  A Schwarzschild Black Hole (BH) is the gravitational field due to a neutral
point mass, and it turns out that the gravitational mass of a neutral point
mass: $M=0$ (Arnowitt, Deser, Misner, PRL 4, 375, 1960). The same result is
also suggested by Janis, Newman, and Winicour (PRL 20, 878, 1968). In 1969, Bel
gave an explicit proof that for a Schwarzschild BH, $M=0$ (Bel, JMP 10, 1051,
1969). The same result follows from the fact the timelike geodesic of a test
particle would turn null if it would ever arrive at an event horizon (Mitra,
FPL, 2000, 2002). Non-occurrrence of trapped surfaces in continued
gravitational collapse too demands $M=0$ for black hole (Mitra, Pramana, 73,
615, 2009).
  Physically, for a point mass at $R=0$, one expects ${\it Ric} \sim M \delta
(R=0)$ (Narlikar \& Padmanabhan, Found. Phys., 18, 659, 1988). But the black
hole solution is obtained from ${\it Ric} =0$. Again this is the most direct
proof that $M=0$ for a Schwarzschild black hole. Implication of this result is
that the observed massive black hole candidates are non-singular quasi black
holes or black hole mimickers which can possess strong magnetic fields as has
been observed. The echoes from LIGO signals, if true, may be the direct
evidence that the pertinent compact objects are BH mimickers and not true
vacuum BHs.
