Dark matters. Book 2 Ghost dance - Christie Golden

Scientific theory holds that ninety percent of all matter in the universe is "dark matter", which we cannot see but which exerts a gravitational force. The universe seems to be perfectly balanced at the critical density which counters the outward expansion of the galaxies with their inward gravitational pull on one another. Too much matter or too little could bring about the end of the universe - and an alien species has begun to import dark matter from a parallel universe into our own in an attempt to do just that!
Unknowingly, a contaminated USS Voyager has been leaving a trail of the deadly material across the Delta Quadrant ever since their first meeting with Romulan scientist Telek R'Mor. Now Captain Janeway and her crew are forced to retrace their epic journey to recover lost quantities of the dark matter, encountering old foes and allies while striving to outrace the cataclysmic doom which threatens not one but two realities.
Malevolent forces plot against Voyager's quest... Meanwhile, Commander Chakotay and Ensign Paris are still cut off from contact with their captain, their ship - and their universe!