Passing in the Night by Michael Kingswood

A year-long shift in the middle of the interstellar void can get pretty boring. For the Fourth shift crew of the starliner Pericles, enroute to Earth from one of the colony worlds, the passage could best be called routine.

Until the forward sensors detect an unknown and unexpected object ahead. What they find there, in the endless night of space, will forever change the universe, for them and for all mankind.

Assuming they survive to tell anyone about the encounter.