Complex sentence: Born in supernova explosions, these bodies are only ~ 12-13 kilometers by radius and spin around as rapidly as 716 times a second, or approximately 43,000 revolutions per minute.
Split into simpler sentences: Born in supernova explosions, these bodies are only ~ 12-13 kilometers by radius. They spin around as rapidly as 716 times a second, or approximately 43,000 revolutions per minute.