A star orbiting around an invisible massive companion. Powerful X-rays emitted by gas heated to extreme temperatures as it falls into the hole. Gas from the visible star is dumped on the companion, heats up, and emits X-rays. Estimate the mass of the unseen companion from the orbit. 3 M sun , too big for a Neutron Star.
None are as yet iron-clad cases.
But, General Relativity does not include the effects of Quantum Mechanics. Stephen Hawking Took into account quantum effects occurring near the event horizon of a Black Hole. The smaller the mass of the black hole, the faster it leaks. The Smaller the mass, the faster the evaporation. Copyright 1998 Richard W. Pogge, All Rights Reserved.