Looking at this Hubble image, you might think it’s another run-of-the-mill yet spectacular spiral galaxy, nearly edge-on, with a pretty spiral in the background. But then you let your eyes scan down to the bottom…
Hey, what the heck is that giant green thing?
That, me droogs, is Hanny’s Voorwerp. Click the image to, um, to… envoorwerpenate.
OK, you ask, what’s a Voorwerp? Well, it’s Dutch for "thing". Doesn’t help much, though, does it?
All right then, let’s back up a bit: Hanny van Arkel, who discovered it, is not an astronomer. But she was reading a blog entry by Brian May, who is the guitarist for Queen as well as an astronomer. He had written about Galaxy Zoo, a project where you can classify galaxies on your computer. Being a Queen fan, Hanny checked it out, and started looking at galaxies… which is how she found this weird green smear of light. She asked about it, and astronomers took interest… and the result is this amazing Hubble image of a very odd object.
What is it? Well, the green color is a dead giveaway that it’s a giant cloud of gas; the green comes from glowing oxygen, spread ethereally thin. The nearby galaxy must be involved, as there’s no other source of illumination, which in turn means this thing is pretty big. In fact, it’s the same size as our galaxy, 100,000 light years across!
The thinking is that there is a supermassive black hole in the center of that galaxy (which is named IC 2497). For a long time, that black hole was swallowing down material, and it turns out to have been a sloppy eater: as material falls in, it piles up in a disk outside the Final Plunge. This disk heats up, and various forces can combine to create huge jets of energy and matter that scream out in opposite directions.
At the same time, well outside the galaxy, there is a stream of gaseous material hundreds of thousands of light years long that was basically minding its own business. Then one of these beams of energy from the center of IC 2497 slammed into it, lighting it up and making it glow like a neon sign.
But there’s also matter in those beams, and that has apparently compressed the tip of the Voorwerp on the side facing the galaxy (facing upwind, if you like). In the image, you can see how the tip is yellow; that light is coming from stars that are forming as the gas is compressed. These stars are being born well outside the galaxy itself! What a view any potential future civilizations will have: an almost entirely black sky, with a giant galaxy hanging there looking down on them. They’ll have interesting mythology, I’d wager.
Anyway, at some point, maybe 200,000 years ago, the material going into the black hole at the heart of IC 2497 choked off. Maybe the material just ran out, the last of it falling into the hole. When that happened, the searchlight beams shut off. The Voorwerp is still glowing, because it takes thin gas a long time to lose its glow, but eventually it’ll stop glowing too.
When I first saw the image, I thought the Voorwerp was cone-shaped, like a megaphone pointed a bit away from us. That circular hole was what gave that impression, but my old friend Bill Keel, an astronomer involved with this observation, speculates it may be a shadow of some object near the black hole, like "a fly on a projector". There’s material there, but we don’t see it lit up because it’s in a shadow. Bill thinks this may be the case because there’s no other obvious way to create a big hole like this in the material itself; an explosion or wind from a star would have to be titanic to create such a hole, and there’s no apparent streamers or filaments you’d expect to see.
Scientifically, this is a fantastic object. Nothing like this has been seen before, so everything we learn about it is new. But the other story is equally wonderful. I’ve shown a picture of Hanny here, because I want you to see that she is what is known in the über-geek world as "a normal person". She’s a school teacher, and liked music, specifically Queen (a woman of excellent taste). Because she liked Brian May, and Brian wrote about Galaxy Zoo, she discovered this object. You can read about it in her own words on her website, in fact.
The thing is, she liked science. She wasn’t an astronomer beforehand — I suspect she has a pretty good grasp of it now! — but decided to try her hand at identifying galaxies. And now she’s deservedy famous; she discovered something no one had ever seen before, and even with Hubble observations still leaves quite a bit to be understood.
I love citizen science projects like Galaxy Zoo and its offshoots. It doesn’t always take a degree, or years of training, to make an impact of science.
All it takes is interest. That can lead to love, and a degree, and training… or just to more interest. But clearly, that can be enough.