the black celestial arc shows him absorbing the universe, then destroying it with his UN.
In annihilation, galactus was going to be the means with which annihilus would destroy not only the 616 marvel unviverse, but also the negative zone as well. annihilus simply planned to blow up galactus from within, and the resulting blast would destroy not one, but two universes. moondragon and thanos confirmed this to be completely possible.
Gender: Male Location: Following the Source of Light.
True. Galactus is capable of destruction on a universal level. I don't know if this makes him a match for AM, but give Galan the Ultimate Nullifier (which has been stated to be a part of him and not just a random weapon) and all bets are off.
But this was only after Galactus was turned into a "slave" by the Black Celestial, and his hunger made limitless.
It's not just like Galactus can go out and devour an entire Universe whenever he pleases, or at least he's never shown that ability completely under his own power.
That's true. But we now venture into a grey area, because by the very nature of Galactus' character, he would never have any cause to devour the entire universe. Therefore, he would never be depicted as doing it with his own will, as it is not in his nature.
Sort of like when he gathered the infinity gems. He didn't do it for the lust of power (Thanos), but simply to assuage his hunger. Black celestial arc shows that given the proper motivation (his insatiable hunger) Galactus can and does devour the entire universe.
We know that Galactus is capable of doing it with external manipulation of his hunger. but it's only his hunger that's manipulated, not his inherent abilties.
so in the end, we know galactus is capable of doing it in some form, yes. is he capable of doing it on his own, debatable. he has no reason to, no just cause. he would never do it on his own. but the fact remains that he can do it, in some capacity.
IMO all the Black Celestial arch shows us is Galactus's potential, under optimal conditions.
By this I mean that Galactus is capable of absorbing a Universe.
But,
He has never shown the ability to do anything close to this, without external manipulation of some sort.
Thus, we really cannot say that it's possible for him do accomplish such a feat, whenever he pleases. (Unless of course it's specified that the version of Galactus to be used, is the version from the B/C arch).