How this calculator works
This is a rest-mass bookkeeping model. You supply the fraction of infalling rest energy that escapes; it is not predicted from an orbit. Retained mass changes the Schwarzschild horizon. Optional fields use Newtonian gravity at a fixed centre-to-centre distance. The potential energies refer to a hypothetical external test mass equal to the infalling mass, before and after accretion, not to the swallowed object after capture. Near-horizon fields require relativity. A solar-mass reference may be obtained from the IAU nominal solar mass parameter divided by CODATA G; that mass is not an exact nominal kilogram constant.
Formula
Mf = M + (1-eta)m; E = eta m c^2; r_s = 2GM/c^2; g = GM/d^2; U = -GMm/d. The external comparison holds d and the reference test mass fixed.
Worked example
For M = 10 kg, m = 2 kg and eta = 25%, the final mass is 11.5 kg and radiation carries 0.5 c^2 = 4.493775893684088e16 J.
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Frequently asked questions
Does this predict gravitational waves?
No. Spin, orbit and relativistic merger dynamics determine the waveform and radiated fraction. Here that fraction is an input.
Why can the final mass be less than the sum?
Escaping radiation removes energy, so the retained gravitational mass is smaller than the combined rest masses.
Is the event horizon a material surface?
No. It is a causal boundary. The Newtonian comparison is an approximation for external points, most useful well away from it.