Free Astronomy Magazine July-August 2018

JULY-AUGUST 2018 said. “It’s a very orderly structure, whether it’s spiral arms or rings, and that’s particularly true with the youngest stellar populations.” On the other hand, there are multiple competing theories to connect the individual stars in indi- vidual star clusters to these ordered structures. “By seeing galaxies in very SPACE CHRONICLES galaxies and their most massive young stars and star clusters. The re- searchers also added archival visible-light images to provide a com- plete picture. The star cluster catalogs contain about 8,000 young clusters whose ages range from 1 million to roughly 500 million years old. These stellar groupings are as much as 10 times more massive than the largest clusters seen in our Milky Way galaxy. The star catalogs comprise about 39 million stars that are at least five times more massive than our Sun. Stars in the visible-light images are between 1 million and several billion years old; the youngest stars, those between 1 million and 100 million years old, shine prominently in ultraviolet light. The Hubble data provide all of the information to analyze these galaxies, the researchers explained. “We also are offer- ing computer models to help astronomers interpret the data in the star and cluster catalogs,” Sabbi said. “Researchers, for example, can investigate how star formation occurred in one specific galaxy or a set of galaxies. They can correlate the properties of the galaxies with their star formation. They can derive the star-formation history of the galax- ies. The ultraviolet-light images may also help astronomers identify the progenitor stars of supernovas found in the data.” One of the key questions the survey may help astronomers answer is the connection between star formation and the major structures, such as spiral arms, that make up a galaxy. “When we look at a spiral gal- axy, we usually don’t just see a random distribution of stars,” Calzetti NGC 3368 [NASA, ESA, and the LEGUS team] NGC 3627 [NASA, ESA, and the LEGUS team]