Why do astronauts think there is a great amount of mass in the halo of the milky way?

A great disk made of stars orbiting a central point in the disk. ... Mass of Milky Way ... The halo of the Milky Way contains the oldest-known objects in the ... Astronomers think that the galaxy started out as a spherical cloud in space. ... galaxies, that emit as much or more energy in radio wavelengths then they do in visible light

Maybe because theirs a greater force at the milky-way there is less gravity in other parts of the space beyond were we are at!  

Ifound this on google “according to the findings, a foramen magnum positioned toward the base of the skull is found not only in humans, but in other habitually bipedal mammals as well.” i hope this you for what your looking for