(in which a lapsed metalhead seeks the heaviest metal song ever - recommendations are welcome)
Sea Bastard are a doom band from Brighton, UK. So sayeth their Bandcamp profile and I see no reason to dispute any of this. Astral Rebirth appears on a split release from Keeper and Sea Bastard that appeared a few years back. It's the first bit of Sea Bastard's work I heard and it is a truly majestic bit of heavy.
In some of these features I've mentioned that the song discussed is not really a candidate for the title of heaviest ever but is under consideration because it is worthy of note. Not so for Astral Rebirth. It is indeed one of the heaviest things I've heard. How it will stack up when this is all over I can't say yet. But it's definitely a contender.
It's a minimalist piece of work (I guess) and not everyone can pull off this sort of thing but Sea Bastard accomplishes it with admirable skill. The first half of the piece is given over to a lumbering riff, of sorts, that the band hammers away at for about eight or nine minutes. Next up, a noisy break that lasts for a few more minutes. It's pretty impressive stuff up to this point, but then things really get rolling with a bludgeoning riff that couldn't be much heavier, by my reckoning. A bit of clunking and slamming closes things out and if you're like me, your first impulse is to start it all over again.