The Asymmetric Nebula Surrounding Wolf-Rayet Star 18
Image Credit & Copyright: Alex Woronow
Explanation: Why does the nebula around the star WR-18 shine brighter on one side? Also known as NGC 3199, this active star and its surrounding nebula lie about 12,000 light-years away toward the nautical southern constellation of Carina. The featured deep image has been highly processed to bring out filamentary details of the glowing gas in the bubble-shaped nebula. The nebula is about 75 light-years across. Near the nebula’s center is a Wolf-Rayet star, WR-18, which is a massive, hot, short-lived star that generates an intense and complex stellar wind. In fact, Wolf-Rayet stars are known to create nebulas with interesting shapes as their powerful winds sweep up surrounding interstellar material. In this case, the bright right edge was initially thought to indicate that a bow shock was being produced as the star plowed through a uniform medium, like a boat through water. Recent measurements and analyses, however, have shown the star is not moving quickly toward the bright edge. A more likely explanation has emerged that the material surrounding the star is not uniform, but clumped and denser near the bright edge.
Tomorrow’s picture: open space
图像提供与版权: Alex Woronow
说明: 为何恒星WR-18周围的星云，有一侧较明亮呢？环拱在这颗活跃恒星周围的星云名为NGC 3199，座落在南天的船底座方向约12,000光年远处。这幅主题深空图像经过特别处理，以突显这团直径约75光年的气泡星云里的发光气体之细丝状构造。在星云中心附近的沃夫-瑞叶恒星（WR-18），则是一颗会发出强烈复杂恒星风的大质量炽热短命恒星。事实上如众所周知的，当沃夫-瑞叶恒星的强烈恒星风扫过周围的星际物质，往往会产生形状很有趣的星云。在此案例里，星云较明亮的右缘，起初认为是源自恒星穿过均匀介质所产生的弓形震波，情况类似船滑过水面的景观。然而，最近的测量和分析证实这颗恒星并非高速向亮边移动。于是就出现了另一种更可能的解释：恒星周围的物质分布并不均匀，而是亮边附近的物质较密集。
明日的图片: open space