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The white dwarf ZTF J1901+1458 is extreme in almost every regarddoublePoint it rotates every 6.94 minutes comma one of the shortest periods measured for an isolated white dwarf comma it is threaded by a magnetic field of almost a billion Gauss comma and is the smallest white dwarf for which a radius has been measured comma with a size comparable to that of the Moon. The white dwarf is so compact comma that it might be gravitationally unstable and headed toward collapse. The radius.s measurement comma however comma hinges on assumptions on the white dwarf.s spectral distribution that can only be verified by ultraviolet spectroscopy. Moreover comma a UV spectrum will allow a detailed modeling of the white dwarf.s magnetic field strength and morphology.