346个 Rings and Bar of Spiral Galaxy NGC 1398Image Credit: Mark Hanson; Data: Mike SelbyExplanation: Why do some spiral galaxies have a ring around the center? Spiral galaxy NGC 1398 not only has a ring of pearly stars, gas and dust around its center, but a bar of stars and gas across its center, and spiral arms that appear like ribbons farther out. The featured deep image from Observatorio El Sauce in Chile shows the grand spiral galaxy in impressive detail. NGC 1398 lies about 65 million light years distant, meaning the light we see today left this galaxy when dinosaurs were disappearing from the Earth. The photogenic galaxy is visible with a small telescope toward the constellation of the Furnace (Fornax). The ring near the center is likely an expanding density wave of star formation, caused either by a gravitational encounter with another galaxy, or by the galaxy’s own gravitational asymmetries.影片提供: Mark Hanson; 数据: Mike Selby说明: 为何有些螺旋星系有拱心环呢？这幅来自智利埃尔绍塞天文台主题深空影像，无比清晰的解析了宏伟的螺旋星系NGC 1398。在影像里，螺旋星系NGC 1398的中心，不但有个珍珠环状的恒星、气体和尘埃，还有一道横亘过中心的恒星和气体长棒，而较外围的旋臂也形似缎带。NGC 1398的距离大约有6千5百万光年远，也就是说我们现在所见到的光，大约在恐龙正从地球消失时，就从这个星系出发。这个位在天炉座方向、用小望远镜即可见的美丽星系，核心附近的内环构造，可能是恒星诞生活动造成的扩张密度波，触发源则可能是此星系和另一个星系近距离接近的引力互扰，或者是由于它本身的引力不对称。
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