Humanoid Forms And A Mysterious Volume Of Space

"Sargasso of Lost Starships."

This must be the only story by Poul Anderson in which the aliens are not just generally humanoid in form but completely indistinguishable from human beings as in an average Star Trek episode. We take this to be impossible as stated later in the Technic History:

"Unless, to be sure, happenstance had duplicated most of those details for you in the course of evolution...

"Ridiculous, Laure thought. Coincidence isn't that energetic."

-Poul Anderson, "Starfog" IN Anderson, Flandry's Legacy (Riverdale, NY, June 2012), pp. 709-794 AT p. 725.

This is clear evidence that "Sargasso..." should be regarded as a fiction within the fiction. 

Allowing for some cosmetic changes, as to colour and length of hair, one and the same actor would be able to play three of Poul Anderson's villains:

Brann in The Corridors Of Time;

Merau Varagan in the Time Patrol series;

Morzach in "Sargasso..."

- two time travellers and one teleporter-telekineticist. Screen audiences would be free to speculate about one being manifesting in three timelines.

The title of "Sargasso..." had led me to expect a hard sf story about abandoned spaceships orbiting together at somewhere like a Lagrangian point which, if I remember correctly, was how Dan Dare was reunited with his old ship, Anastasia.

The Black Nebula is a region of strange phenomena which turn out to be neither supernatural nor technological but psychic in nature. I have been told that, in Babylon 5, which I have never watched, human space travellers avoid a volume of space where an incomprehensibly advanced civilization operates. Presumably something like this is possible: a species as far advanced beyond humanity as we are beyond cave-dwellers.