What is the physical structure defining the boundary around a black hole from which escape is impossible?
Answer
The event horizon
The event horizon is defined as the boundary in spacetime surrounding a black hole beyond which the gravitational pull is so strong that nothing, including light, can escape its influence.

#Videos
How the Collapse of Stars Produces Elements | BBC Earth Science
Related Questions
What imbalance immediately triggers the catastrophic implosion known as gravitational collapse in a dying star?In stars up to about eight times the Sun's mass, what physical mechanism usually halts the initial gravitational collapse to form a stable remnant?What is the term for the process where intense core pressure forces electrons into protons, creating neutrons and releasing neutrinos?Which threshold determines whether a collapsing core stabilizes as a neutron star or continues collapsing toward a black hole?If a collapsing core remnant's mass is between approximately 1.4 and 3 solar masses, what object is formed?What characteristic allows astronomers to detect rapidly spinning neutron stars as pulsars?What phenomenon is responsible for dispersing heavy elements across the interstellar medium following a core-collapse supernova?What is the physical structure defining the boundary around a black hole from which escape is impossible?What causes the material in a neutron star to achieve such incredible density?Besides the visible supernova blast, what other type of disturbance created by the collapse can be directly detected on Earth using instruments like LIGO?