Hang Yu

A black hole can torment a star for years, rather than rip it apart immediately. Tidal forces are when the hole's gravity stretches the star: the near side is pulled harder than the far side. Usually, getting too close rips the star apart instantly — that's a tidal disruption event.

Two neutron stars are two city-sized spheres with the mass of the Sun. As they spiral together, tidal forces stretch each one, as if a giant hand were squeezing and twisting a rugby ball. The star begins to oscillate — density waves run through it, like ripples on water from a thrown stone.