Built on

Newman, E. T., Penrose, R.: J. Math Phys. 7
1966
Earlier work this paper cites.
Penrose, R.: Gen. Rel. Grav. 7
1976
Earlier work this paper cites.
Geroch, R., Winicour, J.: J. Math. Phys. 22
1981
Earlier work this paper cites.

Similar

Ko, M., Ludvigsen, M., Newman, E. T., Tod, K. P.: Phys. Repts. 71
1981
Cited alongside, same era.
Penrose, R.: Proc. R. Soc. Lond. A381
1982
Cited alongside, same era.

Then

Penrose, R., Rindler, W.: Spinors and space–time, University Press, Cambridge (1984–6)
1984
Later among the works it cites.
Szabados, L.: Liv. Rev. Rel. 7
Original
2004
Later among the works it cites.

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2007

Angular momentum of isolated systems

Helfer, Adam D.

Understand

Penrose's twistorial approach to the definition of angular momentum at null infinity is developed so that angular momenta at different cuts can be meaningfully compared.

This is done by showing that the twistor spaces associated with different cuts of scri can be identified as manifolds (but not as vector spaces).
The result is a well-defined, Bondi-Metzner-Sachs-invariant notion of angular momentum in a radiating space-time; the difficulties and ambiguities previously encountered are attached to attempts to express this in special-relativistic terms, and in particular to attempts to identify a single Minkowski space of origins.
Unlike the special-relativistic case, the angular momentum cannot be represented by a purely j=1 quantity M_{ab}, but has higher-j contributions as well.