 The age of the Hyades is estimated to be about 625 million years.The core of the cluster, where stars are the most densely packed, has a radius of , and the cluster's tidal radius – where the stars become more strongly influenced by the gravity of the surrounding Milky Way galaxy – is .However, about one-third of confirmed member stars have been observed well outside the latter boundary, in the cluster's extended halo; these stars are probably in the process of escaping from its gravitational influence.