That is what I have wondered ever since I first heard of the ‘big bang’. It had to be a humongously large planet; if it were a sun, everything would have been burned up. But, if it were a planet, what provided the light, heat, etc.?
Also, why are all the planets, moons and stars spherical? Asteroids and commets aren’t.
It says way more about all this than I ever could and far more coherently.
And, on that note, incredibly, it’s time for me to go to church!
Not large, but massive. The notion of time didn't exist before the big bang, because there was nothing. Not even space. That's hard to wrap your brain around (no space), but that's what the physics says.
The bang itself was so hot that matter could not exist (energy has mass, so there was a massive amount of energy, and it was very dense, not spread out). at some point after the bang, things cooled down enough that matter could exist.
-- Also, why are all the planets, moons and stars spherical? Asteroids and commets aren't. --
Generally, it's a function of their size. More massive objects, and more "fluid" objects will appear closer to spherical, in part because the deviations from spherical are a small fraction in a large object. A 30,000 foot mountain on a 8,000 mile diameter sphere doesn't much change the impression of spherical. That same 30,000 foot difference in elevation would be big on a 20 mile diameter object - and as the 20 mile diameter object has very weak gravity, not much will or can operate to erode the high spot down to a sphere.
I think it's a moon of Mars that shows a big deviation from spherical, on account of an asteroid strike.