NASA / STScI

The galaxies NGC 2207 (left) and IC 2163 are entangled in a picture from the Hubble Space Telescope. Such mergers are the focus of Galaxy Zoo's latest project.

Galaxy Zoo's latest online research project is a "cosmic slot machine" that asks users to match up simulations of galactic smash-ups with pictures of the real things. The payoff? That comes in the form of citizen science.

Over the past two years, Galaxy Zoo has enlisted 250,000 Internet users to classify hundreds of thousands of galaxies from the Sloan Digital Sky Survey - an effort that so far has resulted in 15 scientific papers, either submitted or published.

The latest venture, spearheaded by scientists from Oxford University and George Mason University, kicks it up a notch.

"This doesn't replace Galaxy Zoo," Oxford physicist Chris Lintott told me today. "This is an addition. ... It's a classic scientific question: You solve one thing, and you immediately get 600 other questions."

The data sifted through Galaxy Zoo already confirmed and expanded upon what was known about galactic mergers: that they are more common in denser environments, that a few percent of all galaxies in the universe are clashing together even as we speak, and that the rate of star formation in merging galaxies is about twice what it is in solo galaxies.

Now astronomers are hoping Galaxy Zoo can help them figure out the dynamics behind galactic mergers.

"It's like looking at a car crash," Lintott said. "We want to know the answers to two basic questions: What caused it, and what will the final outcome be?"

For example, how common is it for two spiral galaxies to merge with each other and form an elliptical galaxy? Under what conditions do they coalesce into a bigger spiral instead? How do clashing galaxies develop the monster tails occasionally spotted by the Hubble Space Telescope?

To answer such questions, the new program will enlist Internet users to size up pictures from its database of 3,000 galaxy smash-ups. Most of the images were identified as mergers by Galaxy Zoo's minions, and some Hubble imagery has been thrown in to sweeten the pot.

"Visitors to the Galaxy Zoo Mergers site use what's rather like a giant slot machine, with a real image of a galactic merger in the center and eight randomly selected simulated merger images filling the other eight 'slots' around it," Lintott explained in today's announcement of the project. "By randomly cycling through the millions of simulated possibilities and selecting only the very best matches, they are helping to build up a profile of what kinds of factors are necessary to create the galaxies we see in the universe around us - and, hopefully, having fun, too."

As users become familiar with the site, they can make their own tweaks in the simulations to produce better matches for the pictures - by adding or subtracting stars, for example, or flipping the orientation of the galaxies.

"Once you've done this for a while, you get a feeling of what you need to change," Lintott told me.

George Mason University astronomer John Wallin emphasized that you don't have to be an expert in astronomy, or even a veteran of Galaxy Zoo, to participate. "In fact, our evidence shows that not being an expert actually makes you better at this sort of task," he said.

Galaxy Zoo enlists humans because our eyes and brains are much better than even the most sophisticated machines when it comes to finding similarities between the real and the simulated mergers. Once the most accurate computer simulations are identified, that software can be run forward and backward to reconstruct the galaxies' past and forecast their future.

"These collisions take millions of years to unfold, and so all we get from the universe is a single snapshot of each one," Anthony Holincheck, a graduate student at George Mason University, said in today's announcement. "By producing simulations, we will be able to watch each cosmic car crash unfold on the computer."

The Java-based program actually runs the mini-simulations on each user's computer. Lintott said Holincheck came up with the code by adapting Wallin's original Fortran simulation program. "It's a nice merger of Galaxy Zoo's involvement of people with a SETI @ Home-style application of distributed computing," Lintott said.

Lintott acknowledged that sifting through galactic mergers can pose more of a challenge than doing Galaxy Zoo's relatively simple classification tasks. Depending on your standards, you may have to click through hundreds of galaxies to come up with a suitable match. That's part of the experiment, Lintott said.

"We want to show that there are more complicated tasks that people are happy to share doing," he said.

Eventually, the effort is expected to produce new insights into the widescale distribution of different types of galaxies, the dynamics of galactic mergers, and case studies worthy of more detailed follow-ups. Galaxy Zoo participants have been acknowledged in the papers they've sparked, and that will likely be the case for future research as well.

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