Ferrofluids were invented in the 1960s by a NASA engineer. These fluids are made up of very small particles of a magnetic material such as iron oxide mixed with a coating agent that keeps the particles from clumping mixed in a watery or oily liquid. Their distinguishing property is that ferrofluids can be moved by magnets and the fluid aligns itself with the magnetic field forming spikes.
In the video below, Dianna Cowern from the YouTube channel Physics Girl, sets out to take slow motion pictures of drops of ferrofluids splashing on a strong magnet just for the fun of it, and ends up modeling the tidal forces that produce epic black hole death due to spaghettification!
Ferrofluids have been employed by artists to create amazing sculptures, but they are also used in many technological applications such as in rotating shaft motors like computer hard drives to form seals, in loudspeakers to remove heat and dampen vibrations, and as contrast agents in magnetic nuclear imaging. Many other potential applications of ferrofluids are being researched.