Sharp bounds on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mn>2</mml:mn><mml:mi>m</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>r</mml:mi></mml:math> of general spherically symmetric static objects