The Hawking energy or Hawking mass is one of the possible definitions of mass in general relativity. It is a measure of the bending of ingoing and outgoing rays of light that are orthogonal to a 2-sphere surrounding the region of space whose mass is to be defined.

Definition

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Let   be a 3-dimensional sub-manifold of a relativistic spacetime, and let   be a closed 2-surface. Then the Hawking mass   of   is defined[1] to be

 

where   is the mean curvature of  .

Properties

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In the Schwarzschild metric, the Hawking mass of any sphere   about the central mass is equal to the value   of the central mass.

A result of Geroch[2] implies that Hawking mass satisfies an important monotonicity condition. Namely, if   has nonnegative scalar curvature, then the Hawking mass of   is non-decreasing as the surface   flows outward at a speed equal to the inverse of the mean curvature. In particular, if   is a family of connected surfaces evolving according to

 

where   is the mean curvature of   and   is the unit vector opposite of the mean curvature direction, then

 

Said otherwise, Hawking mass is increasing for the inverse mean curvature flow.[3]

Hawking mass is not necessarily positive. However, it is asymptotic to the ADM[4] or the Bondi mass, depending on whether the surface is asymptotic to spatial infinity or null infinity.[5]

See also

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References

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  1. ^ Hoffman 2005, p. 21
  2. ^ Geroch, Robert (December 1973). "Energy extraction*". Annals of the New York Academy of Sciences. 224 (1): 108–117. Bibcode:1973NYASA.224..108G. doi:10.1111/j.1749-6632.1973.tb41445.x. ISSN 0077-8923. S2CID 222086296.{{cite journal}}: CS1 maint: date and year (link)
  3. ^ Hoffman 2005, Lemma 9.6
  4. ^ Section 4 of Shi, Yuguang; Wang, Guofang; Wu, Jie (2008). On the behavior of quasi-local mass at the infinity along nearly round surfaces. arXiv:0806.0678.
  5. ^ Section 2 of Finster, Felix; Smoller, Joel; Yau, Shing-Tung (2000-06-01). "Some Recent Progress in Classical General Relativity". Journal of Mathematical Physics. 41 (6): 3943–3963. arXiv:gr-qc/0001064. Bibcode:2000JMP....41.3943F. doi:10.1063/1.533332. S2CID 18904339.

Further reading

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