Phys.org
Singularity
The point where our description of gravity stops producing meaningful answers.
General relativity says the matter inside a black hole collapses to a point of infinite density. Infinity in a theory usually signals that the theory has been pushed past its range rather than that nature contains an infinity, and the singularity is the standard example: gravity is strong and the scale is tiny, which is exactly the regime where quantum mechanics and relativity are known to disagree. What is actually there requires a theory of quantum gravity that nobody has.
Where it has come up lately
Related terms
Event horizon
The boundary around a black hole past which nothing gets out — not a surface, but a point of no return.
Accretion disc
The flat, ferociously hot spiral of matter falling onto a compact object.
Schwarzschild radius
How small you would have to squeeze something to make it a black hole.
Supermassive black hole
Millions to billions of solar masses, one at the centre of essentially every large galaxy.
Questions
What is Singularity?
The point where our description of gravity stops producing meaningful answers.
Why does it matter?
Infinity in a theory usually signals that the theory has been pushed past its range rather than that nature contains an infinity, and the singularity is the standard example: gravity is strong and the scale is tiny, which is exactly the regime where quantum mechanics and relativity are known to disagree. What is actually there requires a theory of quantum gravity that nobody has.