41.   Dr. Bruce Margon, an astrophysicist at the University of Washington in Seattle, said the problem of dark matter was still far from solution.

42.   Dr. Olling and Dr. Merrifield estimated that the thickness of the hydrogen layer would depend on the arrangement of the dark matter.

43.   Filaments of dark matter stretch across the simulated scene, galaxies forming where they intersect and the dark matter is densest.

44.   Finding evidence of this dark matter could help scientists calculate how much mass is in the universe, Davidsen said before the flight.

45.   Future Chandra observations may clarify whether more than gravity binds the particles of dark matter.

46.   Gas and dark matter flow along these filaments, and where they intersect, galaxies and clusters of galaxies form.

47.   If dark matter is more tenuous, the universe could keep expanding into nothingness.

48.   Identifying the nature and amount of dark matter is the central problem in cosmology today.

49.   In a heroic act of scientific imagination, astronomers inferred instead the existence of some kind of undetectable stuff called dark matter whose gravity holds the galaxies together.

50.   If the conflict persists, the solution may involve far more than simply picking a new set of particles as the dark matter.