Black Holes

　　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 exerts a strong gravitational pull and yet it has no matter. It is only space - or so we think. How can this happen?

　　The theory is that some stars explode when their density increases to a particular point; they collapse and sometimes a supernova occurs. From 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 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.

　　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. Einstein claimed that matter and energy are interchangeable, so that there is no "absolute" time and space. There are no constants at all, and measurements of 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 hole. In august 1977, a satellite was launched to gather data about the 10 million black holes which are thought to be in the Milky Way. And astronomers are planning a new observatory to study the individual exploding stars believed to be black holes.

　　The most convincing evidence of black holes comes from research into binary star systems. Binary stars, as their name suggests, are twin stars whose position in space affects each other. In some binary systems, astronomers have shown that there is an invisible companion star, a "partner" to the one which we can see in the sky. Matter from the one which we can see is being pulled towards the companion star.

　　Could this invisible star, which exerts such a great force, be a black hole? Astronomers have evidence of a few other stars too, which might have black holes as companions.

　　The story of black holes is just beginning. Speculations about them are endless. There might be a massive black hole at the center of our galaxy swallowing up stars at a very rapid rate. Mankind may one day meet this fate. On the other hand, scientists have suggested that very advanced technology could one day make use of the energy of black holes for mankind. These speculations sound like science fiction. But the theory of black holes in space is accepted by many serious scientists and astronomers. They show us a world which operates in a totally different way from our own and they question our most basic experience of space and time.

　　黑洞

　　什么是黑洞呢?這個問題很難回答，因為我們通常用來描述一種科學現象的術語用在這里來解釋是不夠的。

　　天文學家和科學家們認為黑洞是個空間區域，物體會掉進去，而沒有物體能從中逃逸出來――即使是光也不能，所以我們看不到黑洞。黑洞產生很強的引力，而它卻沒有物質。它只是空間――或者我們認為是空間。這是怎樣發生的呢?

　　理論是一些星球的密度增長到特定的時刻就會爆炸。它們崩潰時會產生超新星。在地球上看去，超新星就像天空中非常耀眼的燈，即使在白天也能看到其閃光。在17、18世紀，天文學家就有關于超新星的記錄，一些人認為圣誕星可能是一顆超新星。一顆星崩潰可能產生吸引力，你就了解黑洞的力量。黑洞附近任何物質都會被吸進去，根本不可能說出黑洞里面發生了什么。科學家們把這個洞的邊緣區域稱為"事界"。一旦物體經過這個邊界，我們對所發生的事一無所知。

　　但是在理論上，在黑洞里的物質的運動肯定與洞外有很大區別。例如：如果一個人掉進黑洞，他會認為自己很快就達到了其核心，但在"事界"的觀察者則認為這個人根本不會到達黑洞的核心。我們的時空規律看起來不適于黑洞里的物體。愛因斯坦的相對論是唯一可以解釋這種現象的理論。愛因斯坦聲稱物質和能量是可以互相轉化的，因此就沒有絕對的時間和空間，根本不存在永恒，時間和空間的衡量取決于觀測者所在的位置，它們是相對的。我們還沒有完全理解相對論的含義，但有意思的是，在天文學家的著手發現黑洞的存在證據之前，愛因斯坦就提供了黑洞這種想法的基礎。只是近來科學家才開始對黑洞的具體研究。1977年8月，發射了一顆衛星去收集關于被認為是在銀河系的一千萬個黑洞的數據。天文學家正在計劃一個新的天文臺以研究個別的正在爆炸的被相信要變為黑洞的星球。

　　黑洞最有說服力的證據來自對雙星系的研究。雙星，正如它們的名字所表明的，是兩顆在空間位置上互相影響的星球。在一些雙星系里，天文學家已經表示這里有一顆看不到的伴星，即我們可以在天空中看到的一顆星球的伙伴。來自我們的看到的星球的物質正被吸引到伴星去。這顆產生如此巨大力量的看不見的星球會是黑洞嗎?天文學家還有其他一些星球的證據，這些星球可能與黑洞相伴。

　　對黑洞的研究剛剛開始，各種推測會層出不窮。在我們銀河系的中心很可能存在著一個巨大的黑洞正以極快的速度吞食著星球。人類有一天也會面臨被吞食的命運。而科學家提出，有一天高科技利用軒洞的能量為人類服務。這些設想聽起來像科幻小說，但空間中黑洞的理論被許多嚴謹的科學家和天文學家接受。他們向我們展示了一個以完全不同于我們理解的方式運行的世界，并對我們最基本的時空經驗提出了疑問。