Black hole search

A connected graph contains one black hole: a node that destroys any agent arriving there, leaving no trace. All other nodes are safe. Agents start at a safe node \(s\) (the home base) and must determine the location of the black hole; at least one agent must survive and know it. The primary measure is the team size (number of agents needed); the secondary measure is the cost (total number of moves, a move being one traversal of one edge) or, for synchronous agents, the time. In most settings the black hole is present from the start; an eventually emerging black hole appears at an unknown time during the execution, and time is then counted from its appearance. Some papers also start the agents scattered, at distinct safe nodes; those results are recorded in the notes, because every catalogued variant starts at a home base.

Measures: Agents, number of agents needed (team size); Cost, total moves (asynchronous) or rounds (synchronous).