Cited research: Astrophys. J. 715, 1370–1382 (2010)

Stars are born inside giant clouds of gas. Figuring out where such clouds begin and end is tricky because their main component, molecular hydrogen (H2), is often too cold to be seen by telescopes.

Paul Goldsmith and his colleagues at NASA's Jet Propulsion Laboratory in Pasadena, California, have used the orbiting Spitzer Space Telescope to find the edge of a nearby molecular cloud. By detecting emissions from transitions in the rotational states of molecular hydrogen, they found hints of a warm layer of H2 on the surface of the cloud. The team suggests that the properties of the hot edge could be related to circulation of gas within the cloud. G.B.