A planet-hunting NASA spacecraft has detected no sign of moon-size black holes yet in the Milky Way galaxy, limiting the chances that such objects could make up most of the "dark matter" that has mystified scientists for decades.
Dark matter is one of the greatest scientific mysteries known — an invisible substance thought to constitute up five-sixths of all matter in the universe. It remains so mysterious that scientists are still uncertain as to whether dark matter is made of microscopic particles or far larger objects.
The consensus right now is that dark matter consists of a new type of particle, one that interacts very weakly at best with all the known forces of the universe except gravity. As such, dark matter is invisible and mostly intangible, with its presence only detectable via the gravitational pull it exerts.
However, despite research from thousands of scientists relying on the most powerful particle accelerators on Earth and laboratories buried deep underground, no one has yet detected or created any particles that might be dark matter. This led Kim Griest, an astrophysicist at the of California, San Diego, and his colleagues to investigate black holes as potential dark matter candidates.