Free Astronomy Magazine May-June 2026

23 MAY-JUNE 2026 T he differences in what Webb’s in- frared instruments re- veal and conceal within the PMR 1 “Exposed Cranium” nebula is ap- parent in this side-by- side view. More stars and background galax- ies shine through NIR- Cam’s view, while cosmic dust glows more prominently in MIRI’s mid-infrared. [NASA, ESA, CSA, STScI; Image Processing: Joseph De- Pasquale (STScI)] left and right hemi- spheres. Webb’s resolu- tion shows that this lane could be related to an outburst or outflow from the central star, which typically occurs as twin jets burst out in opposite directions. Evi- dence for this is particu- larly notable at the top of the nebula in Webb’s MIRI image, where it looks like the inner gas is being ejected out- ward. While there is still much to be understood about this nebula, it’s clear that it is being created by a star near the end of its fuel-burning “life.” In their end stages, stars expel their outer layers. It’s a dynamic and fairly fast process, in cosmic terms. Webb has captured a moment in this star’s de- cline. What ultimately happens will depend on the mass of the star, which is yet to be determined. If it’s massive enough, it will explode in a supernova. A less massive Sun-like star will continue to shed layers until only its core remains as a dense white dwarf, which will cool off over eons. ! N ebula PMR 1 is a cloud of gas and dust that bears an un- canny resemblance to a brain in a transparent skull, inspiring its nickname, the “Exposed Cranium” nebula. Webb captured its unusual features in both near- and mid-in- frared light. The nebula was first revealed in in- frared light by a predecessor to Webb, NASA’s now-retired Spitzer Space Telescope, more than a dec- ade ago. Webb’s advanced instru- ments show detail that enhances the nebula’s brain-like appearance. The nebula appears to have distinct regions that capture different pha- ses of its evolution — an outer shell of gas that was blown off first and consists mostly of hydrogen, and an inner cloud with more structure that contains a mix of different gases. Both Webb’s NIRCam (Near- Infrared Camera) and MIRI (Mid-In- frared Instrument) show a dis- tinctive dark lane running vertically through the middle of the nebula that defines its brain-like look of