User blog comment:ArceusBowser44/First Calc--Black Hole Ability/@comment-33067344-20180911142710/@comment-33067344-20180911155432

Ah, my bad.

(299792458² * 2.88) / (2 * 6.67408e-11) = 1.93915485e27 kg

U = (6.67408e-11)*(1.93915485e27^2)/(5*2.88) = 1.74282547e43 joules. Still Large Star level.