lime-bloods:

UU: bUt as long as we stand in the centre of this vortex, we may speak as loUdly as we like! no information can escape this dark pocket, so long as i maintain it.

Calliope reveals here in no uncertain terms the true nature of her secret furthest ring hideout; a vortex from which no information can escape* is in fact a black hole. The signature shape of solar material spiraling into a black hole probably gives it away, but this is a pretty clear demonstration of the extent of Calliope’s ability to distort space before her more iconic use of the power in Act 7.

With this in mind, the stage in the middle of the vortex makes it quite a bit more obvious that Calliope’s Act 7 black hole is in fact Homestuck itself.

* Calliope may be dismayed to find that information paradoxically can leave a black hole, and that this is the same principal that leads to angels splitting into two.

Maybe more interestingly, Calliope drops a loaded phrase here; she refers to her secret black hole base using the same terminology Doc Scratch uses to describe the holes in his omniscience;

[…] gaps in my knowledge […] are the pillars of shadow on which my comprehensive vision is built.
Necessary pockets of void meant to effectuate outcomes I’ve foreseen and which will require my influence.
Each dark pocket, in time, will be fille
d.

On the surface level this seems pretty literal; Calliope’s hideout is a “dark pocket” because it was designed to hide her from English’s omnipresence. But Scratch’s declaration that every dark pocket will eventually be filled comes with some implications.

Aranea, too, was aware of these gaps in Scratch’s omniscience, and sought to take advantage of them for her own means:

Loc8ing his so called dark pockets was the only gam8it I had in countering his milktongued dou8lespeak. The expatri8 for indiscerni8le reasons seemed naturally surrounded 8y such a void in the Doctor’s awareness, and so was uniquely fit to inherit the or8.

Again, the surface meaning of this is obvious to us; Scratch can’t see into the obfuscation field surrounding Horuss, so Horuss is a good candidate to keep things hidden from him. But Aranea seems to have a key detail missing from her own understanding; the dark pockets are not Scratch’s weaknesses. They are “meant to effectuate outcomes [he has] foreseen”. Horuss was “uniquely fit to inherit the or8” not because he would hide it from Scratch, but because he was a dark pocket that needed to be filled with English’s seed.

Spades Slick is similarly tasked with delivering a piece of English paraphernalia into a dark pocket (this one provided by Roxy rather than a Zahhak); suggesting, perhaps, that the filling of the pockets in English’s great game of pool is in fact the delivery of his various pieces to him through black holes - such as the one that acts as the actual “pocket” in the center of his session - ala Black Hole Theory?