THE task of peering into the cosmos and discovering strange new galaxies sounds like a job for astronomers armed with big and very expensive telescopes. But almost a year ago that all changed when a group of stargazers decided to ask the public to help in a project to explore the northern sky.

The Sloan Digital Sky Survey had been looking in this part of space for 16 years, producing so much information that astronomers assumed they would never get through it. So the public was let loose, to help sort what they had found. The scheme is called the Galaxy Zoo project.

It was so popular, says Alex Szalay, an astronomer at John Hopkins University, Maryland, that the computer servers on which the project ran “literally overheated and blew a fuse”. More important, within a month of the opening, Hanny van Arkel, a physics teacher from the Netherlands, posted a message on the zoo's forum about some strange blue stuff she had spotted and asked what it might be.

By January the zoo's professional keepers had started to pay attention to what the teacher had called a voorwerp, the Dutch word for object. Now it is becoming famous. William Keel, an astronomer at the University of Alabama, took another picture of the voorwerp and suggested that the human eye would probably see it as green, rather than blue as in the original picture. It also has a giant hole at its centre.

What this object might be was a complete mystery at first. It was initially thought to be a distant galaxy, says Chris Lintott, an Oxford University astronomer involved in the project. But after further study astronomers realised that there were no stars in it, and so it must be a cloud of gas. But why the gas was so hot (about 15,000ºC) was a mystery, because there seemed to be no stars to heat it up.

Now, in a posting on the Galaxy Zoo blog, Dr Keel and Dr Lintott suggest that the galaxy right next door to the voorwerp used to be a quasar (a very bright active galactic nucleus) that has since eaten up all its fuel. This quasar lit up the nearby gas, and although the quasar has since gone out, the light from it is still travelling to the object. The blob, says Dr Lintott, sees the galaxy as it was 40,000 years ago. This makes the voorwerp a sort of light echo but on a massive scale. Smaller light echoes have been seen around supernovae. As for the giant hole, Dr Lintott has “no sensible explanation” for that at the moment and needs to wait for more telescope time.

The weird blob could become immortalised as Hanny's Voorwerp, the name given to the object in a paper Dr Lintott and his colleagues are submitting to the Monthly Notices of the Royal Astronomical Society. And towards the end of the year, if the mission to service the Hubble telescope goes as planned, a high-quality image of the voorwerp could emerge.

Data direct

Earlier projects in distributed computing, such as SETI@home, which searched for extraterrestrial life, have used the power of millions of home computers. But more recently, scientists have begun to realise that distributed human brain power itself can be a useful commodity, as in working out the shape of proteins. Dr Szalay says that the voorwerp episode has shown how immensely valuable the public can be.

When the data were put online Dr Szalay thought it was only a matter of time before someone made a big discovery. “It just happened much faster than we thought.” In the past year 40m classifications of galaxies have been submitted on 1m galactic objects in the Galaxy Zoo. Dr Lintott says that the project has proved that the public en masse is as good as professional astronomers at classifying galaxies.

The next step is to ask people to do more complicated things, such as keeping an eye out for weird objects, which is bound to appeal to armchair astronomers. Hanny's object had been there for decades, unnoticed in the astronomical archives. The idea now is for the public to explore strange new galaxies; to seek out new voorwerps and to boldly go where no amateur has gone before.