Andromeda's New Satellite Galaxy Is Faintest Yet

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<b>Andromeda's New Satellite Galaxy Is Faintest Yet</b><br /><br />LINK<br /><br />The faintest satellite galaxy yet found around the Milky Way's near-twin, Andromeda, has been turned up by the Sloan Digital Sky Survey. The discovery suggests other dim galaxies remain undetected and goes some way towards solving a mystery known as the "missing satellite" problem.<br /><br />Standard theories of dark matter and the evolution of galaxies calculate that small galaxies should merge over time to form large ones, and that many of these undersized, unmerged galaxies should be visible today. <br /><br />The trouble is that theories predict about 100 times more dwarf galaxies than are actually observed – a discrepancy known as the missing satellite problem. So astronomers have come up with several theories to explain the difference. These range from the possibility that small galaxies somehow inhibit star formation, making them essentially invisible, to the prospect that they are surrounded by more unseen dark matter than first thought.<br /><br />But since 2004, astronomers have discovered the two faintest galaxies ever seen – UMajor around our Milky Way and Andromeda IX around our nearest large galactic neighbour, Andromeda. These finds suggested the missing satellite problem may actually be less dire than originally thought. <br /><br />Now, researchers led by Daniel Zucker, who completed the work while at the Max Planck Institute for Astronomy in Heidelberg, Germany, has found another dim dwarf galaxy called Andromeda X – the faintest satellite known around that galaxy. The dwarf appears to lie about 280,000 to 450,000 light years from Andromeda, which itself lies just 2.5 million light years from the Milky Way. <br /><br />Systematic mapping<br />"Up until a few years ago, people thought we had found all the galaxies in the Local Group [a small cluster of neighbouring galaxies including the Milky Way],"