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 sparkling stars. You can see even more with a telescope.
But scientists believe there are some things in the sky that we will never see. We won’t see them with the biggest telescope in the world, on the clearest night of the year. That’s because they’re invisible. They’re the mysterious dead stars called black holes.
As a star’s gases burn, they give off light and heat. But when the gas runs out, the star stops burning and begins to die.
As the star cools, the outer layers of the star pull in toward the center. The star squashes (挤压) into a smaller and smaller ball. If the star was very small, the star ends up as a cold, dark ball called a black dwarf. If the star was very big, it keeps squashing inward until it’s packed together tighter than anything in the universe.
Imagine if the E
A. Because most black holes are so far away.
B. Because the gravity of a black hole is so strong that it sucks the light inward.
C. Because as the star’s gases burn, it stops giving off heat and light.
D. Because as a star cools, its outer layers pull in toward its center.
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