Identifying galaxies: everyman's task

The Galactic Zoo is open. And by all accounts, it's doing a land-office business.

Astronomers in Britain and the United States are enlisting people from around the world to help them sort through images of 1 million galaxies from the Sloan Digital Sky Survey, the most ambitious effort to date to map galaxies and quasars in the night sky.

The team's goal is simple: to group these enormous collections of planets, stars, dust, and gas by their shapes – elliptical blobs, stunning pinwheel-like spirals, and an odd assortment of other forms.

As simple as the task sounds, it's far too labor intensive for any individual astronomer, or even large team of astronomers, to tackle in a reasonable amount of time. Yet the payback for science could be huge, the researchers say. The information will help shed light on questions about how galaxies form and evolve. It could help test a recent challenge to a basic assumption about how the universe works. And the information could eventually be used to develop software that would allow computers to efficiently sort through even larger collections of galaxies from more-extensive sky surveys.

The project, dubbed Galaxy Zoo, certainly appeals to amateur astronomers, the project's scientists say. But it's open to anyone with a curiosity about the cosmos and an eye for sometimes-subtle detail. Art majors are welcome. The only nonhuman tools required: a computer and an Internet connection.

Like most scientists, astronomers typically tend to show people what they do, explains Chris Lintott, a junior research fellow at Britain's Oxford University and one of the organizers of the effort. "In this case, we really need them. We can't do this without the public."

Research groups with other aims have said much the same. They've used the internet to gather large ensembles of people to crunch numbers on home computers for a range of aims: finding radio signals from extraterrestrials, unraveling the secrets of proteins, modeling climate change – even solving large math problems and running particle-physics simulations. But these projects only love the public for its hardware. Once the programs are set up, the software can run with no additional intervention from the home-computer owner.

Harnessing the human eye

Galaxy Zoo's main tool is the human eye and human judgment. No computer can match those when it comes to the kind of pattern recognition this project requires, Dr. Lintott says.

The project stemmed from a Oxford graduate student's desperation. The student, Kevin Schawinski, was trying to perform this type of analysis on 50,000 galaxies in the Sloan collection en route to his PhD. But another conclusion emerged from that work: "After 50,000 galaxies, you never want to see one again," Lintott says. Yet both scientists also saw enormous value in completing the analysis for the entire Sloan sample.

And while the team initially thought participants would post a new result once every one or two seconds,"We've gotten 20 times that," says Alex Szalay, a professor of physics and astronomy at The Johns Hopkins University and an architect of the Sloan Digital Sky Survey's database.

They drew their inspiration for Galaxy Zoo from NASA's Stardust mission, which captured and returned samples of interstellar dust to an eager horde of scientists back on Earth. It also captured other bits of cosmic flotsam and jetsam in a special dust-gathering gel. Stardust scientists asked home-computer users to look at online images of the gel to help identify the tracks that signaled dust.

"Looking at galaxies is much more interesting than looking at dust!" Lintott quips.

A clue for a 'universal' riddle

Researchers are looking at immediate uses for the data people provide. For Lintott, elliptical galaxies and how stars form in them are of keen interest. Theories of galaxy formation suggest that elliptical galaxies should form late in the universe's history; "they should just be forming now," he says. But some of the oldest stars in the universe are found in these galaxies. One approach is to look at elliptical galaxies nearby that are forming stars to see if they hold clues to this paradox. This effort to classify galaxies will help him select ones for study, Lintott adds.

The project was formally announced last Wednesday. Within the first 60 hours, 40,000 people signed up. Web hits vaulted to 6.5 million. The project's initial array of Internet servers ground to a halt under the load. So far, some 650,000 galaxies have received an initial classification. And while 40,000-plus pairs of eyes seem like plenty to do the job, more are needed. "We need to get 10 to 20 classifications per galaxy," Dr. Szalay says. This would allow the scientists to more readily determine a galaxy's most likely shape. "We still have a lot of galaxies no one has looked at."

The project, which also includes researchers from the University of Portsmouth in England, is drawing positive reviews from participants. Writes one member of a British government agency in an e-mail to the project team: "Just had a go at my first few galaxies. A great idea, and genuinely humbling to think that you're looking at something rarely or never seen before."