"But the Einstein Lens effect doesn't make smudges like this," objected Majors.
Pollard whistled. "You mean to say that the Einstein Lens is known to be a fact?"
"Right. Several cases are known and accepted as such!"
"Well!"
Carroll looked up from the smudge. "A negative lens," he said, "would cause diffusion like this."
Majors blinked. "That would mean—oh, no!"
"Negative matter," said Carroll promptly.
"Um. You postulate a negative mass in line with the light from a star?"
Carroll nodded.