Free Astronomy Magazine November-December 2014

GALAXIES 32 NOVEMBER-DECEMBER 2014 The recent study of an ultra-compact galaxy has shown that those very dense stellar systems are not an enlarged version of globular clusters, but rather the remnants of large galaxies stripped of their mat- ter outside the nucleus by even bigger galaxies. The true na ultra-compa W hen we talk about galaxies, we generally refer to vast stellar sys- tems whose vastness is difficult even to imagine. Not all galaxies though are infinite, as there are also relatively small ones which astronomers call dwarfs. Among these there is a very particular class dubbed “ultra-compact dwarfs” (UCD), typically less than a few hundred light-years across and characterized by high stellar density, compa- rable to that of globular clusters, and a bright- ness similar to that of the nuclei of large gal- axies. The similarity of UCDs with stellar sys- tems of different nature has divided astron- omers about their classification, as there is who considers them a particularly massive