猫眼星云的外晕
Halo of the Cat’s Eye
Image Credit & Copyright: Bray Falls
Explanation: What created the unusual halo around the Cat’s Eye nebula? No one is sure. What is sure is that the Cat’s Eye Nebula (NGC 6543) is one of the best known planetary nebulae on the sky. Although haunting symmetries are seen in the bright central region, this image was taken to feature its intricately structured outer halo, which spans over three light-years across. Planetary nebulae have long been appreciated as a final phase in the life of a Sun-like star. Only recently however, have some planetaries been found to have expansive halos, likely formed from material shrugged off during earlier puzzling episodes in the star’s evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of the Cat’s Eye Nebula’s halo to be 50,000 to 90,000 years.
Tomorrow’s picture: herculean stars
猫眼星云的外晕
影像提供与版权: Bray Falls
说明: 是什么造成了猫眼星云周围的不寻常外晕？目前没人能给个明确的答案。不过很可确定的，猫眼星云 (NGC 6543）是地球天空最著名的行星状星云之一。虽然猫眼星云有个形状对称、引人注目的明亮中心区，然而这张影像的主题，则是要突显它结构错综复杂、宽度超过3光年的外晕。虽然人们早就知道行星状星云，是类太阳恒星生命历程里的最后一章，不过，发现部份行星状星云外晕则是相对晚近的事。而这种外晕，很可能是恒星在谜样的演化初期所抛出的物质。行星状星云阶段持续的期间，被认为大约只有10,000年，而天文学家估计猫眼星云的丝缕状外晕结构，年龄则介于50,000到90,000年之间。
明日的图片: herculean stars
