The ability to summon a black hole, is an ultimate power of magic. Though most spells are formed by aligning stars, rather than regions of space connected by dimensional doors.
So, it has another use.
Really, these are shields of gravitational weaponry created, to block the subspace passages between dimensions. They exist for that logical reason, both inside the mind of the summoner, (which drives most with the talent for magic insane), and also bordering the abyss; adjusting there location in subspace automatically.
A singularity, is like a storm, except it makes use of a forbidden rune, unlike other rune types.
The duration, is also included in a runic form as elements of measurable energy, by the several small runes, (that not even a master can read accurately, in the margins of the cosmic cliff notes.). Forming a rune, it would be written, where nature had intended a storm.
A basic charm connects energy elements like previous storms, the same way as aligned stars. Then align the correct chosen rune, for the energy element, and divine intent for its use. (smite).
The strength or intent of its use, is based on the runic form, made up of smaller runes, that make up larger runes. This indicates an energy type. The same rune can be written multiple ways.
To get a workable spell, first you select a star type, Then you connect to stars, with the same energy type. What you get, is a rune path to direct energy, that can effect or direct, the actions of living things.
So that is how basic charms are formed to include void elements.