The Bubbling Galactic Disk

Some of the most beautiful structures in Spitzer GLIMPSE data are the bubbles. Bubbles are regions of gas, usually found around newly formed stars, often with shells of material surrounding them (the green 8 μm emission above). These appear as rings in the GLIMPSE images and can vary in appearance from strikingly prominent to intriguingly faint. They can be anything from complete circles and ellipses, to fractured, fragmented remains.

As part of Project IX we’re going to ask you to find and measure these bubbles. Researchers can use this information to learn a lot about how these objects form and how they trigger star formation.

Above is an image of RCW 120, the titual “perfect bubble” from a 2009 paper by Deharveng, Zavagno, Schuller, Caplan, Pomarès and De Breuck. This colour-composite image shows Hα emission in blue, 8 μm emission in green and the 24 μm emission of small dust grains in red. The image is approximately 24′ degrees wide.

The green material has been swept up as the region expanded, after the formation of a massive star in the centre. There are about 2000 Solar masses of neutral material here, and this has fragmented into lumps. This is where star formation is occurring. The authors of the study found 138 potential star-forming objects in the ring around RCW 120.

In 2006, a group of astronomers visually inspected the GLIMPSE data for bubbles and catalogued their results in a paper titled ‘The Bubbling Galactic Disk‘. I’m a sucker for a great paper title. The team behind this study has been looking at the GLIMPSE data ever since. As mentioned above, bubbles are important features in the study of star formation. Here’s how they are described in ‘The Bubbling Galactic Disk‘:

The study of bubbles gives information about the stellar winds that produce them and the structure and physical properties of the ambient ISM – interstellar medium – into which they are expanding. Additional physical insights include the hydrodynamics of gas and dust in expanding bubbles, the impact of expanding bubbles on magnetic fields in the diffuse ISM, and mass-loss rates during the evolution of stars.

In 2006 322 bubbles were visually identified by just a handful of people. Since that time two things have changed. Firstly, there is now a lot more data, and therefore more bubbles. Spitzer has also continued to map more of the galactic plane for the GLIMPSE360 project – more on that in a later post. Secondly, the Zooniverse now exists!

Everytime the Zooniverse and bubbles have been mentioned together, someone has been there saying that we should get the public to find and measure them. Whether this is between Chris, myself and others at Zooniverse HQ or between Grace Wolf-Chase at Adler Planetarium and various members of the ‘The Bubbling Galactic Disk‘ study. Bubbles and the Zooniverse should be a match made in the heavens.

Why are bubbles such a good target? For many reasons. They are not only amazing to look at, but also are numerous in the GLIMPSE data. They are tricky to measure but not impossibly hard. They are scientifically valuable objects to catalogue and measure the properties of, and they require more than one independent, human measurement to get a good handle on – this is key of course.

Many of the folks behind the ‘The Bubbling Galactic Disk‘ are part of the Project IX science team. We hope that everyone out there in the Zooniverse community can help refine and expand the existing bubble catalogue as part of Project IX. With the addition of new data, we also hope to find many new bubbles.

We are currently developing the bubble tool – the first user interface portion of the Project IX site  – which will have similarities to the Moon Zoo crater tool. We hope to be able to share it with you all soon so that you can help us to test and refine it. It is exciting to be able to involve everyone at this early stage.

If you’re interested in following this project and its take on bubbles, I’d suggest reading ‘The Bubbling Galactic Disk‘ and looking at the GLIMPSE website. If you have any questions – let us know. Bubble are just one thing we can see in the GLIMPSE data. More posts will follow about other scientifically useful objects lurking in this amazing infrared archive.

My Kingdom for a Science Case

It’s good to see this blog up and running. This is the first time we’ve written so explicitly about what we’re up to in planning and creating a Zooniverse project, and it’ll be interesting to see how it develops. We’ve normally kept quiet, not out of any desire to be secretive (well, maybe a little – we do enjoy surprising you) but because it’s worth it in order to increase our chances of getting attention from the press. I hope Project IX will demonstrate that we should be more open, more often and that we can talk more about what we’re up to.

As Project IX involves scanning beautiful images of star forming regions like the one above, it might not come as a surprise that the idea for it came from staring at the data. In conversations first with Grace, from the Adler Planetarium, and then with more and more of the star formation community, there was a real sense that there just *must* be something that could be gained by scanning these wonderful images.

Before we could start work on the Zoo, though, we had to be sure that there was a ‘science case’. As I’ve explained over on the Zooniverse blog, our one golden rule is that projects must be constructed so that we can be sure real science will result. In this case, many of the Zooniverse team have been directly involved – Rob and I both wrote PhD theses on star formation (in my case, this was back before I got distracted by galaxies) – but for other Zooniverse projects this has been the responsibility of a team of experts in the relevant field.

The criterion is simple : find a task which humans are not only capable of, but better at than existing computer programs. When I give talks about the Zoo, there are often computer scientists or computer minded people who insist that any given problem should be soluble. And many of them might well be – we’re even trying to improve things ourselves – but only after much hard work. We don’t have to beat the ideal machine learning algorithm – with the right incentives and enough money thrown at the problem, even hard tasks like optical character recognition can be solved – but only what’s out there now.

Of course, the task needs to be scientifically useful, too. Humans are probably better than computers at solving large jigsaw puzzles, but that doesn’t mean that there’s a Zooniverse project there.

There also needs to be enough data to keep all of you busy! If scientists have already reviewed most of the data, or if there wasn’t enough of it in the first place, then there may be little point having a Zoo. By making it easy to launch new projects, the Zooniverse makes smaller projects possible but there’s still a law of diminishing returns.

Wrestling with these problems has been quite tricky for Project IX. The search for the science case began with dark, dark clouds…