The formation of stars happens in large clouds of dust and gas, spread about in clumps and filaments inside galaxies. As young hot massive stars begin to shine, their powerful stellar winds sculpt these clouds, creating bubbles.

NASA’s Spitzer Space Telescope, the agency's flagship infrared telescope, has observed such a star-forming region in the constellation Aquila (the Eagle). Within the nebula, astronomers and citizen scientists have been able to identify 30 bubbles each between 10 and 30 light-years across.

It is difficult to estimate their true sizes because it is difficult to work out exactly how far away the cloud is, so astronomers used better-known bubbles to work out the properties of these new ones. Each bubble houses hundreds, if not thousands of stars, and infrared light is key to working that out.

Visible light is often blocked by the dust in stellar clouds, but infrared shines through. The different false colors of the images represent different infrared wavelengths, from which researchers can spot different features. Of course, the bubbles (in circles in the image below) are quite prominent, but the image also shows bow shocks (in squares). These arcs of warm dust are created when the stellar winds from a fast star slam into the surrounding material.

The image doesn’t just show these features either, it also shows background stars in blue, and the vast expanse of dust and organic molecules shining in green.

The beautiful image of the nebula is only a tiny demonstrable fraction of Spitzer's long career and only a small number of the infrared bubbles known to humanity. The Milky Way Project was set up by the Zooniverse collaboration to identify these bubbles. In the latest data release, citizen scientists identified 2,600 bubbles and 599 bow shocks, described in detail in a paper published in the Monthly Astronomical society.

Spitzer was first launched in 2003 and it has continuously operated ever since. Its 16-year mission is, unfortunately, coming to an end, however. It currently can only transmit for two and a half hours per day before its batteries are completely drained, so NASA has taken the decision to retire it on January 30, 2020.