11.   It betrays its presence only by the gravitational pull it exerts on the shapes and movements of galaxies.

12.   Neutrinos, which bombard Earth in astronomical numbers, can pass through matter with only a minuscule chance of hitting any atom and thereby betraying their presence.

13.   Properties of the quasar light should not only betray the presence of these hydrogen clouds but also reveal clues to star formation and galactic evolution.

14.   The astronomers noticed characteristic features in the light spectrum that betrayed the presence of a large intergalactic cloud between the light source and Earth.

15.   They used knives, Kerrey says, evidently to avoid betraying their presence with gunshots.

16.   Only now and then a stray torch beacon betrays their presence as members of the watch signal to each other.

17.   On the top storey, lights betrayed the presence of someone who perhaps was spending one last night in their home or was going to stay.

18.   The bloodhounds will not bark to betray their presence to the enemy, the sergeant said.