M27: 不是彗星

2019 August 29

M27: Not a Comet
Image Credit & Copyright: Bob Franke

Explanation: While hunting for comets in the skies above 18th century France, astronomer Charles Messier diligently kept a list of the things he encountered that were definitely not comets. This is number 27 on his now famous not-a-comet list. In fact, 21st century astronomers would identify it as a planetary nebula, but it’s not a planet either, even though it may appear round and planet-like in a small telescope. Messier 27 (M27) is an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core. The nebula forms as the star’s outer layers are expelled into space, with a visible glow generated by atoms excited by the dying star’s intense but invisible ultraviolet light. Known by the popular name of the Dumbbell Nebula, the beautifully symmetric interstellar gas cloud is over 2.5 light-years across and about 1,200 light-years away in the constellation Vulpecula. This impressive color composite highlights details within the well-studied central region and fainter, seldom imaged features in the nebula’s outer halo. It incorporates broad and narrowband images recorded using filters sensitive to emission from hydrogen and oxygen atoms.

M27: 不是彗星
影像来源与版权: Bob Franke

说明：当天文学家查尔斯.梅西耶在18世纪的法国天空中寻找彗星时，他将所看到的一些肯定不是彗星的天体认真地编录成册。以上这个就是现在著名的非彗星名册中的第27号天体。实际上，21世纪的天文学家会将它分类为行星状星云，但它也不是行星，只是我们用小型望远镜观测时，它看起来具有圆形和行星状而已。M27是气体发射星云的一个典型例子，它是类似太阳的恒星耗尽了其核心的核燃料后所产生的。当恒星的外层被抛入太空时，外层中的原子受到垂死恒星发出的强烈但不可见的紫外光激发而辐射出可见光，便形成了这个星云。这个美丽对称的星际气体云也被俗称为哑铃星云，它位于狐狸座内，大小超过2.5光年，距离我们约1200光年远。这幅令人印象深刻的彩色合成影像呈现了经过充分研究的中心区域以及星云外晕中、较黯淡且很少被拍摄到的细致结构。该影像是由使用滤波器拍摄的宽波段和窄波段照片结合而成，记录了氢原子和氧原子发出的辐射。