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Galaxy Zoo 1 and 2 have already produced lots of brand new science — have a look at 'The Story So Far' section for details of what we've done with all the clicks on the websites. However, they only give us a glimpse of the nearby Universe. With Galaxy Zoo: Hubble we can look further back than ever before, and begin to understand how the Universe has changed over time.
Just as with the original incarnations of Galaxy Zoo, the aim of the project is to collect information on the shape of the galaxies. This one fact turns out to be a guide to many other facts about a galaxy. Find a spiral galaxy and normally - but crucially not always — you'll know that it's a rotating disk which has plenty of fuel for its ongoing star formation. A typical elliptical, on the other hand, has older stars and will have long since finished forming stars.
These rules don't always hold, and finding the exceptions has been one of the important results from Galaxy Zoo to date, but they do illustrate just how important knowing the shape of a galaxy is. With Galaxy Zoo: Hubble, we want to see how the mix of galaxies has changed over time. More stars were forming back then, so does that mean we should expect more spirals? Or does the proportion of blue ellipticals increase as we travel back in time? Only you can tell us.
Another critical question is what happens to the number of merging galaxies. We know that a merger can have a dramatic effect on the galaxies involved; one good way to form an elliptical, for example, is to collide two spirals together. The question is how much of an effect mergers had in producing the mix of galaxies we see today and to determine that we need to know how common they were in the past. Yesterday's mergers may well have produced today's galaxies.
Each of the questions we ask is designed to get more useful information about the galaxies that lurk in the images. The shapes of ellipticals contain information about their past, and many spiral galaxies have bars across their centres, including our own Milky Way galaxy. How these bars formed, how long they exist, and what their connection is to galaxy evolution is also a currently debated topic, and comparing Hubble and Sloan data will help us unravel the answers.
Then there are other questions to ask about a galaxy, such as: What fraction of galaxies have two, three, or more arms? How tightly wound are the spiral arms? Does the galaxy have a 'boxy' or a 'rounded' bulge? How many galaxies are there with 'irregular' morphologies? Answering these questions about every galaxy, one galaxy at a time, is essential if we're going to understand the fine details of galaxy formation.
Those of you who took part in Galaxy Zoo 2 will have noticed that there's a whole new set of questions. Previous studies of galaxy shapes in Hubble data sets have noticed a greater number of irregular galaxies, and so we want to make the first systematic study of these intriguing objects.
We want to know the answer to all these questions, and more. The primary goal of Galaxy Zoo is to construct a database of detailed shape information for almost all the galaxies the Hubble Space Telescope has ever seen. Such a database will have substantial legacy value for the international astronomy community. In short, we hope to find out everything there is to know about the appearance of galaxies!
If you've read the 'How to Take Part' page then you know that we're also asking you to keep a look out for some rarer objects.
The sharp-eyed visitors to the Galaxy Zoo are very good at spotting the weird and wonderful — indeed, this is one of the most active areas of the discussion forum. So, we'd like to see if we can help the community be more effective at discovering certain types of rare object. We have several examples in mind for GZ2, based on the kinds of things found by the community so far.
Gravitational lenses are galaxies and groups of galaxies that are so massive that they bend the path of light from more distant objects towards themselves, distorting the shapes of background galaxies into arcs and rings, and even causing multiple copies of the images of galaxies and quasars to appear in symmetrical patterns around them on the sky. These cosmic alignments are quite rare — only about one in a thousand elliptical galaxies is acting as a lens in this way. In some cases it is possible to find them using clever image analysis software, but the most interesting cases are too complex for this. However, humans seem to be very good at recognising the tell-tale signs of gravitational lensing!
Why do we want to know about more instances of gravitational lensing? The separation of the multiple images allows us to weigh the lens galaxy, something that is typically very hard to do in astronomy. Once we have measured the mass of the lens, we then know how strong a lens it is — and how much magnifying power it has. The lensed images appear typically 10-100 times brighter than they would without the lens: we can use gravitational lenses as cosmic telescopes to observe the very distant universe. And as usual, the more telescopes we have the better!
Galaxies can grow in two ways: by forming stars, or by merging together. Our current theories of galaxy formation expect there to be a lot of merging happening, and indeed we do see many examples, but it is very difficult to reliably measure how much merging is really going on. We need big samples, and keen eyes — Sounds like a job for Galaxy Zoo!
One of the most exciting discoveries from the original Galaxy Zoo was something we never expected. Hanny Van Arkel, a Dutch schoolteacher and Galaxy Zoo volunteer, posted an image to the Galaxy Zoo forum and asked 'What's the blue stuff below?' No one knew. The object became known as Hanny's 'Voorwerp' — Dutch for 'object'. The original images from the Sloan Digital Sky Survey couldn't tell us what it was, so we've taken follow-up telescope observations, in the optical, ultra-violet, and radio ranges, as well X-ray measurements from several satellites and exquisite images from the Hubble Space Telescope.
Blog links:
The Voorwerp is shown above but you can read more about it and see additional examples on the Galaxy Zoo blog article: The Mystery Deepens.
The main possibilities opened up from our data involve a brilliant quasar — the powerful fireworks accompanying the growth of a supermassive black hole — shining at the centre of the galaxy seen just above the Voorwerp. However, this quasar has either turned off in the last 100,000 years or so, leaving the gas shining, or it is so thoroughly hidden from our vantage point that not even X-ray telescopes can find its escaping radiation. Either possibility would significantly alter how we think about quasars and their occurrence in the Universe, and we are working hard to tell which possibility is more accurate - as well as following up smaller-scale examples of 'voorwerpjes' found by Zooites.
The Voorwerp is only one of the many interesting and wonderful objects that users found in Galaxy Zoo 1. Teams of astronomers - and of Zooites - are working hard to follow up on these. It's something that is unique to a project like the Zoo. Computers will slowly get better at classifying galaxies, but looking at an image and asking 'what's that odd thing?' remains uniquely human.
