Free Astronomy Magazine July-August 2015

COSMOLOGY in an era in which the universe was affect- ed by powerful waves of star formation, which deeply changed the then existing young galaxies. Astronomers study with particular attention these remote objects, for understanding how we got to our con- temporary universe. SDP.81 was one of the targets being observ- ed in October 2014 with the Atacama Large Millimeter/submillimeter Array (ALMA) to test the performance in high-resolution mode of that array of 66 parabolic anten- nas operating, as the name suggests, in the millimeter and sub- millimeter domains. (ALMA uses the prin- ciples of interferom- etry, in that its an- tennas work in syn- chrony and collect photons as if they were a single giant antenna: the resul- tant resolution is vir- tually that of an in- strument whose size is equivalent to the maximum distance between the anten- nas themselves, even though the amount of collected light is proportional only to the total area of the antennas.) The images of SDP.81 obtained at 1 millimeter wavelength appeared im- mediately extraordinary for the richness of details, and the same goes for the spectra recorded during the observations, which allowed to highlight the internal motions of individual regions of the deformed gal- axy, understand how the whole system ro- tates and also estimate its mass. Such a rich gathering of information is the result of the extremely high-resolution that ALMA T he lensed ring of SDP.81 in three different versions: bottom, the image taken by ALMA showing the light emitted by the dust of the galaxy; centre, as the first, but with the addition of the light emitted by the carbon monoxide record- ed by ALMA; top, as the second, but with the addition of the light emit- ted by the inter- posed galaxy as seen with Hubble. [ALMA (NRAO/ESO /NAOJ)B. Saxton NRAO/AUI/NSF; NASA/ESA Hub- ble, T. Hunter (NRAO)] S ome of the 66 antennas of 12 and 7 meters diameter that make up ALMA, the most pow- erful instrument available to astronomers today. [ALMA (ESO/NAOJ/NRAO), O. Dessibourg]