<P> Aside from their different structure and lower mass, they differ from our galaxy in two major ways . First, they are gas - rich; a higher fraction of their mass is hydrogen and helium compared to the Milky Way . They are also more metal - poor than the Milky Way; the youngest stars in the LMC and SMC have a metallicity of 0.5 and 0.25 times solar, respectively . Both are noted for their nebulae and young stellar populations, but as in our own galaxy their stars range from the very young to the very old, indicating a long stellar formation history . </P> <P> The Large Magellanic Cloud was host galaxy to a supernova (SN 1987A), the brightest observed in over four centuries . </P> <P> Measurements with the Hubble Space Telescope, announced in 2006, suggest the Magellanic Clouds may be moving too fast to be long term companions of the Milky Way . If they are in orbit, that orbit takes at least 4 billion years . They are possibly on a first approach and we are witnessing the start of a galactic merger that may overlap with the Milky Way's expected merger with the Andromeda Galaxy (and perhaps the Triangulum Galaxy) in the future . </P> <P> Astrophysicists D.S. Mathewson, V.L. Ford and N. Visvanathan proposed that the SMC may in fact be split in two, with a smaller section of this galaxy behind the main part of the SMC (as seen from Earth's perspective), and separated by about 30,000 light years . They suggest the reason for this is due to a past interaction with the LMC splitting the SMC, and that the two sections are still moving apart . They have dubbed this smaller remnant the Mini Magellanic Cloud . </P>

What are the magellanic clouds what happened in the lmc in 1987