Black Hole Candidate?

Question

What observation would give the soundest indication that an object is a black hole candidate?

A. Irregular bursts of X ray emission

B. Disappearance at visible wavelengths

C. Regular pulses of radio emission

D. Spectral emission lines that are alternately blueshifted and redshifted

E. Periodic variations of infrared radiation

Answer 1

I'll go with A

Also:

Immense gravity well bending light around it, or "lensing."

Answer 2

A - true.  I would expect this to happen every time something falls in

B - maybe.  Anything falling in might glow.  Otherwise, true.

C - false.  I don't see why it would do this.  

D - maybe.  If something is orbitting a black hole (or anything else) it will have a blue shift coming towards us (1/2 the orbit) and a red **** going away from us (other 1/2 the orbit).  From the event horizon, everything will be horribly red shifted though.

E  - maybe.  If varying amounts of matter are falling in, I would expect the matter falling in to have varying temperatures.

Out of these, I mostly agree with A like everyone else.

Answer 3

I think its 'A' as well.

Answer 4

A.

If the variations are fast enough, it suggests that a small object is making them.

Answer 5

A., B.,  &  D.