Citizen science: exploring the Milky Way Project

We caught up with Dr Sarah Kendrew and Dr Robert Simpson at the National Astronomy Meeting to talk about the Milky Way Project.

One of the regions studied by the Milky Way Project. Credit: NASA/JPL-Caltech/Univ. of Wisconsin

We caught up with Dr Sarah Kendrew and Dr Robert Simpson at the National Astronomy Meeting to talk about the Milky Way Project, which gets members of the public identifying ‘bubbles’ within infrared images of our galaxy.

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The project works by asking users to draw around features in the images that they think look like bubbles.

The aim is to build a huge catalogue of bubbles that can be studied to see what it can reveal about star formation and the Galaxy itself.

How did the Milky Way Project come about?

RS: I started working at the Zooniverse and have a background in star formation.

We thought we should really do a star formation [citizen science] project and realized that the data we should study was from the Spitzer Infrared Space Telescope.

We realized that the existing surveys that had been done had often been done by eye, by people.

So we said if you could do that with four people we’re sure we could do it with 40,000.

SK: We first actually tried to find all different kinds of objects.

It took us a while to figure out that bubbles were the things that we were really good at identifying.

What are the bubbles?

SK: The majority of the ones that we’re finding are formed around massive stars or clusters of massive stars.

They form when the star starts emitting ionizing radiation.

It sweeps away the dense material that it formed from and blows a shell out around itself that is filled with ionized gas.

But there are all kinds of other objects that can create these bubbles: supernovae can create shells when they explode, planetary nebulae, other types of massive stars that loose a lot of mass as they evolve, and sometimes they are just holes in the interstellar medium that form from random motions of the material.

Some of the bubbles identified by users of the Milky Way Project (centre) and part of the final catalogue (right). Credit: NASA/JPL-Caltech/R. Simpson (Oxford University)
Some of the bubbles identified by users of the Milky Way Project (centre) and part of the final catalogue (right). Credit: NASA/JPL-Caltech/R. Simpson (Oxford University)

How many users does the Milky Way Project have?

RS: In the studies that we have put out so far 35,000 people took part and contributed.

The actual number of users on the website today is up to about 40,000.

How many bubbles have you found?

SK: It’s a difficult question to answer.

In total we had nearly two million drawings of interesting things.

Then of course we have to apply some quality metrics.

You want a minimum number of drawings before you say you’ve definitely identified a bubble and its location.

RS: We had half a million drawings of bubbles that we condensed down to form a catalogue of about 15,000 bubbles.

Then we applied quality controls to end up with 5,106 bubbles.

How good are the citizen scientists at identifying bubbles?

RS: We found that we recovered approximately 90% of the bubbles listed in existing catalogues.

What do the bubbles tell us?

RS: They tell us where there’s star formation going on in the Galaxy, we think.

So we’re essentially getting our users to draw a crowdsourced map of where there is star formation activity in the Milky Way.

Our initial study was all about bubbles, but our users have also been identifying star clusters, dark nebulae and all those other things that also contribute to an atlas of star formation.

SK: We studied the Milky Way Project bubble catalogue alongside another catalogue of massive young stellar objects that were identified by another space mission.

We found that around the apparent edges of the largest bubbles we see more massive young stars in the process of forming than you would expect from just a random distribution.

This could be indicative of a process called ‘triggering’.

This is where a massive young star causes new pockets of gas to collapse and form new stars as it compresses all the material around the edges of a bubble

What’s next for the Milky Way Project?

RS: We’ve just switched to a new mode of operation actually.

We used to show people random chunks of the galactic plane and ask them to draw what they see.

Now we’ve switched it round.

We decided that we need really good measurements of the bubbles our users have found.

So they are now combing through the catalogue they created.

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By asking people to go through the images in greater detail – with the smaller bubbles now blown up bigger – we’re going to get better parameters for all their physical sizes.