How many things can you see in the night sky? A lot! On a clear night you might see the Moon, some planets, and thousands of stars.
But scientists believe there are some things in the sky that we will never see. We won’t see them with the biggest telescope (望远镜) in the world, on the clearest night of the year. That’s because they are invisible (看不见的). They’re the mysterious dead stars called black holes.
You might find it hard to imagine that stars die. After all, our Sun is a star. Year after year we see up in the sky, burning brightly, giving us heat and light. The Sun certainly doesn’t seem to be getting old or weak. But stars do burn out and die after billions of years.
As a star’s gases burn, they give off light and heat. But when the gases run out, the star stops burning and begins to die.
As the star cools, the outer parts of the star pull in toward the center. The star is squashed (挤压) into a smaller and smaller ball. If the star was very small, the star ends up as a cold, dark ball. If the star was very big, it keeps being squashed inward until it’s packed together tighter (紧的) than anything in the universe.
Imagine if the Earth collapsed until it was the size of a tiny marble (玻璃球). That’s how tightly this dead star, a black hole, is packed. What pulls the star in toward its center with such power? It is the same force that pulls you down when you jump – the force call gravity. A black hole is so tightly packed that its gravity absorbs everything – even light. The light from a black hole can never come back to your eyes. That’s why you see nothing but blackness.
So the next time you look up at the night sky, remember: there’s more in the sky than meets the eye! Scattered (散落) in the silent darkness are black holes – the great mystery of space.
【小题1】What might happen after a star dies?| A．The star might become a black hole. | B．The Earth might be hit by the star. |
| C．The sky might become much darker. | D．The gravity might totally disappear. |
| A．Its gases run out. | B．It hits other stars. |
| C．It gets too hot. | D．Its light fades away. |
| A．Rolled. | B．Ran. | C．Fell inward. | D．Spread out. |
| A．Most black holes are too far away. | B．We don’t have a powerful enough telescope. |
| C．Black holes can travel as fast as light. | D．Light can not escape a black hole’s gravity. |
