It sounds like something out of one of Douglas Adams’ Hitchhiker’s novels: a giant green cloud of gas known as Hanny’s Voorwerp that, by all appearances, is about to devour a nearby galaxy. So what is it? Well, astronomers aren’t exactly sure, but they have a pretty good idea, and this image – the most detailed to date, courtesy of Hubble – is helping them shed more light on the strange cosmic feature.
But let’s back up: Voorwerp is not a word borne of an alien tongue, but means “thing” or “object” in Dutch. And who is Hanny? She’s the Dutch schoolteacher and non-astronomer who discovered the Voorwerp lurking outside of galaxy IC 2497 via Galaxy Zoo, an online project where amateur stargazers can help classify galaxies by their shapes. Hanny van Arkel took an interest in the smear of green she spotted hovering near IC 2497, which in turn sparked astronomers’ interests as well, though they couldn’t explain it at the time.
Now Hubble is on the case, giving astronomers an enhanced view of her Voorwerp (not that Voorwerp, pervert), and the thinking now goes as follows: The green wispy structure is a giant cloud of gas, but that wasn’t the difficult part to hammer down. What puzzled astronomers was the source of light that makes the cloud glow. One idea involved a quasar in the nearby galaxy supplying the gas with light, but no quasar could be found. No other light souces was readily apparent, either.So now the theory has shifted to that of a supermassive black hole in the center of IC 2497 that swallowed material for eons, leading to the creation of a huge energy jet that then blasted outward and connected with the nearby gas, lighting it up. Then, at some point many tens of thousands (or even hundreds of thousands) of years ago, the black hole ran out of material to swallow, or perhaps it shifted the way it gives off energy.
Whatever the case, it is no longer bombarding the gas cloud with energy – hence, no apparent light source. The Voorwerp continues to glow because it takes thin gas like the kind found there a long time to stop glowing. Eventually, starved of some kind of energy, Hanny’s Voorwerp will voorwerp no more.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.


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Oh my stars! Why couldn't the nearby galaxy be the source of light? The cloud seems to turn a lighter green the closer it gets to the galaxy. Does the Hubble shoot in 3D? They need to get on that.
One of the many mysteries of the universe. It will probably never be solved, and if it is, that conclusion will be re-written in 50 years.
When the picture was small, the green gas looked like a tree.
Made me wonder what was with the nearby galaxy.
It's Galactus...
Its staring us in the face. It is an intelligent form of life migrating to a new galaxy. Its not gas, its actually a bunch of small ships.
Would be neat if it turned out to be a substance we could use for fuel in deep space flight.
It looks like it is either an intergalactic fart...
... or someone peed in the cosmic pool.
@nonethewiser I'm pretty sure that the hubble telescope wouldn't be able to see in 3D, which is too bad, cause that would be awesome! since the objects it focuses on are so far away, it would be incredibly hard to get two different perspectives of the same object- the two lenses for the telescope would have to be REALLY far apart. but i could be wrong... you can never say never