Have you ever looked at the sky and thought about darkness? Is it nothing? Or is there something in the dark? Cosmologists (宇宙学家) try to answer questions about things in space. They even study the darkness in space. They say the universe is about 5 percent “normal” matter—things we can see, like Earth and other planets, and the sun and other stars. But about 70 percent of the universe is something called dark energy.

Cosmologists say the other 25 percent of the universe is dark matter. Dark matter has some weight. It’s heavy so we know it’s there. But we can’t see it, so it is very hard to study something that you can’t see!

One possible kind of dark matter is a brown dwarf (褐矮星). A brown dwarf is too big to be a planet and too small to be a star. Brown dwarfs are colder than stars, and they don’t give off light that people can see. Cosmologists found them by using a telescope that finds heat. They found the first brown dwarf in 1995.

Cosmologists know a lot about one kind of dark matter—black holes. In 1783, an English astronomer, John Michell, guessed that there were black holes. But cosmologists didn’t find any black holes until 188 years later. Since then, they’ve found many black holes in space.

It’s very dark with much gravity (引力) in a black hole. There is so much gravity in a black hole that nothing can get out, not even light. This is why we can’t see them. Cosmologists find black holes by looking at things around them.

For example, stars and gases near a black hole move very fast.

Things in space can fall into a black hole, and when they do, they can never get out. But don’t worry—Earth will never fall into a black hole because there is not one close enough.

【小题1】When did cosmologists first find black holes?

A．In 1783.

B．In 1971.

C．In 1995.

D．In 1595.

【小题2】What can we know about brown dwarfs?

A．They are as big as planets or stars.	B．They give off light that people can sec.
C．The first one was found by using a telescope.	D．They are much hotter than stars and planets.

【小题3】What would be the best title for the passage?

A．Black Holes in Space.	B．Dark Energy in Space.
C．Normal Matter in the Universe.	D．Dark Matter in the Universe.

【小题4】What can we infer from the passage?

A．We have known nothing about dark matter so far.

B．Earth could fall into a black hole in several centuries.

C．The earth is too far away from a black hole to fall into it.

D．The biggest black hole is as big as ten billion of our sun.