Finished! Looks like this project is out of data at the moment!
16 SEP 25: Thanks for all of your classifications!! We are now looking at the results of the recently completed Classify AND Refine projects. We will post updates soon and plans for the next searches. Space Warps recently migrated onto Zooniverse’s new architecture. For details, see here.
FAQ
Science
Task
Interface
Training
Science
What is gravitational lensing?
Gravitational lensing is the bending of light by gravity. This isn't noticeable on Earth, but we can see its effects when we look at the most massive galaxies in the universe.
What is a gravitational lens system?
A gravitational lens system consists of a massive galaxy (the 'lens'), and an even more distant galaxy (the 'source'). The light from the distant source galaxy is deflected by the lens galaxy as the light travels towards Earth. We call this a gravitational lens system. These systems are very rare, as they require the lens and source galaxies to be close together on the sky. Therefore most of the images you will inspect won't contain a lens, but some definitely will!
What does a typical lens system look like?
A typical lens system consists of a massive lensing galaxy (or group of galaxies) surrounded by multiple arc-like images of a background galaxy. Sometimes the background object is a quasar; a lensed quasar appears like multiple star-like (i.e. compact) objects around the lensing galaxy.
What's the difference between a lens(ing) galaxy and a lensed galaxy?
The lens/lensing galaxy is the foreground massive galaxy which can warp the space and cause light to bend around it. A lensed galaxy is a distant background galaxy from which light rays emerge and get bent or deflected due to the lens galaxy before arriving on earth.
It is a common shorthand to refer to the lensing galaxy as the 'lens' and the lensed galaxy as the 'source'.
Why are most background galaxies blue and most foreground galaxies yellowish red?
The theory of gravitational lensing suggests that there is an optimal distance at which the background source need to be situated for a massive foreground object to produce the gravitational lensing effect.
We find from many imaging surveys that, as we look back in the nearer half of the Universe there are more elliptical galaxies which are not only much more massive than spiral galaxies but are also dominated by older population of stars. These stars emit light closer to wavelengths that appear yellow and hence, the elliptical galaxies appear yellow. Their larger masses also make them more efficient in deflecting light from background galaxies or quasars to produce multiple images.
We also find that there's a rise in the population of spiral (or star-forming) galaxies at a distance when the Universe was one fourth of its current age. Incidentally, this distance happens to be the optimal distance for us to see the strong lensing due to the foreground ellipticals. And, since the spiral galaxies are dominated by young stars which have hot temperatures and emit light in bluer wavelengths, most of the lensed galaxies appear bluish but there can be exceptions.
Why are gravitational lens systems interesting?
Gravitational lenses have numerous applications in astrophysics. Most importantly, they are used for understanding properties of Dark Matter which is very difficult to probe by other methods. Since lens systems also create magnified images of the distant background galaxies, we can get a better understanding of these distant and faint galaxies which would be impossible otherwise. Other interesting applications include measuring the age of the Universe and finding exoplanets!
Why do you need my help to look for gravitational lenses?
How a lens system will look like in the sky depends on several factors relating to properties of the foreground and the background object. Lens systems can be very complex so the process of detection is extremely challenging to automate completely. One of the major problems is contamination from lens-like systems e.g., spiral galaxies, ring galaxies and other artifacts in the images that mimic arc-like features. Human beings are better at processing and filtering objects that have multiple levels of complexities and finding objects that are unique or show unexpected properties. Lens systems fall in this category and we need your help both in discovering newer types of lenses and building better algorithms.
How do I know what's a lens and what isn't?
We have put up some examples of lenses, and lens impostors, in the Field Guide. This can be seen as a widget on the right-hand of the classification page. You can click on the images to read the description. You can also learn by discussing with others on TALK.
Task
What is my main task?
[CLASSIFY] The main task for the classify stage is to inspect the images shown and mark any of the gravitationally lensed features you can spot in the image (See the Science section on the definition of a gravitational lens). Lens systems are rare: most of the images won't contain any gravitational lenses, but a few images will have a lens and in extremely rare cases, there might be more than one lens in an image. So, watch out!
[REFINE] The task for the refine stage is to inspect the top-ranked strong lens candidates from 'classify;, be more discerning and grade them as definite, probable, possible or unlikely lenses.
Should I try and be inclusive, or discerning?
We don't want to miss the rare gravitational lenses: if in doubt, mark them. The Spotter's Guide can help you in deciding which images are more likely to show gravitationally lensed features. In the refine stage, we do ask you to be more discerning but the categories can help reflect your opinion and uncertainty on any given image you are shown.
Why are there multiple panels for the same objects?
We show a range of images for each candidate galaxy, with different contrast/brightness settings optimised to help in the visual identification of the faint lensed features.
What do I do if I see more than one lensed image per lens system?
[Classify] You should place a marker on at least one lensed feature that you see per lens system, for example, arc-like features or compact (circular) objects called quasars. You only need to mark one of the lensed features for your identification to be registered, but you can mark multiple features if you wish.
Will the images have a lens system always at its center?
The images were selected to all contain objects that could be lenses (like massive yellowish elliptical galaxies, or groups of galaxies) - so it's most likely (although not guaranteed) that if a lens is present, it will be in the middle of the field.
Interface
**These apply to the first [Classify'] stage.
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Where should I put the markers?
OR
I marked a simulated lens but was told that I missed it. What's the problem?
We'd like you to mark any lensed features that you see i.e. you can mark one or all of the curved arcs, or multiple compact (circular) quasars. You can choose any one of the four panels for placing the marker and it will be duplicated.
Sometimes the site will tell you that you missed a simulated lens even after marking it. This may be because the marker is not quite on the lensed object, e.g. the marker might have been placed on the lens galaxy at the center instead of the lensed features around. If you are absolutely sure that there is a bug, please report it on TALK along with the image IDs.
Can I delete my markers?
Yes, if you click on one of your markers, a little cross should appear above it. If you click on this cross, the marker is deleted.
When should I use additional tools?
Many lensed images are faint and very close to the bright yellowish lensing galaxies. You can zoom/pan or invert the color scheme to get a detailed and different view of features near the lensing galaxy and be more confident of not missing a faint lens.
I missed a lens! How do I go back?
The last image you saw is in your 'Recents' list, on your Profile. You cannot modify your classification after you have submitted it but you can click on this image to take it to Talk, where you can tag it for other people to see, and discuss it with them.
I found something interesting! What do I do?
The markers are only for lensed features, but you can mark any image as a "favorite", whether you think it has a lens in it or not, using the heart-shaped button. This will appear in your favorites list on your profile page. You can then click on that image to take it to Talk, where you can discuss it with other people or add it your own collection.
Sometimes a vertical/horizontal section of the image looks completely dark. Why is that?
Nothing to worry about. These images are at the edges of the survey region where the telescope did not collect data. Since there's no data, these sections look dark.
I can't see some pages on the website. What internet browser should I use?
We offer support for the most recent and second most recent version of all major browsers.
Training Images
What are simulated lens systems?
Simulated lens systems are computer generated images of gravitational lens systems using standard models for a foreground galaxy (or galaxy group) and a background galaxy (or a quasar). These simulated lenses are then added to the real images of the sky observed with a telescope.
Why are simulated lenses included rather than real lenses?
The Field Guide shows some typical examples of real lenses. Since lens systems have varied properties but they are very rare, we simulate them in large numbers using computer algorithms. We need a large training sample to understand what kind of lenses are being found or missed. Since we don't have a large number of known real lenses, we generate them using computer algorithms.
Can I turn off the training images ?
We have found that without the training images comprising simulated lenses and lens impostors, we started to make mistakes. We don't want to miss any real lenses, so we thought it best to keep showing the training images, just in case! As you do more classifications we will show you fewer training images. Understanding how you perform on the training images is also important for interpreting the real lenses discovered on Space Warps: we need to know if the sample is biased because certain types of lenses are easier/harder to discover.
We also describe in some detail at this blog post and these papers Marshall et al. and More et al.
Can I turn off the feedback messages?
We have found that since gravitational lenses are so rare, without the feedback messages we tend to lose focus and are likely to make mistakes. We don't want to miss the precious lenses, so we thought it best to keep the messages turned on!