I don't see why an unfriendly AGI would be significantly less likely to leave a trail of astronomical evidence of its existence than a friendly AI or an interstellar civilisation in general.
I can think of three explanations, but I'm not sure how likely they are: Gamma ray bursts are exploding unfriendly AGIs (i.e. there actually is astronomical evidence), unfriendly AGIs destroy themselves with high probability (lack of self-preservation drive) or interstellar space travel is impossible for some reason.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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