Any of your ideas would probably manage to make our sun go nova.
Neutron star for certain.
Atom sized black hole…don’t know if they come that small but if it fell into the center of our sun and started collpasing the core then the outer layers probably would blow off.
Stream of hydrogen gas…depends on how much mass the stream adds to the sun. You’d have to add a helluva lot of mass before you got our sun in the area where it would go nova and even then you’d still have to likely wait many millions if not billions of years to see it happen anyway. If you added mass really fast then you’re back into the area of having something like another sun slam into ours which would be a bad thing for us mortals on earth and would almost certainly cause an large stellar explosion.