Testing MOND Over a Wide Acceleration Range in X-Ray Ellipticals
  The gravitational fields of two isolated ellipticals, NGC 720 and NGC 1521,
have been recently measured to very large galactic radii (~100 and ~200 kpc),
assuming hydrostatic balance of the hot gas enshrouding them. They afford, for
the first time to my knowledge, testing MOND in ellipticals with force and
quality that, arguably, approach those of rotation-curve tests in disk
galaxies. In the context of MOND, it is noteworthy that the measured
accelerations span a wide range, from more than 10a0 to about a0/10,
unprecedented in individual ellipticals. I find that MOND predicts correctly
the measured dynamical mass runs (apart from a possible minor tension in the
inner few kpc of NGC 720, which might be due to departure from hydrostatic
equilibrium): The predicted mass discrepancy increases outward from none, near
the center, to ~10 at the outermost radii. The implications for the
MOND-vs-dark-matter controversy go far beyond the simple fact of two more
galaxies conforming to MOND.
