas whose oxygen — oxygen is green, you know that, don’t you — was being lit up by something going on in a nearby galaxy with the unforgettable name of IC 2497. Finally astronomers got time on the Hubble Space Telescope (which is a little like getting time with the Pope) and have not only taken this pretty picture, they think they have the story.
IC 2497 isn’t the innocent, uninteresting little spiral galaxy they thought. It’s skewed and it’s violent. Another galaxy collided with it, and the collision riled up a lot of messy gas, some of which got warped into a long, invisible tail around IC 2497, and some of it got pulled into IC 2497’s center where unbeknownst lurked a dead black hole. The black hole came alive, sucked in the gas, lit up, and sent out a jet of high-energy light that turned a part of the long tail green and made the Voorwerp. A little later, shock waves in the gas hit the Voorwerp and created small, yellow-orange stars in it. As fireworks, it must have been spectacular: CRASH, whoooosh, ssssss, BLAMMO, WHAM, tinkle, tinkle, tinkle.
After it was all over, IC 2497’s black hole went back to sleep.
About the only thing left to figure out is why the Voorwerp seems to have a hole in it and why the hole’s edges are so smooth: maybe it’s really a shadow. Maybe when the black hole was active, its light got blocked by something nearby, and I’d rather not think about it. Meanwhile, at the astronomical conference where all this is being announced, Hanny remains her own natural self, being treated like a movie star, getting interviewed by the media, and feeling silly about it all.
Ann Finkbeiner is a coproprietor of The Last Word on Nothing.