A combination of data from NASA’s Spitzer Space Telescope and ESA’s Herschel Space Observatory has produced this more complete image of star formation in the Orion Nebula. Spitzer data cover shorter infrared wavelengths than Herschel, but combining the two, as in this false-colour image, can show the temperatures of dust in a region of star formation. Warmer objects picked out by Spitzer (at 8 and 24 mm) are shown in blue, while progressively colder regions from Herschel data show in green and then red (70 and 160 mm respectively). Repeated observations with Herschel (weekly for six weeks in the spring of 2011) showed that the brightness of the young stars varied by as much as 20%. This is puzzling because it represents fast changes in relatively cool dust, probably in the outer disc or gas envelope far from the hot young star itself.
How does material that is relatively cool and far from the star heat up so quickly? Models of star formation suggest timescales of hundreds of years, rather than a matter of weeks. One possibility is that lumpy filaments of gas funnel from the outer to the central regions of the star, temporarily warming the object as the clumps hit its inner disc. Or perhaps material occasionally piles up at the inner edge of the disc and casts a shadow on the outer disc.