Solving the cosmic mystery of the green blob in spaceS

Back in 2007, Dutch schoolteacher and amateur astronomer Hanny van Arkel spotted a strange object near a distant spiral galaxy...and nobody had any idea what it was. Now, four years later, we're finally learning the truth about this mysterious object

Hanny's Voorwerp - which is simply Dutch for "Hanny's Object" - confounded astronomers when van Arkel first brought it to their attention in 2007. They knew it was a massive green blob in space, but that was pretty much it, as nothing like the object had ever been seen before. Hubble has now been able to discover active star birth in a part of Hanny's Voorwerp that faces the nearby spiral galaxy IC 2497, located about 650 million light-years from Earth.

The galaxy's gas is trickling out across the cosmos to the object, fueling continued star formation. Most of the stars are born in one particular small region of Hanny's Voorwerp, and this area is collapsing as more and more stars form. Indeed, galaxy IC 2497 has long been meddling in the affairs of Hanny's Voorwerp. The black hole at the center of the galaxy likely created a quasar, an intense light beacon that shot towards the object, giving the gas cloud its strange green glow. Hanny's Voorwerp is green because it has lots of oxygen molecules inside it, which are turned green in the incredibly bright light.

Astronomer William Keel explains what's going on here:

"The star clusters are localized, confined to an area that is over a few thousand light-years wide. he region may have been churning out stars for several million years. They are so dim that they have previously been lost in the brilliant light of the surrounding gas. We just missed catching the quasar, because it turned off no more than 200,000 years ago, so what we're seeing is the afterglow from the quasar. his implies that it might flicker on and off, which is typical of quasars, but we've never seen such a dramatic change happen so rapidly."

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.

The current galaxy IC 2497 is likely the result of a merger about a billion years ago, a cataclysmic event that funneled tons of gas and matter into the central black hole. The fattened black hole then kicked off the quasar, which shot material out into what is now Hanny's Voorwerp. The stars in the object are now being born outside any galaxy, meaning any future civilizations living around one of those stars will have one of the most insane views in the cosmos - an almost starless night sky, with the view dominated by the hulking view of galaxy IC 2497, the far distant object that made their existence possible.

[Hubble; check out Bad Astronomy for more on the object's discoverer]