91.   The idea that there may be regions where time runs backward could explain invisible dark matter.

92.   The idea that there may be regions where time runs backwards could explain invisible dark matter.

93.   The map shows that dark matter is more common in the center of the cluster, and it offers the best look yet at how dark particles clump together.

94.   The missing mass is sometimes called dark matter.

95.   The nature of the elusive dark matter and its role in shaping the universe are among the foremost mysteries in cosmology.

96.   The leading candidate for the dark matter until now, called cold dark matter, is simple.

97.   The reason is something called dark matter.

98.   The rest is presumably mostly cold dark matter, unknown and so far undetectable.

99.   The search for dark matter has Nobel prize written all over it.

100.   The search for such dark matter involves astronomers at several American universities and scientists and telescopes in Australia, Chile, New Zealand and Israel.