The best replacement for black hole is black hole.

The best alternatives to black hole are rated as following:
★★★★★  black hole
★★★★★  neutron star
★★★★★  wormhole
★★★★  white hole
★★★  star
★★★  dark matter
★★★  supernova
★★★  quasar
★★  sun
★★  white dwarf
★★  big bang
★  singularity
★  supermassive black hole
  worm hole
  archon
  gamma ray burst
  magnetar
  vortex

Your alternative for black hole is not listed? Suggest!
Speaking about black hole, one probably shouldn't forget about galaxy.

Other search terms related to black hole and their ratings are:
★★★★★ galaxy
★★★★★ accretion disk
You have in mind a companion for black hole and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of black hole in all years. Click on graph for more.
black hole
black hole
neutron star