Two popular eastern Sydney beaches were closed until further notice after the appearance of “mysterious black” balls, local authorities said. Coogee beach, particularly popular with backpackers, was cleared on Tuesday after lifeguards “discovered mysterious, black, ball-shaped debris washed along the length of the beach,” the Randwick city council said in a statement. “At this stage it is unknown what the material is, however, they may be ‘tar balls’ which are formed when oil comes in to contact with debris and water, typically the result of oil spills or seepage,” the statement continued. On …