This is Dr. Breanna Binder, a postdoctoral researcher at Cal Poly Pomona who joined the Milky Way Project team over the last year. I’m hoping to use the classification powers of all you awesome citizen scientists to find… computer-generated bubbles. Read on to find out why!
Thanks to the hard work and dedication of all you volunteers, the Milky Way Project has produced catalogs of thousands of bubbles. These bubbles come in a variety of shapes and sizes and are located in many different types of environments – from the hectic downtown of the Galactic center to the relatively sparse suburbs of the outer disk. With this catalog in hand, we naturally want to start using it to ask scientific questions: What causes some bubbles to be circular in shape, but other oval? Do we find small bubbles in certain environments but not others? And when we do find interesting differences or correlations in our catalog, we of course have to ask: Why?
Before we can answer these questions, there’s another we need to consider first: How do we know if there are bubbles missing from our catalog? It seems reasonable that the smaller or fainter a bubble appears in an image, the easier it will be for our volunteers to miss. Similarly, a bubble in a very dense environment (like the left-hand picture below) might get lost in the crowd of its brighter or larger neighbors, even though that same bubble would be easily identified if it were isolated from other interesting star formation features (like in the right-hand image below).
If we want to interpret the trends observed in our bubble catalog, we need to understand the completeness of our catalog. Let’s take the sizes of bubbles as an example: big bubbles are easier to identify and measure than small bubbles. So, we might expect that our volunteers were able to identify all of the bubbles bigger than a certain size (100% completeness) but were only able to find a third of bubbles smaller than some other size (33% completeness). Not only would we like to be able to estimate the total number of bubbles we’re missing, but we want to know how many we’re missing as a function of some interesting parameter (in this case, size).
How can we possibly do this? After all, we’re only able to identify… well, what we’re able to identify! So how can we measure the completeness of our bubble catalog?
The solution comes from computer simulations. We’ve partnered up with Dr. Christine Koepferl at the University of St. Andrews, who creates realistic, computer-generated synthetic bubbles that can be viewed at multiple distances and from many different viewing angles. These synthetic bubbles are so realistic-looking that even Milky Way Project technical lead Tharindu Jayasinghe and bow shock guru Don Dixon couldn’t tell them apart from the real thing!
I’ve taken Dr. Koepferl’s synthetic bubbles and added them to the Milky Way Project images. Since these are computer-generated images, I can specify exactly how many bubbles to add, where to place them in the images, how big they should appear, whether or not the bubble should be rotated or viewed from a different angle, etc. These modified observations – some of which contain a synthetic bubble – are then loaded back into the Milky Way Project.
This is the key to measuring the completeness of a survey! We know everything about the true distribution of the synthetic bubbles, so we can see how accurately our citizen scientist volunteers are able to find and measure them. If our volunteers find all the synthetic bubbles larger than a certain size, then we can be pretty confident they found all the real bubbles larger than that, too. However, if they are only able to pick out a third of small bubbles, then it’s likely that the small bubbles in our catalog only represent a third of the total number of small bubbles out there.
This information is really important for estimating the total number of bubbles in the Milky Way, and could have other very interesting implications for the distribution of bubbles in our Galaxy. This sort of completeness study was not conducted in the earlier versions of the Milky Way Project, and is not normally done in other citizen science initiatives either. We hope that you will continue to search for bubbles – both real and computer-generated – to help the Milky Way Project once again push the boundaries of what citizen science can accomplish!