Galaxy Zoo

Galaxy Zoo is a crowdsourced astronomy project which invites people to assist in the morphological classification of large numbers of galaxies. It is an example of citizen science as it enlists the help of members of the public to help in scientific research.

There have been 15 versions as of July 2017. Galaxy Zoo is part of the Zooniverse, a group of citizen science projects. An outcome of the project is to better determine the different aspects of objects and to separate them into classifications.

Origins

A key factor leading to the creation of the project was the problem of what has been referred to as data deluge, where research produces vast sets of information to the extent that research teams are not able to analyse and process much of it. Kevin Schawinski, previously an astrophysicist at Oxford University and co-founder of Galaxy Zoo, described the problem that led to Galaxy Zoo's creation when he was set the task of classifying the morphology of more than 900,000 galaxies by eye that had been imaged by the Sloan Digital Sky Survey at the Apache Point Observatory in New Mexico, USA. "I classified 50,000 galaxies myself in a week, it was mind-numbing." Chris Lintott, a co-founder of the project and a professor of astrophysics at the University of Oxford, stated: "In many parts of science, we're not constrained by what data we can get, we're constrained by what we can do with the data we have. Citizen science is a very powerful way of solving that problem."

The Galaxy Zoo concept was inspired by others such as Stardust@home, where the public was asked by NASA to search images obtained from a mission to a comet for interstellar dust impacts. Unlike earlier internet-based citizen science projects such as SETI@home, which used spare computer processing power to analyse data (also known as distributed or volunteer computing), Stardust@home involved the active participation of human volunteers to complete the research task. In August 2014, the Stardust team reported the discovery of first potential interstellar space particles after citizen scientists had looked through more than a million images.

In 2007, when Galaxy Zoo first started, the science team hoped that 20–30,000 people would take part in classifying the 900,000 galaxies that made up the sample. It had been estimated that a perfect graduate student working 24 hours a day 7 days a week would take 3–5 years to classify all the galaxies in the sample once. However, in the first Galaxy Zoo, more than 40 million classifications were made in approximately 175 days by more than 100,000 volunteers, providing an average of 38 classifications per galaxy.

Chris Lintott commented that: "One advantage is that you get to see parts of space that have never been seen before. These images were taken by a robotic telescope and processed automatically, so the odds are that when you log on, that first galaxy you see will be one that no human has seen before." This was confirmed by Kevin Schawinski: "Most of these galaxies have been photographed by a robotic telescope, and then processed by computer. So this is the first time they will have been seen by human eyes.".

Volunteers

Galaxy Zoo recruited volunteers to help with the largest galaxy census ever carried out. Opening the project to the general public saved the professional astronomers the task of studying all the galaxies themselves, resulting in classification of a large number of galaxies undertaken in a shorter time than what smaller research teams would be able to do, classifying 900,000 galaxies in months rather than years if done by smaller research teams. Computer programs had been unable to reliably classify galaxies: several groups had attempted to develop image-analysis programs. Kevin Schawinski stated: "The human brain is actually much better than a computer at these pattern recognition tasks." However, volunteers astonished the project's organizers by classifying the entire catalog years ahead of schedule. An online forum was later set up two weeks after the initial start, partially due to a large volume of emails being sent around, to the point that it was troublesome for those receiving them to process and respond to them. This led volunteers to point out anomalies that on closer inspection have turned out to be new astronomical objects such as 'Hanny's Voorwerp' and ' the Green Pea galaxies'. “I’m incredibly impressed by what they’ve managed to achieve,” says University of Oxford astronomer Roger Davies, former president of the Royal Astronomical Society.“They’ve made it possible to do things with a huge survey.”

The Galaxy Zoo forum became a hotbed for the discussion of the SDSS images and more general science questions. Its 'global moderator', volunteer communuity manager and UK astronomy enthusiast Alice Sheppard, said of it: "I don't quite know what it is, but Galaxy Zoo does something to people. The contributions, both creative and academic, that people have made to the forum are as stunning as the sight of any spiral, and never fail to move me." Author Michael Nielsen wrote in his book Reinventing Discovery: "But Galaxy Zoo can go beyond computers, because it can also apply human intelligence in the analysis, the kind of intelligence that recognizes that Hanny's Voorwerp or a Pea galaxy is out of the ordinary, and deserves further investigation. Galaxy Zoo is thus a hybrid, able to do deep analyses of large data sets that are impossible in any other way." A community feeling was also created. Roger Davies stated: "The community of Galaxy Zoo gives them the opportunity to participate that they’re looking for.” This community became known as the 'Zooites'. Aida Berges, a homemaker living in Puerto Rico who has classified hundreds of thousands of galaxies, stated: "Every galaxy has a story to tell. They are beautiful, mysterious, and show how amazing our universe is. It was love at first sight when I started in Galaxy Zoo ... It is a magical place, and it feels like coming home at last." The Galaxy Zoo Forum became a read-only archive in July 2014. After seven years online and over 650,000 posts, it continues to generate science.

As of July 2017, 60 scientific papers have been published as a direct result of Galaxy Zoo and hundreds of thousands of volunteers. In previous studies though, it was found that data produced by volunteers was more likely to contain bias or mistakes. However Chris Lintott says that crowdsourced results are reliable, as proven by the fact that they are being used and published in peer-reviewed science papers. Indeed, other scientists have questioned crowdsourcing and crowdsourced studies. Steven Bamford, a Galaxy Zoo research scientist, stated: "As a professional researcher you take pride in the work that you do. And the idea that anybody off the street could come and do something better sounds threatening but also implausible." David Anderson, the founder of BOINC, stated: or many sceptical scientists"There's this idea that they're giving up control somehow, and that their importance would be diminished". The continuing goodwill of citizen scientists is also questioned. Chris Lintott stated: "Rather than letting anyone pitch for volunteers, we'd like to be a place where people can come and expect a certain level of commitment".

A conference was held between 10–12 July 2017 at St. Catherine's College, Oxford, to recognise the tenth anniversary of the start of Galaxy Zoo in July 2007. Co-founder Chris Lintott stated: "What started as a small project has been completely transformed by the enthusiasm and efforts of the volunteers... It has had a real impact on our understanding of galaxy evolution." 125 million galaxy classifications resulting in 60 peer reviewed academic papers from at least 15 different projects have been made since July 2007. Discoveries include: Hanny's Voorwerp, Green pea galaxies and more recently objects known as 'Yellow Balls'. On the conference Twitter feed, #GZ10, it states that 10 of the 60 papers have over 100 citations ithin the Astrophysics Data System">Astrophysics_Data_System.html" ;"title="ithin the Astrophysics Data System">ithin the Astrophysics Data Systemin 10 years. Karen Masters, an astrophysicist at Portsmouth University and project scientist for GZ stated: "We're genuinely asking for help with something we cannot do ourselves and the results have made a big contribution to the field." As a result of GZ's success, the citizen science web portal Zooniverse was started, which has since hosted a 100 projects.

Retired projects

Galaxy Zoo 1

The original Galaxy Zoo consisted 100,000 galaxies imaged by the Sloan Digital Sky Survey. With so many galaxies, it had been assumed that it would take years for visitors to the site to work through them all, but within 24 hours of launch, the website was receiving almost 70,000 classifications an hour. In the end, more than 50 million classifications were received by the project during its first year, contributed by more than 150,000 people. This was started in July 2007 and retired in 2009.

Galaxy Zoo 2

This consisted of some 250,000 of the brightest galaxies from the Sloan Digital Sky Survey. Galaxy Zoo 2 allowed for a much more detailed classification, by shape and by the intensity or dimness of the galactic core, and with a special section for oddities like mergers or ring galaxies. The sample also contained fewer optical oddities. The project closed with some 60 million classifications. Started and retired .

Galaxy Zoo mergers

This studied the role of interacting galaxies. Interacting galaxies are galaxies that exhibit a gravitational influence on one another. This influence is exhibited over the course of millions or even billions of years as two or more galaxies pass nearby one another. The near passage of two massive structures can cause the galaxies to be distorted and possibly merge. The Galaxy Zoo Mergers aimed to provide a set of tools that allowed users to randomly sample various sets of simulation parameters in rapid succession by showing 8 simulation outputs at a time. This started in November 2009 and was retired in June 2012.

Galaxy Zoo supernovae

Galaxy Zoo used images partner from the Palomar Transient Factory to find Supernovae. The task in this Galaxy Zoo project was to help catch exploding stars – supernovae. Data for the site was provided by an automatic survey in California at the Palomar Observatory. Astronomers followed up on the best candidates at telescopes around the world. This started in August 2009 and was retired in August 2012.

Galaxy Zoo Hubble

The site's third incarnation, Galaxy Zoo Hubble drew from surveys conducted by the Hubble Space Telescope to view earlier epochs of galaxy formation. In these surveys, which involve many days of dedicated observing time, we can see light from galaxies which has taken billions of years to reach us. The idea behind Galaxy Zoo Hubble was to be able to compare galaxies then to galaxies now, giving us a clear understanding of what factors influence their growth, whether through mergers, active black holes or simply star formation. This started in April 2010 and was retired in September 2012.

In October 2016, a study titled: "Galaxy Zoo: Morphological Classifications for 120,000 Galaxies in HST Legacy Imaging" was accepted for publication by the journal Monthly Notices of the Royal Astronomical Society. The abstract begins: "We present the data release paper for the Galaxy Zoo: Hubble project. This is the third phase in a large effort to measure reliable, detailed morphologies of galaxies by using crowdsourced visual classifications of colour composite images. Images in Galaxy Zoo Hubble were selected from various publicly-released Hubble Space Telescope Legacy programs conducted with the Advanced Camera for Surveys, with filters that probe the rest- frame optical emission from galaxies out to z ≈1."

Galaxy Zoo 4

The present Galaxy Zoo (4) combines new imaging from the Sloan Digital Sky Survey with the most distant images yet from the Hubble Space Telescope CANDELS survey. The CANDELS survey makes use of the new Wide Field Camera 3 to take ultra-deep images of the universe. The project also includes images taken with the United Kingdom Infrared Telescope in Hawaii, for the recently completed UKIDSS project. UKIDSS is the largest, deepest survey of the sky at infrared wavelengths. Kevin Schawinski explained that: "The two sources of data work together perfectly: the new images from Sloan give us our most detailed view of the local universe, while the CANDELS survey from the Hubble telescope allows us to look deeper into the universe’s past than ever before."

In October 2016, a paper was accepted for publishing in MNRAS titled: "Galaxy Zoo: Quantitative Visual Morphological Classifications for 48,000 galaxies from CANDELS". Quoting: "We present quantified visual morphologies of approximately 48,000 galaxies observed in three Hubble Space Telescope legacy fields by the Cosmic And Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and classified by participants in the Galaxy Zoo project. 90% of galaxies have z < 3 and are observed in rest-frame optical wavelengths by CANDELS. Each galaxy received an average of 40 independent classifications, which we combine into detailed morphological information on galaxy features such as clumpiness, bar instabilities, spiral structure, and merger and tidal signatures."

Active projects

Radio Galaxy Zoo

On 17 December 2013, Galaxy Zoo opened a project called Radio Galaxy Zoo. It uses observations from the Australia Telescope Large Area Survey in Radio, and compares them to the Spitzer Space Telescope's infrared data. There are about 6000 images to look through. The CSIRO press release states that Radio Galaxy Zoo is a new citizen science project that lets anyone become a cosmic explorer. It continues that by matching galaxy images with radio images from CSIRO's Australia Telescope, a participant can work out if a galaxy has a supermassive black hole.

Other ongoing projects

Another project that uses data from volunteer classifications is Galaxy Zoo Quench, which studies the interactions between galaxies and the effect it has on starbursts (among others). This has yet to be completed.

Complete list of projects

As of July 2017, the full list of Galaxy Zoo projects (15) is: Galaxy Zoo 1, Galaxy Zoo 2, Galaxy Zoo Mergers, Galaxy Zoo Supernovae, Galaxy Zoo Hubble, Galaxy Zoo CANDELS, Radio Galaxy Zoo, Galaxy Zoo Quench, Galaxy Zoo DECALS 1, Galaxy Zoo DECALS2 + SDSS, Illustris, UKIDSS, Galaxy Zoo Bar Lengths and two more.

Related

In June 2019, citizen scientists through Galaxy Zoo reported that the usual Hubble classification, particularly concerning spiral galaxies