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Astronomers at Kitt Peak National Observatory near Tucson. Arizona have discovered what they claim are the largest structures yet observved in the universe. The structures are glowing blue arcs of light nearly 2 million trillion miles in lenght. The discoverers of these arcs think they are actually optical illusions created by light that has been bent due to the immerse gravitacional pull of a massive galaxy. The arcs are probably formed when the light from a distant galaxy is bent by the gravitational pull of another, less distant, interviewing galaxy. Even though such light-bending galaxies contain billions of stars, they still do not contain enough visible stars which alone could exert the pull needed to bend light in such a way. Therefore, it is theorized that there must be huge amounts of invisible or "dark" matter within these galaxies. Furthermore, astronomers say that there might be enough dark matter in the universe to supply enough gravity to slow the expansion of the universe and then make it eventually colapse.

1) This passage mainly deals with:

a) how the universe expands
b) what effects gravitational pull has on galaxies
c) what "dark" matter is
d) how arcs in space are created.



2) According to the passage, galaxies can bend light through their:

a) extreme distance
b) gravitational pull
c) stars
d)arcs