|Astronomers have discovered a galaxy as big as the Milky Way that consists almost entirely of dark matter, a mysterious and invisible substance that scientists have been trying to figure out for decades. Only one-hundredth of one percent of the galaxy is ordinary, visible|
matter like stars and planets. The other 99.99 percent of the stuff in this galaxy can’t be seen.
No one really knows what dark matter is made of, but scientists believe it exists because they can see the effects of its gravity on other things in space. Whatever it may be, about 80 percent of the mass in the universe is dark matter. …