Calculate the Schwarzschild radius (in kilometers) for each of the following.1.) A 1 ×108MSun black hole in the center of a quasar. Express your answer using two significant figures.2.) A 6 MSun black hole that formed in the supernova of a massive star. Express your answer using two significant figures.3.) A mini-black hole with the mass of the Moon. Express your answer using two significant figures.4.) Estimate the Schwarzschild radius (in kilometers) for a mini-black hole formed when a superadvanced civilization decides to punish you (unfairly) by squeezing you until you become so small that you disappear inside your own event horizon. (Assume that your weight is 50 kg.) Express your answer using one significant figure.

The energy conservation allows to find the Schwarschild radius for several bodies of different masses are:

  1)  Black hole quasar is:  r = 2.9 10⁸ km

  2) Blsck hole supernove is:  r = 17.7 km

  3)  Mini black hole is:   r = 1.1 10⁻⁷ km

  4) Human body is:  r=  7 10⁻²⁹ km

The schwarschild radius is defined as the distance from a black hole center at radius  which the escape velocity is equal to the light speed, in some cases it is also called the event horizon.

Let's use Newton's second law where force is the universal law of attraction and acceleration is centripetal.

        F = ma

        F =        

Where F is the force, M the mass of the black hole, m the handle of the body, r the radius and v the speed of the body.

The energy of the gravitational field is

        F =  

         U =  

Let's use conservation of energy

        Em₀ = K + U = ½ m v² -    

In infinity the energy

        Em_f = 0

energy is conserved

       Em₀ = Em_f  

       ½ m v² -  = 0

       r =

From the definition of the Schwarschild radius this speed is equal to the light speed

        v = c

        r =  

They ask to calculate the radius for several cases of different mass, claculate the constant value

      V =  

      V =  1.482 10⁻²⁷

1) A black hole of mass M = 1 10⁸

The tabulated mass of the sun is = 1.989 10³⁰ kg

Let's  substitute

        r =  1.482 10⁻²⁷   1 10⁸ 1.989 10³⁰

        r = 2.94 10⁸ km

With two significant figures

        r = 2.9 10⁸ km

2) A black hole of mass M = 6

        r =  1.482 10⁻²⁷ 6 1.989 10-30

        r = 17.7 km

3) a mini black hole with the mass of the moon

    Tabulated mass of the moon M = 7.35 10²² kg

       r =  1.482 10⁻²⁷  7.35 10²²    

       r = 1.1 10⁻⁷ km

4) A person of M = 50 kg

    r =  1.482 10⁻²⁷ 50

    r=  7 10-29 km

In conclusion using the conservation of energy we can find the Schwarschild radius for several bodies of different masses are:

  1)  Black hole quasar is:  r = 2.9 10⁸ km

  2) Blsck hole supernove is:  r = 17.7 km

  3)  Mini black hole is:   r = 1.1 10⁻⁷ km

  4) Human body is:  r=  7 10⁻²⁹ km

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