Doug's Darkworld

There it is, a mysterious green blob in deep space. I wasn’t kidding. OK, maybe I exaggerated a little bit. What is it? No one knows. Is it a danger to Earth? Probably not, it’s about 700 million light years away. Normally when one tosses off huge astronomical distances, they get qualified by “that’s actually pretty close in cosmic terms.” In this case, no, 700 million light years is actually a pretty fair distance away. The nearest galaxy to Earth is some 2.5 million light years away, this puppy is nearly 300 times as far away as that. At the time the light from this image started on its way to Earth, there was only the most primitive life in the sea, small worms and such, and nothing more than microbes on land. And all the continents were pretty much gathered together in one big lump.

The mystery green object is called Hanny’s Voorwerp. It was discovered by Dutch school teacher Hanny van Arkel in 2007. How the heck did a school teacher discover an object 700 million light years away? I mean, this is a picture taken by a 2.5 metre telescope,  it’s not something one can see with even the finest backyard telescope. Well, she was an amateur volunteer in the Galaxy Zoo project. What is the Galaxy Zoo project? It’s pretty simple really, this 2.5metre telescope was used to photograph much of the sky in something called the Sloan Digital Sky Survey. Literally millions of galaxies were photographed, far beyond what the world’s astronomers could examine. So millions of human volunteers were enlisted to download pictures from the sky survey and pore over them to identify the galaxies and other oddities. Yes, turns out the human brain is still pretty damn useful, especially when millions of them are harnessed. The project was big success, it determined some new information about the universe, and even led to the discovery of a new class of galaxy. And lastly, to the discovery of Hanny’s Voorwerp.

So what the hell is Hanny’s Voorwerp? (Voorwerp is Dutch for object by the way.) No one knows for sure. It’s the same distance away as the otherwise unremarkable spiral galaxy IC 2497 next to it. It does seem clear that it is something called a reflection nebula. A reflection nebula is where interstellar gas, in this case possibly a deformed dwarf galaxy, reflects the light of some nearby object rather than generates the light itself. The other type of nebula is an emission nebula, where the gas itself has been so heated up that it is emitting light. A gallery of reflection nebula can be seen here.  I haven’t been able to track down exactly how astronomers are able to determine one from the other, I assume it has to do with the exact nature of the light coming from the nebula.

OK, so its a bunch of gas reflecting the light from some green light source? What’s so weird about that? Well, two things. For one thing, it’s green. Reflection nebula are either red or blue, no one has ever seen a green one before. So there is either something highly unusual about the nebula itself, or something odd about the source of the light that is being reflected. And that brings us to the second thing odd about this, notice any brilliant green light near Hanny’s Voorwerp? The only thing bright enough to light up something that size would be a quasar, a huge black hole at the centre of galaxies. Well, galaxy IC 2497 doesn’t appear to have  a quasar at its centre.

Are there any theories at all? Well, sort of. It’s possible that there was a quasar at the centre of galaxy IC 2497, but that for whatever reason it stopped emitting light some thousands of years ago, but the light it previously emitted is still hitting Hanny’s Voorwerp. It’s kind of a stretch, but it at least is possible. The colour though, that’s harder to explain. What scientific speculation along those lines I can find is beyond my ken, here’s a site that covers it but it’s pretty much Greek to me. And while most of the pics on the site show Hanny’s Voorwerp in blue, never fear, near the bottom they explain that in visible light, it would indeed appear green. The only thing that can be said for certain is that Hanny’s Voorwerp is very unusual, and it is continuing to get a lot of study.

No big lesson here, other that my oft repeated axiom that the Universe will always hold surprises for us. British astronomer Sir Arthur Eddington (18882-1944) put it best when he said “Not only is the universe stranger than we imagine, it is stranger than we can imagine.”

(The above image  is licensed by the Galaxy Zoo under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.0 UK: England & Wales License. Credit and copyright: Galaxy Zoo. Coming soon, as a gentle reader reminded me, how scientists are going to weigh tiny pebbles to search for God. And yes, that’s a little bit of an exaggeration, but in this case, the reality is even stranger than the exaggeration.)