If we aim a radio telescope at a distant spiral arm of the Milky Way Galaxy, we will probably observe a 21-cm line. If we point a large optical telescope at this same region, we will probably not be able to detect the neutral hydrogen that gives rise to the 21-cm radio signal. Why not

a. spokes of a wheel.

as indicated in the question radial contains rad, also found in radius, so the fracture's would span the radius.

well, their are quite a few differences !

explanation:

first difference is a main sequence star is made of carbon, while a neutron star is made of neutrons. another difference is a main sequence star still has hydrogen to burn, while a neutron star is a remnant of a supernova.

a main sequence star is what’s left over from a low-mass star death, while a neutron star is what’s left from the death of a high-mass star. main sequence star and a neutron star are considered the same thing, except a main sequence star spins.