Strangelet

There is a hypothetical particle called a strangelet that we might find in the cores of neutron stars. If they do exist, these might be the most stable matter in existence and therefore might be the most dangerous substance in the universe. If one were to strike earth (or any object in the universe), it could turn that matter into further strangelets creating a chain reaction that would result in the Earth being turned into one big strangelet. They might actually be the dark matter that we suspect holds galaxies together.