[TOMT][Book] Scifi book set in space, before the 2000's

There's a book I've been trying to identify for almost a decade now with no luck. It's been a long time since so some of the details might be wrong, but here's a list of all the clues I have:

I loaned the book from a library in the late 90's, before the year 2000. The book was translated into my native language; I think the original language was English. I have a vivid memory of the title being "Black Sun" (as translated into my language) but I'm probably mistaken as nothing has ever come up in a search. The book did not look new.

The genre was a scifi and the story was set in space. The plot focused on a spaceship/station crew studying a weird phenomena related to a black hole. I think there was a character named Nick (might've been the main character). The main character was male. He had survivor's guilt from watching his friend die during a spacewalk gone awry. (I think the friend sacrificed himself to save the main character's life.) There was a scientist character who was described as perpetually messy and who went by a nickname related to the character's tangled hair.

According to my memory the book ends on an ambiguous note. (Main character ends up the sole survivor, hears a mysterious sound implied to be an entity related to the weird phenomena they were studying?)

It is NOT any of the Space Odyssey books and no book by the most famous scifi authors (Clarke, Asimov etc.) matches, yet it had to have been popular enough to be translated. The story had no fantasy elements. I've gone through lists of books about black holes, searched used bookstores with relevant keywords and went through Wikipedia lists with no luck. The book was not a novelization of Event Horizon.