英语听力:自然百科 穿越银河系的旅行 Through Milky Way—9(在线收听

 Like nebulae which spawn stars, it is made of gas and dust. But that's where most similarities end. For Alex Filippenko, it represents an intriguing industrial zone within our galaxy where the elements from which our world is made or manufactured. 

 
What about more iron. Oh,
 
The Crab Nebula is a fascinating object. We see/ very rapidly expanding gases. The Crab may appear static, but its gases are racing out from its center at over 3 million miles an hour, blasted out by a phenomenally powerful event in the past. 
 
What could cause such violence?
 
When we examine the gases of the Crab Nebula which are expanding outward, and we extrapolate that expansion backward in time, we find that all the gases were at a common point about 1000 years ago. 
 
A thousand years ago on earth, there were civilizations watching the heavens. In 1054 AD, Chinese manuscripts tell of the sudden arrival of a brilliant new star which are brighter than any other star. So brightly, it was visible during the day. Then it mysteriously disappeared. 
 
Today the Crab Nebula appears in exactly the same part of the sky where the Chinese observed their brilliant star. What they witnessed was the moment the Crab was born. The Crab Nebula was produced by the colossal titanic explosion of the star at the end of its life. It is a supernova remnant.
 
 
The spiral arms of our Milky Way elated with these colorful remnants, tombstones of stars that died violently in cataclysmic explosions astronomers call supernovae.
  原文地址:http://www.tingroom.com/lesson/zrbaike/2011/260152.html