So astrophysicists are now contemplating theories in which the unseen mass is a mix of both cold and hot dark matter.

Other astronomers have reported that the Milky Way and neighboring galaxies seem to be falling toward some enormous but unseen mass, known as the "great attractor."

The gravity from a huge unseen mass would speed up and perturb anything within the distance of 10 or 20 light years.

If the stars were moving fast it would mean that there was more unseen mass there to provide the gravity keeping them from leaving the galaxy.

But his words were lost in the cries of the desperate Arkonides pushed ahead by a still unseen mass of people.

He knew because some unseen nearby mass had skewed his Jump point by several million miles.

Zwicky applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass.

But there undoubtedly a lot of unseen mass such as dust, dead stars, and black holes.

They all heard the noise of the torpedo launcher and then watched the tiny silver probe zip toward the unseen mass.

You people," he called out louder still to the unseen masses beyond, "They've come back to us, you understand?