水母星雲
The Medusa Nebula
這蜿蜒而又纏繞的燈絲狀物質是由熾熱氣體形成的，該形狀也已經暗示了該星云通俗的稱呼，那就是水母星雲。水母星雲也被稱為 Abell21 ，是雙子座內一個較老的行星狀星雲 ，距離我們大約 1500 光年。就像它那富有神話色彩的名字一樣，星雲還有一段富有戲劇性的形成過程。這個行星狀星雲所處的階段是類似太陽的低質量恆星演變的最後階段，也就是它將從紅巨星轉變成白矮星，擺脫外層氣體的階段。從熾熱恆星放射出的紫外線激發了星雲，並使它發光發熱。在這張清晰彩色影像中，可以看到水母星雲演變過程中熾熱的中央星，同時在整個明亮新月形的上方還有一顆較小的藍色恆星。還可以清晰地看到較暗的燈絲狀物質向明亮新月區域的上方和左側擴散 據估計水母星雲大小約 4 光年多。
Braided, serpentine filaments of glowing gas suggest this nebula’s popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula some 1,500 light-years away in the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun, as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. The Medusa’s transforming hot central star is visible in the detailed color image as the small blue star within the upper half of the overall bright crescent shape. Fainter filaments clearly extend above and to the left of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.
