Schoolteacher Discovers "Voorwerp"

"What is a Voorwerp" you ask? Great name for a strange something near another galaxy.

Okay, let's start with the discovery. The Sloan Digital Sky Survey (SDSS) is a massive project to map about 1/4 of the night sky and has been taking data since 1999 and just finished (last month!) In the interest of disclosure, I spent a year working on it as part of a fellowship at Fermilab.

The SDSS saw lots of galaxies, hundreds of millions. Computers are pretty lousy at figuring out if the galaxy is a spiral, elliptical, irregular, etc. so they set up a website called Galaxy Zoo (and in the interest of more disclosure, I know most of the Galaxy Zoo team and give workshops to teachers at meetings such as the National Science Teachers Association on how to use Galaxy Zoo with students). The idea of galaxy zoo is to train a lot of amateur astronomers and let them classify galaxies. It has been a rousing success as tens of thousands of people have classified each of the initial batch of 800,000 galaxies...just to check and be sure they get it right, each galaxy has been looked at by an average of 40 different people (for a whopping 32 million individual data points!)

Dutch school teacher Hanny van Arkel noticed a curious blue cloud next to one of the galaxies shown below which is now known as Hanny's Voorwerp (voorwerp is Dutch for "object").
Now a word about the image...this image was made by combining pictures taken through three different filters: a green, a red and an infrared. So green is used for the blue channel, red is used for the green channel, and infrared is used for the red channel. The practical upshot of this is that something that appears almost entirely blue in this image is, in reality green (the SDSS does not use a blue filter but does use a near ultraviolet filter so you could make a picture with ultraviolet, green and red where this cloud would look green...they did that in the AOL story on the topic).

So what is this? Is it in our galaxy and just happens to lie in the same part of the sky or is it physically associated with the galaxy? Well, the took a spectrum of it and found that it lies at the same distance, so it is associated with the galaxy. The spectrum is shown below.
See that REALLY tall peak slightly to the right of 5000 Angstroms (an Angstrom is a billionth of a meter). That line tells us there is doubly ionized oxygen present and guess what color that is? You got it, green! (I know it says OIII, but OI is neutral oxygen and OII is singly ionized oxygen so OIII is doubly ionized oxygen.)

So, here's what we think is going on. The galaxy appears normal right now. However, it has a massive black hole at its center. When a massive black hole eats a lot of matter, it gives off a lot of energy. As gas spirals toward the black hole, it heats up to millions of degrees and becomes blindingly bright. We think this galaxy's black hole was eating up until about 100,000 years ago and then finished its meal so the galaxy looks normal now.

However, the galaxy used to be much brighter. We are now seeing that energy emitted when the black hole was eating interacting with that gas and causing it to glow...we are seeing a light echo! Since the black hole is no longer eating, we can watch that light echo fade over the next 100,000 years or so and that gas cloud will fade from view!

We have never really seen an interaction like this before and astronomers are very interested in it. So interested that it is being observed by lots of major observatories and satellites including Hubble.

The really neat thing is that this was discovered by an amateur. The SDSS makes all of its data available to the public on the Skyserver web site. You can peruse images of hundreds of millions of galaxies and stars. And sign up for Galaxy Zoo...they are about to star the second phase with fresh objects and new tools to help amateurs make more such discoveries. Who knows, we could end up with kk's Conudrum, Huck's Hullabaloo, Stus Stuff, or AA's Abomination!