The Magellanic Clouds
The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are two of the Milky Way's closest neighbouring galaxies. A stunning sight in the southern hemisphere, they were named after Ferdinand Magellan, who explored those waters in the 16th century.
For hundreds of years, these galaxies were considered satellites of the Milky Way, gravitationally bound to our home galaxy.
Although they look like glowing clouds to the unaided eye, the LMC and SMC are both irregular galaxies. The Large Magellanic Cloud is located approximately 160,000 light-years from Earth. It's about one-twentieth as large as our galaxy in diameter and holds about one-tenth as many stars. The Small Magellanic Cloud is located around 200,000 light-years from Earth. It's about ten times smaller than its companion and two hundred times smaller than the Milky Way.
Earlier this year, CfA astronomers reported measuring the 3-d velocities of the Magellanic Clouds through space with greater accuracy than ever before. The velocities were anomalously high.
Two explanations were proposed:
1) the Milky Way is more massive than previously thought, or 2) the Magellanic Clouds are not gravitationally bound to the Milky Way.
Further analysis verified the second explanation. The parabolic orbit calculated for the Clouds, based on the observed velocities, shows that both are on their first pass by the Milky Way.
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