How much energy is radiated when matter falls into a black hole When a black hole consumes matter, it can form an accretion disc. Is there a relationship between the mass of the falling matter $m$, the mass of the black hole $M$, and the energy radiated during the process (until all mass is consumed)? On what other factors the amount of radiated energy depends?
 A: For a Schwarzschild black hole with $a=Q=0$ the innermost stable orbit is at
$$0=r \left(3 a^2-9 Q^2-r^2+6 r\right)+4 Q^2 \left(Q^2-a^2\right)-8 a \left(r-Q^2\right)^{3/2} \to r = 6 $$
where the orbital velocity (in units of c) is
$$\vec{v}_{\perp} = \{ 0, \ 0, \ \sqrt{\frac{1}{r-2}} \} = \{ 0, \ 0, \ 0.5 \} $$
A radially infalling particle has the free fall velocity
$$\vec{v}_{\parallel} = \{ \sqrt{\frac{2}{r}}, \ 0, \ 0 \} = \{ 0.57735, \ 0, \ 0 \} $$
so if they collide they meet with a relative velocity of
$$ \vec{v}_{\rm rel} = \frac{\frac{\gamma \ \vec{v}_{\perp} \times (\vec{v}_{\perp} \times \vec{v}_{\parallel})}{\gamma +1}+\vec{v}_{\perp}+\vec{v}_{\parallel}}{\vec{v}_{\perp}.\vec{v}_{\parallel}+1} $$
with the Gamma factor
$$\gamma =\frac{1}{\sqrt{1-\left\| \vec{v}_{\perp} \right\| ^2}}$$
so the total relative collision velocity is
$$ \vec{v}_{\rm rel} = \{ 0.5, \ 0, \ 0.5 \} \to v_{\rm rel} = ||\vec{v}_{\rm rel}|| = \sqrt{0.5} = 0.707$$ 
and the kinetic energy at impact is
$$E_{\rm kin} = \surd 2-1 = 41.42 \% $$
of the rest-mass of the colliding particles. If all that energy is converted into radiation and reflected to the observer at infinity, that energy has to be redshifted by the lapse function
$$\surd g^{t t} = \sqrt{r/(r-2)}$$
so the energy which the observer at infinity receives is
$$E_{\rm rec} = E_{\rm kin}/\surd g^{t t} = 33.82 \% $$
For rotating $(a \neq 0) $ and/or charged $ (Q \neq 0 ) $ black holes the prograde ISCO may be much closer, and the collision velocities higher.
A: If for example a black hole is consuming a large star an accretion disc can certainly form. The radiated energy is not so much from inside the black hole but more from the matter that is unable to get close enough. The high speeds of rotation around the event horizon and strongly energized matter already there counteracts the gravitational force and can send approaching matter into new trajectories. Quasars are a good example of this. It is only at the event horizon itself that gravity becomes inescapable for all matter. 
A: We can never know it by any kind of experiment . because not a photon,which is the smallest particle carrying  energy is able to escape black hole then how are we gonna get to know it
But we might be able to get it by the electromagnetic wave detection
