NGC 7789: 卡罗琳的玫瑰星团

2024年7月6日

NGC 7789: Caroline’s Rose
Image Credit & Copyright: Massimo Di Fusco

Explanation: Found among the rich starfields of the Milky Way, star cluster NGC 7789 lies about 8,000 light-years away toward the constellation Cassiopeia. A late 18th century deep sky discovery of astronomer Caroline Lucretia Herschel, the cluster is also known as Caroline’s Rose. Its visual appearance in small telescopes, created by the cluster’s complex of stars and voids, is suggestive of nested rose petals. Now estimated to be 1.6 billion years young, the galactic or open cluster of stars also shows its age. All the stars in the cluster were likely born at the same time, but the brighter and more massive ones have more rapidly exhausted the hydrogen fuel in their cores. These have evolved from main sequence stars like the Sun into the many red giant stars shown with a yellowish cast in this color composite. Using measured color and brightness, astronomers can model the mass and hence the age of the cluster stars just starting to “turn off” the main sequence and become red giants. Over 50 light-years across, Caroline’s Rose spans about half a degree (the angular size of the Moon) near the center of the sharp telescopic image.

Tomorrow’s picture: cloudy skies

NGC 7789: 卡罗琳的玫瑰星团
影像提供与版权: Massimo Di Fusco

说明: 在仙后座方向的银河富星场里，可见到大约8,000光年远的星团NGC 7789。它是天文学家卡罗琳·卢克雷蒂娅·赫歇尔于18世纪末所发现的深空天体，因此这个星团有卡罗琳的玫瑰星团之称。而它在小望远镜里深具暗示性的重瓣外观，则是由星团里的拥挤成员星和空洞所交织而成。这个疏散星团目前的推估年龄大约为16亿年，所以有些成员星已现出老态。这个星团内的所有恒星，可能都诞生于同一时期，但较亮且较大质量的恒星，也较快地用完核心的燃料。在这幅美丽的彩色合成影像里，这些恒星已经从像太阳这样的主星序恒星，演化成为带着泛黄色泽的红巨星。根据量测的色泽和亮度，天文学家可以计算星团内何种质量（即何种年龄）的恒星，会开始离开主星序变成红巨星。在这幅清晰的望远镜影像里，宽超过50光年的”卡罗琳的玫瑰星团“之跨幅约为半度，大约和满月的张角相当。 （Caroline’s Rose 卡罗琳的玫瑰星团）

明日的图片: cloudy skies