The conserved angular momentum L obeys a simple formula for a constant vertical (or else horizontal) rotation axis of the wheel:

L = ω m r^2

Since this expression is hard to remember by heart, the word “L’hombre” can help even though it is not high-Spanish. ω is the rotation rate, m the mass and r the radius of Noether’s frictionlessly rotating bicycle wheel.

If ω is halved (as on the surface of a neutron star), what about m and r , the other two components of the conserved L ?

You guess it: m is halved and r doubled. How come? The halved mass follows from the halved frequency and hence energy of the photons produced down there. They are locally transformable into particles with mass, via quantum mechanics’ creation and annihilation operators. The resulting half-mass atoms have a doubled Bohr radius: so r is doubled if ω is halved.

But does this doubled size of the wheel rotating downstairs at halved speed not contradict the fact, implicit in the theory which underlies the accelerating Einstein rocketship (special relativity), that light has to travel up and down along straight vertical lines?

The latter fact indeed remains in charge. It thereby entails that the doubled radius of the horizontally rotating wheel must be optically masked when viewed from above. So the wheel looks non-enlarged horizontally when viewed from above – even though its radius r is doubled.