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Most scientists ag"的相关试题:
[单项选择] Black Holes
Most scientists agree that black holes exist but are nearly impossible to locate.A black hole in the universe is not a solid object,like a planet,but it is shaped like a sphere (球体).Astronomers(天文学家)think that at the center of a black hole there is a single point in space with infinite(无限的)density(稠密).This single point is called a singularity (奇点).If the singularity theory is correct,it means that when a massive star collapses,all the material in it disappears into the singularity.The center of a black hole would not really be a hole at all,but an infinitely dense point.Anything that crosses the black hole is pulled in by its great gravity.
Although black holes do exist,they are difficult to observe.These are the reasons.
● No light or anything else comes out of black holes.As a result,they are invisible to a telescope.
● In astronomical terms,black holes are truly.For example,a black hole formed by the collapse of a giant star would have an event horizon(视
A. Right
B. Wrong
C. Not mentioned
[单项选择]Black Holes
1. Black holes can be best described as a sort of vacuum, sucking up everything in space. Scientists have discovered that black holes come from an explosion of huge stars. Stars that are near death can no longer burn due to loss of fuel, and because its temperature can no longer control the gravitational (重力的) force, hydrogen ends up putting pressure onto the star’s surface until it suddenly explodes then collapses.
2. Black holes come from stars that are made of hydrogen, other gases and a few metals. When these explode it can turn into a stellar-mass (恒星质量) black hole, which can only occur if the star is large enough (should be bigger than the sun) for the explosion to break it into pieces, and the gravity starts to compact every piece into the tiniest particle. Try to see and compare: if a star that’s ten times the size of the sun ends up being a black hole that’s no longer than 70 kilometers, then the Earth would become a black hole that’s only a fraction of an inch!