Free Astronomy Magazine July-August 2018

35 JULY-AUGUST 2018 SPACE CHRONICLES formation on young, massive stars and star clusters, and how their environment affects their develop- ment. “There has never before been a star cluster and a stellar catalog that included observations in ultravi- olet light,” explained survey leader Daniela Calzetti of the University of Massachusetts, Amherst. “Ultra- violet light is a major tracer of the youngest and hottest star populations, which astronomers need to derive the ages of stars and get a complete stellar his- tory. The synergy of the two catalogs combined offers an unprecedented potential for understanding star formation.” How stars form is still a vexing question in astronomy. “Much of the light we get from the universe comes from stars, and yet we still don’t understand many as- pects of how stars form,” said team member Elena Sabbi of the Space Telescope Science Institute in Bal- timore, Maryland. “This is even key to our existence — we know life wouldn’t be here if we didn’t have a star around.” The research team carefully selected the LEGUS tar- gets from among 500 galaxies, compiled in ground- based surveys, located between 11 million and 58 million light-years from Earth. Team members chose the galaxies based on their mass, star-formation rate, and abundances of elements that are heavier than hy- drogen and helium. The catalog of ultraviolet objects collected by NASA’s Galaxy Evolution Explorer (GALEX) spacecraft also helped lay the path for the Hubble study. The team used Hubble’s Wide Field Camera 3 and the Advanced Camera for Surveys over a one-year period to snap visible- and ultraviolet-light images of the Hubble observations with archival Hubble images for 50 star-forming spiral and dwarf galaxies in the local universe, offering a large and extensive resource for understand- ing the complexities of star forma- tion and galaxy evolution. The project, called the Legacy Extra- Galactic UV Survey (LEGUS), has amassed star catalogs for each of the LEGUS galaxies and cluster cat- alogs for 30 of the galaxies, as well as images of the galaxies them- selves. The data provide detailed in- UGCA 281 [NASA, ESA, and the LEGUS team] NGC 4258 [NASA, ESA, and the LEGUS team ]