描述M27 Knots.jpg	Close up detail of knots in planetary nebula Messier 27
日期	2001年11月
來源	http://hubblesite.org/newscenter/archive/releases/2003/06/image/a (direct link)
作者	C.R. O'Dell (Vanderbilt University)
授權許可 (重用此檔案)	Public domainPublic domainfalsefalse 本作品由NASA創作，屬於公有領域。根據NASA的版權政策：“NASA的創作除非另有聲明否則不受版權保護。”（參見：Template:PD-USGov/zh，NASA版權政策或JPL圖像使用政策） 警告: 使用NASA的logo，徽標等受到美國法律14 CFR 1221的限制。 NASA網站還提供大量來自蘇聯/俄羅斯航天機構，以及其他非美國的太空機構的圖像。這些圖像不一定屬於公有領域。 根據哈勃空間望遠鏡的數據制作的素材，如果不是明確聲明由STScI提供，則可能受到版權保護。[1] 參看{{PD-Hubble}}和{{Cc-Hubble}}或{{Spacetelescope.org}}。 SOHO (ESA & NASA)聯合項目的探測器所創作的所有內容受到著作權保護，並且進行非教育性質的商業應用需要授權。[2] 每日一天文圖（APOD）網站的特色圖片可能受到著作權保護。[3]

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)