The largest, most massive, densest, black hole in our local universe is our local universe itself. Continuously accelerate in it long enough and you will warp its vertical flexible Abyss of space-time, stars, galaxies, dust, eventually simply vacuum debris, in on you, and possibly pop out of its horizon and jet into some other universe's stars, galaxies, and so on, being surprised you've hardly begun to accelerate. Black hole type mass density in one dimension is a universe of vacuum (possibly negative in speed (decelerating to possibly (-)300,000kps relative to you sitting at a stop sign on Earth), possibly loaded with negative energy) in another dimension. There are already articles out there talking, and experiments being performed, drawing some slight energy from the nothing of a void or vacuum.