When the oppositely charged energon from Unicron's body and detached head came into contact with each other, the cataclysmic result was a rift which sundered the very fabric of existence. Glowing bright yellow sometimes and shimmering deep black-purple at others, the rift constantly sucked in a stream of space debris, making it hazardous for anyone caught in its grip. On the other side, a peaceful realm of space existed, where, for a time, Alpha Q was able to nurture his precious planets.
It may or may not have had a black hole at its heart. It may or may not be a black hole.