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I think the rule of thumb for maximum practical magnification is 50 times the aperture in inches.
So, for a Celestron 130 that would be 50 x 5 (130mm = 5.1") giving you a maximum practical magnification of 250.
The magnification of a telescope can be found by dividing the focal length of the scope by the focal length of the eyepiece.
I believe your scope has a focal length of 650mm and by juggling the formula and dividing this by the practical maximum magnification, we can arrive at the corresponding eyepiece focal length.
In this case this would be 650 divided by 250 which comes out at around 2.6mm
A 5mm focal length eyepiece on your scope would give you a magnification of 650/5 or 130, which should be well within the capability of the scope.
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