Roughly 80 percent of the mass of the universe appears to be dark matter: an invisible material that seems to interact with ordinary matter only through gravity, without emitting light or energy. Scientists cannot detect dark matter directly and don't yet know what it's made of, but they track its influence based on the motions of stars and galaxies. The presence of dark matter is necessary to explain the universe's current structure.
For centuries, humans have wondered, Are we alone? and What is the universe made of? Scientists will tackle these exact questions in two documentaries, part of the new, six-episode PBS series "Nova Wonders."
White holes, which are theoretically the exact opposites of black holes, could constitute a major portion of the mysterious dark matter that's thought to make up most of the matter in the universe, a new study finds.
New, more accurate measurements of a group of colliding galaxies appear to indicate that dark matter interacts with itself and ordinary matter only via gravity, reversing conclusions scientists had drawn from observations three years earlier.