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black-holes × 201science-based × 68
physics × 37
space × 30
hard-science × 24
gravity × 24
internal-consistency × 23
science-fiction × 18
planets × 16
astrophysics × 11
technology × 10
orbital-mechanics × 10
energy × 10
space-travel × 9
astronomy × 9
faster-than-light × 9
weapons × 7
spaceships × 7
stars × 7
wormholes × 7
relativity × 6
time-travel × 5
habitability × 5
weapon-mass-destruction × 5
apocalypse × 4