Stars are born in celestial factories known as molecular clouds. Dark, dense, and cool, these clouds absorb light at visible wavelengths, making them hard to comprehensively survey with optical telescopes. But thanks to the ALMA radio telescope in Chile, astronomers were able to map these stellar nurseries in stunning detail, observing 90 nearby galaxies at radio wavelengths.
The result is an unprecedented census of the demographics of molecular clouds: A total of 40,000 examples were identified in total (20 times more than previously known), with their locations pinpointed to a dizzyingly diverse array of galaxies. As seen in the image above, these stellar factories trace out a ghostly outline of star-forming activity in their galaxies, like cities blazing at night seen from space, separated by vast obscurities of darkness.
The survey, known as PHANGS (short for Physics at High Angular Resolution in Nearby GalaxieS), was made possible by the high resolution of ALMA.