Method to weigh galaxy clusters could help astronomers understand mysterious `dark matter` structures
(PHYSorg.com Space & Earth)

The furthest galaxy ever observed is so far away that the starlight we now detect was emitted less than 500m years after the Big Bang. It has taken about 13 billion years to reach us. But there`s a lot of things about a galaxy that we can`t see. For example, we think galaxies are immersed within gigantic `halos` of an invisible substance dubbed dark matter. Scientists don`t actually know what dark matter is, but they know it exists because it has a gravitational pull on surrounding matter.