Free Astronomy Magazine July-August 2021

16 JULY-AUGUST 2021 ASTRO PUBLISHING own Milky Way, which has a diameter of 100,000–200,000 light-years. In other ways, however, the Southern Pin- wheel probably gives a good approximation of how our Milky Way would look to a dis- tant alien civilization. Six different filters were used on DECam in order to create this spectacular new view of a classical beauty. Filters allow astronomers to select which wavelengths of light they wish to view the sky in. This is cru- cial for science observations, when astronomers require very specific information about an object, but it also allows color- ful images like this one to be created. Observing celestial objects — such as the Southern Pinwheel — with several dif- ferent filters means that different details can be picked out. For example, the dark tendrils curl- ing through the galaxy are actually lanes of dust, blocking out light. In contrast, the clustered, bright red spots are caused by glowing, hot hydrogen gas (which identifies these as hubs of star formation). Dusty trails and dynamic ionized gas have different temperatures, and are therefore visible in different wavelengths. Filters allow both to be observed separately, and then combined into one intricate image. In all, 163 DECam exposures, with a total com- bined exposure time of over 11.3 hours, went into creating this por- trait of Messier 83. Yet these observations were not just about creating a pretty picture. They are helping to prepare for up- coming observations by Vera C. Rubin Observatory, a future pro- gram of NOIRLab. In ten years of operation, starting in 2023, Rubin Observatory will carry out an un- precedented optical survey of the C osmoView Episode 22: The spiral of the Southern Pinwheel. [Images and Videos: CTIO/NOIRLab/DOE/NSF/AURA, M. Soraisam (University of Illinois), /LBNL/DECam/R. Hahn, R. Sparks. Image processing: Travis Rector (University of Alaska Anchorage), Mahdi Zamani & Davide de Martin. Music: Stellardrone - Airglow] visible sky named the Legacy Survey of Space and Time (LSST). “The Messier 83 observations are part of an ongoing program to produce an atlas of time-varying phenomena in nearby southern galaxies in prepa- ration for Rubin Observatory’s Legacy Survey of Space and Time,” said Monika Soraisam of the Univer- sity of Illinois, who is the principal investigator for DECam’s observa- tions of Messier 83. “We are gener- ating multi-color light curves of stars in this galaxy, which will be used to tame the onslaught of alerts expected from LSST using state-of-the-art software infrastruc- ture such as NOIRLab’s own ANTARES alert-broker.” Built by the US Department of En- ergy (DOE), DECam is mounted on the Víctor M. Blanco 4-meter Tele- scope at CTIO in Chile. DECam is a powerful instrument that uses 74 highly sensitive charge-coupled de- vices (CCDs) to take images. CCDs are the same devices that are used to take photos in everyday cell phones. Of course, the CCDs in DECam are much larger, and they were specifically designed to collect very faint red light from distant galaxies. This capability was crucial for DECam’s original purpose, the Dark Energy Survey. This ambitious survey probed one of the most fun- damental questions of the Universe — why is our Universe not only ex- panding, but expanding at an accel- erating rate? For six years DECam surveyed the skies, imaging the most distant galaxies to collect more data to enable astronomers to further investigate our accelerating Universe. Taking beautiful images such as this one must seem a lot simpler for DECam. “While DECam has fulfilled its orig- inal goal to complete the Dark En- ergy Survey, it continues to be a valuable resource for the astronom- ical community, capturing sweeping views of objects like Messier 83 that both delight the senses and ad- vance our understanding of the Universe,” said Chris Davis, Program Director for NOIRLab at the Na- tional Science Foundation. !