Black hole (phenomenon)

A black hole is an astronomical feature that occurs when a massive star collapses into a extremely small singularity so dense than not even light can escape its gravatational field.

Transformers have encountered black holes on a number of occasions and they have frequently been show to function as portals between alternate universe:

A Quintesson ship with captured Autobots and Decepticons aboard passed through one to a universe where the color spectrum was reversed.

A specially outfitted Powermaster Optimus Prime journeyed into one to discover nucleon.

The bounty hunter Axer traveled through one from the Generation 1 continuity to the Robots in Disguise continuity.

In the Unicron Trilogy, Unicron's destruction created an especially large black hole which threatened to destroy the universe but it was stopped by Primus.

From Teletraan I: The Transformers Wiki, a Wikia wiki.