Unit 4 Astronomy: the science of stars教案

如今，霍金終于改變了觀點，在當天召開的學術研討會上，霍金說，根據他的最新發現，黑洞并非只是吞噬物質。除了會在星系形成的過程中扮演重要角色外，在經過一段相當漫長的時間后，黑洞也會把一些曾被它吸入的物質信息向外界釋放出來。
霍金的最新闡述被不少人稱為黑洞理論的一個重要逆轉。美國加州理工學院的理論物理學家約翰•普雷斯基就是其中之一。20多年前，霍金提出黑洞輻射理論時，普雷斯基就一直堅持物質信息不會完全消失，當時兩人還因此打賭。所以，在當天結束演講后，霍金將一本百科全書贈予普雷斯基，作為打賭輸了的代價，而普雷斯基則獲得了全場的熱烈掌聲。
black holes
(1) what is a black hole? well, it's difficult to answer this question, since the terms we would normally use to describe a scientific phenomenon are inadequate here. astronomers and scientists think that a black hole is a region of space (not a thing ) into which matter has fallen and from which nothing can escape---- not even light. so we can't see a black hole. a black hole experts a strong gravitational pull and yet it has no matter. it is only space ---- or so we think . how can this happen?
(2) the theory is that some stars explode when their density increases to a particular point; they collapse and sometimes a supernova occurs. form earth , a supernova looks like a very bright light in the sky which shines even in the daytime. supernovae were reported by astronomers in the seventeenth and eighteenth centuries. some people think that the star of bethlehem could have been a supernova. the collapse of a star may produce a white dwarf or a neutron star--- a star , whose matter is so dense that it continually shrinks by the force of its own gravity. but if the star is very large (much bigger than our sun) this process of shrinking may be so intense that a black hole results. imagine the earth reduced to the size of a marble, but still having the same mass and a stronger gravitational pull, and you have some idea of the force of a black hole. any matter near the black hole is sucked in. it is impossible to say what happens inside a black hole. scientists have called the boundary area around the hole the " event horizon." we know nothing about events which happen once objects pass this boundary. but in theory, matter must behave very differently inside the hole.
(3) for example , if a man fell into a black hole, he would think that he reached the center of it very quickly. however an observer at the event horizon would think that the man never reached the center at all. our space and time laws don't seem to apply to objects in the area of a black hole. einstein's relativity theory is the only one which can explain such phenomena , so that there is no " absolute" time and space depend on the position of the observer. they are relative. we do not yet fully understand the implications of the relativity theory; but it is interesting that einstein's theory provided a basis for the idea of black holes before astronomers started to find some evidence for their existence. it is only recently that astronomers have begun specific research into black holes. in august 1977, a satellite was launched to gather data about the 10 million black holes which are thought t be in the milky way. and astronomers are planning a new observatory to study the individual exploding stars believed to be black holes.