Alien stars pass close to home.Stars from an alien galaxy are raining down on our own Milky Way Milky Way, the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not blocked by the horizon, it would be seen as a circle around the entire sky. Although its motion is not readily apparent, the entire galaxy is rotating about the Milky Way's center. Relative to the universe, the galaxy is moving at a speed of c.370 mi per sec (c. and passing just a few hundred light-years from Earth. That's the conclusion of astronomers who have mapped the extent of the Sagittarius Sagittarius (săjĭtâr`ēəs) [Lat.,=the archer], constellation lying on the ecliptic (the sun's apparent path through the heavens) between Scorpius and Capricornus; it is one of the constellations of the zodiac. It is traditionally depicted as a centaur drawing his bow to release an arrow. dwarf galaxy, one of two dwarf galaxies that the Milky Way's gravity is ripping apart (SN: 11/15/03, p. 307). When a dwarf galaxy passes close to the Milky Way, its leading edge gets pulled more strongly by our galaxy's gravity than its trailing edge does. The unequal tugs stretch the dwarf, pulling stars out in spaghetti-like streams. A veil of dust in the Milky Way blocks visible light emanating from these streams, but infrared light punches through. Steven R. Majewski of the University of Virginia in Charlottesville and his colleagues mapped Sagittarius by selecting a group of infrared-bright stars. These M stars are rare in the outskirts of our galaxy but plentiful in the dwarf. The new map reveals that thousands of stars from Sagittarius are now passing through the region of the Milky Way in which the sun resides, the team reports in the Dec. 20 Astrophysical Journal. That's something of a cosmic coincidence because the sun and its environs take 240 million years to orbit the center of the Milky Way and intersect the Sagittarius stream for only a small fraction of that time. |
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