simulations of the milky way galaxy predict that dozens of small satellite galaxies should be surrounding it in all directions. yet when astronomers observe the night sky, they find that satellite galaxies form a single plane–one that stretches roughly perpendicular to the plane formed by the milky way’s spiral arms. studies of the nearby andromeda galaxy reveal that its satellite galaxies also form a plane. computer simulations suggest that large structures of dark matter play a crucial role.
dark matter’s pervasiveness has solidified belief in its existence. in fact, most cosmologists believe dark matter constitutes around eighty percent of all matter, outweighing normal atoms by around five to one. but what is dark matter? can we even think of it as matter at all, or is it a misnomer?
the truth is, no one knows. we know how it works, and how it influences the visible universe. the closest anyone has come to understanding what dark matter is believes it’s made of gravity. that gravity then has an effect on the visible material around it.