# event horizon

CEFR C2 · Noun

Source: https://englishreference.com/word/event-horizon
Updated: 2026-04-24

## Definition

the imaginary line around a black hole that prevents anything from getting out. Once something crosses this point, it can never come back because the gravity is too strong.

For teachers: the boundary surrounding a black hole beyond which the escape velocity exceeds the speed of light. Represents a point of no return where gravitational pull prevents all matter and electromagnetic radiation from escaping.

## Examples

- Nothing can escape once it passes the event horizon.
- The probe collected valuable data until it reached the event horizon and signals were lost.
- In general relativity, the event horizon serves as a threshold where the gravitational field becomes so intense that even light is unable to traverse the path back to the external universe.

## Usage notes

- Typically used with the definite article 'the' when referring to a specific black hole.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.