What was that contraption in the film 'The Arrival', a portable black hole?

Question

Any thoughts on how it was supposed to work, and be selective and timed etc?

Yes - at one point it seemed as if there was something looking out of it.

Answer 1

More like a worm hole. A black hole would add the imploded mass to its own and just keep growing until the Earth was swallowed up, and then just sit there. A worm hole transports matter to another part of the universe, or another universe altogether. Worm holes are also inherently unstable and vanish after a period of time (like the ball thing). The aliens just figured out how to make a worm hole last a minute or so instead of a Planck time.