描述M27 Knots.jpg	Close up detail of knots in planetary nebula Messier 27
日期	2001年11月
来源	http://hubblesite.org/newscenter/archive/releases/2003/06/image/a (direct link)
作者	C.R. O'Dell (Vanderbilt University)
授权 (二次使用本文件)	Public domainPublic domainfalsefalse 本文件完全由NASA创作，在美国属于公有领域。根据NASA的版权方针，NASA的材料除非另有声明否则不受版权保护。（参见Template:PD-USGov/zh、NASA版权方针页面或JPL图片使用方针。） 警告: 使用NASA的标志、徽章、徽标等受到美国法律14 CFR 1221的限制。 NASA网站大量存储来自苏联或俄罗斯航天机构的图片，以及其他非美国的航天机构图片。这些文件不一定属于公有领域。 根据哈勃空间望远镜的数据制作的材料，如果不是明确声明由STScI提供，则可能受到版权保护。[1]参见{{PD-Hubble}}和{{Cc-Hubble}}。 SOHO（ESA和NASA）联合项目表示，由旗下的探测器创作的材料受版权保护，且对于商业性非教育目使用材料需要授权。[2] 每日一天文图（APOD）网站上展示的图片可能受到版权保护。[3] 国家太空科学数据中心（NSSDC）网站据信存储了受版权保护内容。其图库常见问答表明除非另有声明，图库的所有图片都属于公有领域。

Picture shows a 99″.5 × 75″.5 section of the central region of M 27.^[1]

From the NASA source site [4]:

An aging star's last hurrah is creating a flurry of glowing knots of gas that appear to be streaking through space in this close-up image of the Dumbbell Nebula, taken with NASA's Hubble Space Telescope.

The Dumbbell, a nearby planetary nebula residing more than 1,200 light-years away, is the result of an old star that has shed its outer layers in a glowing display of color. The nebula, also known as Messier 27 (M27), was the first planetary nebula ever discovered. French astronomer Charles Messier spotted it in 1764.

The Hubble images of the Dumbbell show many knots, but their shapes vary. Some look like fingers pointing at the central star, located just off the upper left of the image; others are isolated clouds, with or without tails. Their sizes typically range from 11 - 35 billion miles (17 - 56 billion kilometers), which is several times larger than the distance from the Sun to Pluto. Each contains as much mass as three Earths.

The knots are forming at the interface between the hot (ionized) and cool (neutral) portion of the nebula. This area of temperature differentiation moves outward from the central star as the nebula evolves. In the Dumbbell astronomers are seeing the knots soon after this hot gas passed by.

Dense knots of gas and dust seem to be a natural part of the evolution of planetary nebulae. They form in the early stages, and their shape changes as the nebula expands. Similar knots have been discovered in other nearby planetary nebulae that are all part of the same evolutionary scheme. They can be seen in Hubble telescope photos of the Ring Nebula (NGC 6720), the Eskimo Nebula (NGC 2392) and the Retina Nebula (IC 4406). The detection of these knots in all the nearby planetaries imaged by the Hubble telescope allows astronomers to hypothesize that knots may be a feature common in all planetary nebulae.

This image, created by the Hubble Heritage Team (STScI), was taken by Hubble's Wide Field Planetary Camera 2 in November 2001, by Bob O'Dell (Vanderbilt University) and collaborators. The filters used to create this color image show oxygen in blue, hydrogen in green and a combination of sulfur and nitrogen emission in red.

Object Names: Dumbbell Nebula, M27, NGC 6853

Image Type: Astronomical

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)

Acknowledgment: C.R. O'Dell (Vanderbilt University)