The Black Hole at the Center of the Milky Way

  Mass  =  4 billion solar masses  
  Radius  =  G M / c2  =  6 million km  =  10 solar radii  
  Natural timescale  =  G M / c3  =  20 seconds  

  Dimensionless accretion rate  =  20 seconds
Age of Universe
  =  10-16  
  Inflationary scale length  =  10-16  ×  Radius  =  10-4  millimeters  

  Þ   In less than 1 millimeter, the density at the inner horizon
will exponentiate to vastly greater than the Planck density.  

  Penrose diagram of an extremal black hole