We've already watched, in the first episode, as Beth wanders downstairs to the basement to find a taciturn janitor with a haunted expression brooding over a chessboard, but rather than molest her, he teaches her to play.
" Magnificent in his reserve and silent sense, " he wrote of their first encounter, " he gives you a look of sombre dignity that makes you feel in some real sense his inferior."
For the stalwart crew and their slim, quiet commander, that must have been a time of great excitement which followed the return of the sun to the vast whiteness that made up the Ross Ice Field.
He seems tired and withdrawn. His eyes do not seem to really look at her. They seem ... lifeless. On Friday night she decides they need to have a talk.
While we lack any explicit evidence due to its withdrawn nature, we have a multitude of indirect evidence that suggests that Cygnus X-1 is definitely a black hole.
In his memoirs, Gilmore recorded how Dean was uncommunicative with the cast or how he read his lines flatly and slowly, mumbling through dialogue or improvising without warning.