use strict;
use warnings;
# G in m^3/kg/s^2
# c in m/s
# m in kg
my $G=6.67428*10**-11;
my $c= 299792458;
my $PI= 3.14159265358979323846264338327950288;

# in Joule
my $eV=  1.60217653*10**-19;

sub e2m { my $e= shift; return $e/$c**2; }

my $MeV= e2m($eV);
printf("MeV= %10g\n", $MeV);
my $Melectron= 9.10938215*10**-31;
my $Msun= 1.9891*10**30;
my $Mearth= 5.9736 * 10**24;
my $Rearth= 6378100;

# schwarzschild radius
sub Rs { my $m= shift; return 2*$G*$m/$c**2; }

# gravitational potential energy
sub Ug { my ($m1, $m2, $r)= @_; return $G*$m1*$m2/$r; }

# escape velocity: 
sub ve { my ($m, $r)= @_; return sqrt(2*$G*$m/$r); }

# volume of sphere = 4/3*PI*r**3
sub Vsphere { my $r= shift; return 4/3*$PI*$r**3; }

# density: 
sub density { my ($m, $r)= @_; return $m/Vsphere($r); }
printf("earth: %14g\n", ve($Mearth, $Rearth));


# print radius + density for various mass blackholes
for (my $m= $MeV ; 1 ; $m*=2)
{
# note: ve($m, Rs($m)) == $c
    printf("%14g %14g %14g\n", $m, Rs($m), density($m, Rs($m)));
}