Circumstellar matter ; solar system : formation ; planetary systems : protoplanetary disks ; stars : pre-main sequence .

太阳系形成;原行星盘;环星物质;前主序星。

Circumstellar matter , solar system : formation , planetary systems : protoplanetary disks , stars : pre-main sequence .

太阳系形成,原行星盘,环星物质,前主序星。

But the larger envelope of circumstellar dust extends some 60 billion kilometers into space , equivalent to about 400 times the earth-sun distance .

但是拱星四周星尘更大的外壳可以向宇宙延伸600多亿公里，相当于地球到太阳距离的400倍。

Another expectation , which hubble overturned , was that the circumstellar disks would be deeply embedded within their parent clouds and would therefore be impossible to see .

另外有一个被哈伯推翻的猜测，是因为环绕恒星的气盘深藏在其母云气之中，所以无从窥其究竟。

A common character in these two group stars is presence of infrared excess , which is not attributed to the central star , but its circumstellar material .

这两类星都有一个共同的特性--具有过量的红外辐射，或称为红外超。红外超不是由中心恒星产生，而是由星周物质产生。