If there are supermassive black holes at the center of most galaxies, why are there not massive stars at the center of galaxies as well?
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Along with previous answers:
The larger a star is, the faster it will burn through its fuel. Basically the bigger it is, the shorter it lives.
Our sun is a relatively small star compared to some of the giants. It will “live” for approx. 10 billions years. Current age is approx 4.5 billion years.
The universe is currently estimated to be approx. 13.8 billion years, depending on the study you look at.
Super massive stars only live for tens or hundreds of millions of years. If they are large enough, the end process of their life will result in a supernova that leaves behind a black hole. So even if the core area started with a cluster of large stars, they would have quickly (astronomically speaking) burned out and created black holes.
Stars can only get so big.
The more mass a star has, the more energy it generates. The more energy it generates, the more powerful the solar wind and photon pressure it emits.
The largest stars several hundred times the mass of the sun emit so much energy that they start shredding themselves. The intense power from the core peels the outer layers away like a cosmic onion and the star can grow no larger.
How supermassive black holes millions of times more massive than that formed so quickly (or at all) is still a bit of a mystery.
There’s a limit to how massive a star can be before the thermal pressure from inside succumbs to the gravitational pull of its mass. And that limit is far below of what’s needed to hold a whole galaxy together.
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