Galactic Champagne: bubbles, star formation, pretty pictures, and citizen scientists!

A sample image used by citizen scientists to locate "bubbles" in
the Milky Way. (left) raw image; (center) image showing work
of some of the volunteers; (right) the final image showing which
features have met the criteria for being "bubbles." Full explanation
in the text. Image: NASA/JPL-Caltech/Oxford University

More than 35,000 "citizen scientists" have identified 5,000 "bubbles" in images of our galaxy.  (Wouldn't it be wonderful if even a fraction of these people found this blog!!) Their work has increased the number of such objects that have been identified by a factor of 10. More details about the Milky Way Project can be found here by following the "Click here" link. According to the statistics listed at the bottom of the page, 527,000 images have been examined, and 662,000 bubbles have been drawn.

Each citizen scientist takes an image, and draws circles, arcs, fractions of circles, and identifies other features, using a special drawing program, not unlike many of the commercial drafting packages, just customized to this specific effort.  A special tool allows the researcher to draw a circular band around an object, center it on the object, alter the width of the band, and change its shape (e.g., toward an ellipse, or to allow an indent on some segment of it). Since circles may overlap, other tools allow fractions of a circle to be identified.  After doing this, the researchers can flag the image as one of their "favorites", and move on to another image. It all seems like great fun, which is at least partially what science should be about! I don't know if they are still accepting new citizen scientists into the project, but details are on the link provided in the first paragraph.

Each citizen scientist creates an edited image showing the circles and segments that they have identified.  These are laid on top of each other to create a so-called "heat map," the middle image above. Features that have been identified by many users then jump out as being the brightest on the heat maps. At least five volunteers must flag a "candidate bubble" before it is included in the final catalogue of bubbles (right). The brightness of the bubble in the catalog is determined by its "hit rate," the fraction of users that traced it out (for some reason, this reminds me of a beauty contest, with elements of both beauty and popularity....). The faintest ones in the image above were identified by about 10% of the researchers, the solid ones by 50% or more.

The data come from two instruments on Spitzer: the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (fortunately abbreviated to GLIMPSE--and makes me appreciate the addition of "Extraordinaire" to the instrument name! Someone has a sense of humor), and the Multiband Imaging Photometer for Spitzer Galactic (MIPSGAL) surveys. Spitzer is a space telescope launched in 2003, the "final element in NASA's Great Observatories Program." The wavelength covered is 3-180 microns, that is, in the infrared region of the spectrum.  It catches thermal radiation emitted from objects. Spitzer is, currently 161 million kilometers from the earth.

Young, hot stars blow bubbles into the gas and dust of the Milky Way. What are the bubbles? Interestingly, the press release doesn't discuss this at all, and although the press release gives the "authors of the paper," it doesn't say what paper, or where it was published. (Grrrr....come on, press offices, at least give us a hint...). As far as I can tell, when young stars coalesce out of the spinning gas and dust in the galaxy, they collapsing in on themselves due to their own weight.  This process generates heat and sets up the combustion in the young stars. Excess material appears to be shed in order to slow down the rotation of the clump, and to prevent it from breaking apart.  Traditionally, it was thought that the stars shed this material in the form of a pair supersonic jet streams, not as spherical bubbles.  Now it appears that the bubbles may be the excess material.   

The distribution of bubbles in 3-D is interesting and potentially provides hints about structure in the Milky Way. For example, there are more bubbles off-center of the Milky Way than in its center. This has surprised the scientists because they expected star formation to be strongest where the most dense gas is, that is, at the center. This is a fairly new and exciting area of astronomy (the last 5 years?) and is clearly going to take me more time for me to sort this out.