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The Science behind the Site

For more than 15 years, we've asked volunteers to help us explore galaxies near and far, sampling a fraction of the roughly one hundred billion that are scattered throughout the observable Universe. Each one of the systems, containing billions of stars, has had a unique life, interacting with its surroundings and with other galaxies in many different ways; the aim of the Galaxy Zoo team is to try and understand these processes, and to work out what galaxies can tell us about the past, present and future of the Universe as a whole.

Our strategy is based on the remarkable fact that you can tell a lot about a galaxy just from its shape. Find a system with spiral arms, for example, and normally - but critically not always - you'll know that you're looking at a rotating disk of stars, dust and gas with plenty of fuel for future star formation. Find one of the big balls of stars we call ellipticals, however, and you're probably looking at a more mature system, one which long ago finished forming stars. The galaxies' histories are also revealed; that elliptical is likely to be the product of a head-on collision between two smaller galaxies, and smaller features such as warped disks, large bulges or long streams of stars bear testament to the complexity of these galaxies' lives.

Internal changes - what astronomers sometimes call 'secular' processes - can make a difference too. Each large galaxy has at its heart a massive black hole, and there is growing evidence that as matter falls towards these central black holes, it can have a dramatic effect on its surroundings; the matter is heated to enormous temperatures, glowing brightly in high-energy parts of the electromagnetic spectrum such as the x-ray. There might also be powerful jets of material launched from close to the black hole (though not, of course, from the black hole itself) at close to the speed of light. The combination of these jets and the effect of the radiation sometimes heats or expels gas from the galaxy, preventing - for a time, at least - further star formation.

A galaxy's surroundings matter too. At the centre of the Virgo cluster, our nearest large group of galaxies, mergers between systems are rare - held by the cluster's powerful gravitational grip, galaxies are moving too fast for more than brief encounters. In the emptiest parts of space, the density of galaxies is just too low for mergers to play a significant role, and so it's only on the outskirts of clusters or in small groups like our own Local Group that mergers currently play a significant part. It should come as no surprise, then, that we find different types of galaxies in different places, and this too must be taken into account.

Disentangling these effects, and many more, requires the largest possible samples of classified galaxies. It's not uncommon for us to need, for example, a large sample of red, barred, spiral galaxies that reside on the edges of clusters, and if we don't have a large sample to begin with there will be none left when we've narrowed the search. Modern surveys provide enough images - hundreds of thousands upon hundreds of thousands of them - but we still need people to sort them out by shape. That's where Galaxy Zoo comes in.

You can read much more about the scientific adventures Galaxy Zoo has already had on our blog, or in the papers we've written which are listed at Zooniverse.org/publications.

Live on the Site Now

Galaxy Zoo: JWST

Many different teams of scientists are using NASA’s latest space telescope, JWST to image galaxies so far away that they are back at the earliest time galaxies appear in the Universe.

Tuesday 29th April 2025: we are thrilled to announce the launch of the Galaxy Zoo JWST project, with hundreds of thousands of galaxy images from the COSMOS-Web survey taken with the James Webb Space Telescope (JWST). COSMOS-Web is the largest of the extragalactic surveys approved on JWST. We’ll continue to work in the team to add more images from other JWST surveys, and try to meet our goal to work with you to classify all of the distant galaxies imaged by JWST in a consistent way

For this new phase of Galaxy Zoo we’re joining the NASA Citizen Science family (everyone is welcome to classify; no citizenship needed).

This research (i.e. the team work to select and generate the images we want you to classify from these surveys) was supported by the International Space Science Institute (ISSI) in Bern, through ISSI International Team project #23-584 (Development of Galaxy Zoo JWST).

Previous Images

For a summary of all the many different sets of images Galaxy Zoo has analysed since launch in July 2007, please see the Results Tab.