Universe Today
Supermassive black hole
Millions to billions of solar masses, one at the centre of essentially every large galaxy.
Sagittarius A* at the centre of the Milky Way holds about four million solar masses, measured by tracking individual stars orbiting it for decades — work that won a Nobel Prize. Most large galaxies have one, and its mass correlates tightly with the galaxy's central bulge, which implies the two grew together. How they got so big so early is unsettled: quasars a billion solar masses exist when the universe was under a billion years old, which is barely enough time.
Where it has come up lately
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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.
Singularity
The point where our description of gravity stops producing meaningful answers.
Schwarzschild radius
How small you would have to squeeze something to make it a black hole.
Questions
What is Supermassive black hole?
Millions to billions of solar masses, one at the centre of essentially every large galaxy.
Why does it matter?
Most large galaxies have one, and its mass correlates tightly with the galaxy's central bulge, which implies the two grew together. How they got so big so early is unsettled: quasars a billion solar masses exist when the universe was under a billion years old, which is barely enough time.