Are there any methods of direct detection for black holes?
I'm not referring to gravitational lensing, or measuring the orbits of a star in a binary pair.
Is there any way of directly 'seeing' them?
Answer
A colleague in astronomy had a student a few years ago who did a calculation about the possibility of primordial black holes, created in the Big Bang. If the size of these was just right, they could be evaporating into nothing due to Hawking radiation right "now" (scare quotes because this would necessarily include distant black holes that evaporated many years ago, whose light is just reaching us now). The last burst of Hawking radiation for these would look basically like a faint gamma-ray burst, in which case it ought to be directly detectable.
I'm not sure of the current status of this-- their preliminary result was, if I remember correctly, that you might be able to test this by measuring the probability distribution for gamma-ray bursts of the appropriate size and duration, but we didn't have any telescopes capable of picking them up at the time. I'm not sure if that's changed or not.
Anyway, that would give you a direct way to detect black holes of a certain size, though they wouldn't be around after the detection, so it might not really fit the spirit of the question...
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