Free Astronomy Magazine September-October 2016

SPACE CHRONICLES the duo may have encountered a ga- seous filament, which compresses gas in the galaxies and stokes star birth. Based on the galaxies' locations, Tol- lerud's team determined that the ob- jects are at the edge of a nearby fila- ment of dense gas. Each galaxy con- tains about 10 million stars. Hubble uncovers a galaxy pair coming in from the wilderness by NASA N ASA's Hubble Space Telescope has uncovered two tiny dwarf galaxies that have wandered from a vast cosmic wilderness into a nearby “big city” packed with gal- axies. After being quiescent for bil- lions of years, they are ready for partying by starting a firestorm of star birth. “These Hubble images may be snapshots of what present- day dwarf galaxies may have been like at earlier epochs,” said lead re- searcher Erik Tollerud of the Space Telescope Science Institute in Balti- more, Maryland. “Studying these and other similar galaxies can pro- vide further clues to dwarf galaxy formation and evolution.” The Hubble observations suggest that the galaxies, called Pisces A and B, are late bloomers because they have spent most of their existence in the Local Void, a region of the uni- verse sparsely populated with gal- axies. The Local Void is roughly 150 million light-years across. Under the steady pull of gravity from the galactic big city, the loner dwarf galaxies have at last entered a crowd- ed region that is denser in interga- lactic gas. In this gas-rich environ- ment, star birth may have been trig- gered by gas raining down on the galaxies as they plow through the denser region. Another idea is that P isces A is 18.4 million light-years away. In this image of the galaxy, the bright object at the top is a more distant background galaxy. Other distant back- ground galaxies are visible as bright dots. [NASA, ESA, and E. Tollerud (STScI)]