What does the term "event horizon" relate to in Tyson's discussion of black holes?

The term "event horizon" in Tyson's discussion of black holes specifically refers to the boundary beyond which no information can escape the gravitational pull of the black hole. This means that once something crosses this critical threshold, it cannot send signals or matter back to the outside universe; it effectively becomes invisible to any observers who are not inside the event horizon.

This concept is fundamental to understanding black holes, as it signifies the limits of our observational capacities when it comes to these mysterious cosmic phenomena. The event horizon marks the point where the escape velocity exceeds the speed of light, making it impossible for anything, including light itself, to escape once crossing this boundary.

The other options do not adequately capture the essence of the event horizon. The gravitational forces exerted by nearby stars relate more to the dynamics of star interactions rather than the specific characteristics of a black hole's event horizon. The observable universe's distance from Earth pertains to the limits of what we can see in the universe but does not connect directly to the nature of black holes. Similarly, while the idea of a "point of no return" can be associated with the event horizon, it does not state the unique aspect of the inability to escape or communicate beyond it, which is key to its definition.