黑洞到底是什么【时间简史 A Brief History of Time :04A】

Questions:

1.How is a star formed?
2.When will stars remain stable?
3.What is a black hole?

To understand how a black hole might be formed, we first need an understanding of the life cycle of a star. A star is formed when a large amount of gas (mostly hydrogen) starts to collapse in on itself due to its gravitational attractions.As it contracts, the atoms of the gas collide with each other more and more frequently and at greater and greater speeds-the gas heats up. Eventually, the gas will be so hot that when the hydrogen atoms collide they no longer bounce off each other, but instead coalesce to form helium. The heat released in this reaction, which is like a controlled hydrogen bomb explosion, is what makes the star shine. This additional heat also increases the pressure of the gas until it is sufficient to balance the gravitational attraction, and the gas stops contracting. It is a bit like a balloon- there is a balance between the pressure of the air inside, which is trying to make the balloon expand, and the tension in the rubber, which is trying to make the balloon smaller. Stars will remain stable like this for a long time, with heat from the nuclear reactions balancing the gravitational attraction. Eventually, however, the star will runout of its hydrogen and other nuclear fuels. Paradoxically, the more fuel a star starts off with, the sooner it runs out. This is because the more massive the star is, the hotter it needs to be to balance its gravitational attraction. And the hotter it is, the faster it will use up its fuel. Our sun has probably got enough fuel for another five thousand million years or so, but more massive stars can use up their fuel in as little as one hundred million years, much less than the age of the universe. When a star runs out of fuel, it starts to cool off and so to contract. What might happen to it then was first understood only at the end of the 1920s.

The gravitational field of the star changes the paths of light rays in space-time from what they would have been had the star not been present. The light cones, which indicate the paths followed in space and time by flashes of light emitted from their tips, are bent slightly inward near the surface of the star. This can be seen in the bending of light from distant stars observed during an eclipse of the sun. As the star contracts, the gravitational field at its surface gets stronger and the light cones get bent inward more. This makes it more difficult for light from the star to escape, and then the light appears dimmer and redder to an observer at a distance. Eventually, when the star has shrunk to a certain critical radius, the gravitational field at the surface becomes so strong that the light cones are bent inward so much that light can no longer escape. According to the theory of relativity, nothing can travel faster than light. Thus if light cannot escape, neither can anything else; everything is dragged back by the gravitational field. So one has a set of events, a region of space-time, from which it is not possible to escape to reach a distant observer. This region is what we now call a black hole. Its boundary is called the event horizon and it coincides with the paths of light rays that just fail to escape from the black hole.

KeyWords & Phrases
1)hydrogen n. <化>氢
2) collapse v. 崩溃; 倒塌
3) gravitational attraction 万有引力
4) collide v. 碰撞; 相撞
5) atom n. 原子; 原子能
6) bounce off 弹开
7) coalesce v. 联合，合并；to come together to form one larger group
8) helium <化>氦
9) contract （使）收缩，缩小
e.g. Glass contracts as it cools. 玻璃遇冷收缩。
10) rubber n. 橡胶; 橡皮
11) paradoxically adv. 矛盾的是；似矛盾而（可能） 正确的
12) light cone 锥形[散开]光束
13) tip n. 末端，尖端；小费；小窍门
14) eclipse n.（日、月）食
15) dim adj. 暗淡的，昏暗的
16) shrink v. 收缩，皱缩
17) boundary n. 边界
18) coincide v. 与…一致，相符

根据今天课程讲解翻译以下句子段落.

Paradoxically, the more fuel a star starts off with, the sooner it runs out. This is because the more massive the star is, the hotter it needs to be to balance its gravitational attraction. And the hotter it is, the faster it will use up its fuel.

矛盾的是，一个恒星开始时的燃料越多，它耗尽地越快。这是因为，恒星质量越大，它为平衡引力所需要的温度就越高。而温度越高，它耗尽燃料的速度就越快。