Astronomers know that if they point their telescopes at quasars, they will spy an average of one “foreground” galaxy in front of every fourth quasar. Because the universe is uniform, the number of foreground galaxies should be the same for, say, a group of observed gammaray bursts. Only it is not. In a paper that is generating considerable buzz among the stellarati, Jason X. Prochaska of the University of California, Santa Cruz, finds an average of about one foreground galaxy for each of 15 bursts. If the result holds, then astronomers are misinterpreting a key aspect of foreground gas—potentially posing a serious cosmological problem, because they use the gas to estimate the composition of the earliest galaxies and the distribution of dark matter, which makes up 90 percent of the matter in the universe. Foreground galaxies might be unexpectedly dusty, obscuring some quasars; they might be focusing light from gamma-ray bursts, causing astronomers to miss fainter ones. Or the supposed galaxies might be gas from the bursts themselves, the researchers note in the September 20 Astrophysical Journal Letters.
This article was originally published with the title "That Way Lies Confusion" in Scientific American 295, 4, 34 (October 2006)