Schedule by Session

I will discuss the orbital motion of the 10 Milky Way satellites with HST proper motions, which includes the two Magellanic Clouds. The Galactic satellites have very circularly biased motions, with a velocity anisotropy, beta = -2.2, that is discrepant with the predictions of the standard cosmological model, LCDM. Individually, the Milky Way satellites have radial velocities that are lower than expected for their proper motions, with 9 out of the 10 having at most 20 per cent of their orbital kinetic energy invested in radial motion. Such extreme values are expected in only 1.5 per cent of LCDM satellites systems. This tangential motion excess is unrelated to the Galactic ‘disc of satellites’ and represents another Galactic-scale puzzle for the standard cosmological model.