哈勃望远镜收藏了一袋满满的星星
Many colorful stars are packed close together in this image of the globular cluster NGC 1805, taken by the NASA/ESA Hubble Space Telescope. This tight grouping of thousands of stars is located near the edge of the Large Magellanic Cloud, a satellite galaxy of our own Milky Way. The stars orbit closely to one another, like bees swarming around a hive. In the dense center of one of these clusters, stars are 100 to 1,000 times closer together than the nearest stars are to our Sun, making planetary systems around them unlikely.
The striking difference in star colors is illustrated beautifully in this image, which combines different types of light: blue stars, shining brightest in near-ultraviolet light, and red stars, illuminated in red and near-infrared. Space telescopes like Hubble can observe in the ultraviolet because they are positioned above Earth’s atmosphere, which absorbs most ultraviolet light, making it inaccessible to ground-based facilities.
This young globular cluster can be seen from the Southern Hemisphere, in the Dorado constellation, which is Portuguese for dolphinfish. Usually, globular clusters contain stars that are born at the same time. NGC 1805, however, is unusual as it appears to host two different populations of stars with ages millions of years apart. Observing such clusters of stars can help astronomers understand how stars evolve, and what factors determine whether they end their lives as white dwarfs or explode as supernovae.
Text credit: ESA (European Space Agency)
Image credit: ESA/Hubble & NASA, J. Kalirai
NASA / ESA哈勃太空望远镜拍摄的这张球状星团NGC 1805的图片中，许多五颜六色的星星紧紧地排列在一起。数千颗恒星组成的紧密星团位于大麦哲伦星云的边缘附近，麦哲伦星云是我们银河系的卫星星系。星星彼此紧紧围绕，就像蜜蜂在蜂巢周围成群结队一样。在其中一个星团的密集中心，恒星之间的距离比离我们最近的恒星的距离近100到1,000倍，这使得它们周围不可能有行星系。
在这张结合了不同类型光线的照片中，恒星颜色的显著差异得到了完美的展示：蓝色的恒星在近紫外光下发出最亮的光，而红色的恒星在红光和近红外的照射下发出最亮的光。像哈勃这样的太空望远镜之所以能观测到紫外线，是因为它们位于地球大气层之上，而大气层吸收了大部分紫外线，使得地面设施无法接收到这些紫外线。
从南半球的多拉多星座(Dorado constellation)可以看到这个年轻的球状星团，多拉多星座在葡萄牙语中是海豚鱼的意思。通常，球状星团包含同时诞生的恒星。然而NGC 1805却不同寻常，因为它似乎拥有两个年龄相差数百万年的不同恒星群。观察这样的星团可以帮助天文学家了解恒星是如何演化的，以及什么因素决定了它们是作为白矮星结束生命还是作为超新星爆炸。
文字来源：ESA（欧洲航天局）
图片来源：ESA/Hubble & NASA, J. Kalirai