Ferromagnetic fluid is great stuff, but it actually has more practical uses than simply dancing around whenever a magnet gets near. Researchers at Université Laval in Quebec are looking to use the fluid to replace mercury in liquid mirrors, in effect creating a tiltable, highly reflective surface ideal for use in telescopes.
Current liquid mirror telescopes use a bowl of mercury that is spun at high speed until the mercury spreads out to a thin layer. The result is great for telescopes, as the surface of the mercury is very reflective, but it cannot be tilted and as such only provides a view straight up. Denis Brousseau's team have suggested using ferromagnetic nanoparticles suspended in oil, which would be manipulated via an array of tiny electromagnets to counteract any optical flaws caused by the atmosphere.
Using a combination of thicker oils and clever deformation, such mirrors could be tilted far more than those which are mercury-based. The research describes not only the methodology for creating ferrofluid mirrors but the ways in which they could be controlled; however it is all theoretical and proof-of-concept at present.