What could galaxies along the line of sight between Earth and distant objects like quasars have anything to do with those objects themselves? Yet in a remarkable finding, the sightlines to quasars seem to be four times less likely to be populated with galaxies than the sightlines to gamma-ray bursts. Odd? Believe it. “The result contradicts our basic concepts of cosmology, and we are struggling to explain it,” said Jason X. Prochaska (UC-Santa Cruz).

The Swift satellite is the vehicle for this work, which used mission data to study the transient yet bright afterglow of long-duration gamma ray bursts (GRBs). Now the paper, by Prochaska and graduate student Gabriel Prochter, is awaiting publication in Astrophysical Journal Letters, but its appearance as a draft on the arXiv site is already spawning new work attempting to answer its questions.

Working with 15 GRBs, the duo found strong absorption signatures indicating the presence of galaxies along 14 of the GRB sightlines. Such signatures occur because some frequencies are absorbed by the gas associated with a galaxy, providing a marker for the galaxy even when there is little visible evidence. But data from the Sloan Digital Sky Survey showing the incidence of galaxies along the sightlines to quasars had the team expecting fewer than four galaxies.

What causes the higher number relating to GRBs? One possibility among three discussed here may be in the way the intervening galaxy acts as a gravitational lens, enhancing the brightness of the background object. If that lensing produces different effects for quasars than GRBs, this could provide an answer, but Prochaska says gravitational lensing experts tell him such a variation is unlikely to hold up, nor do two other explanations involving galactic dust or dust associated with the GRBs themselves. What’s needed to move on to a more convincing explanation is to extend the GRB sample significantly, using data from the extended Swift mission.

Prochaska would like to quadruple the sample size. A good idea indeed, for as the paper notes: “At present, we have not identi?ed a satisfactory single explanation for this phenomenon. Our results suggest that at least one of our fundamental assumptions underpinning extragalactic absorption line research is ?awed.”

Centauri Dreams note: This is another instance of print publication being significantly anticipated by the online preprint process. As scholarly publishing evolves in digital directions, notice how ideas are refined through online venues from e-mail to mailing list, weblog, authorial archive and pre-print server long before they finally see fixed publication in a journal. The added benefit to preprints is, of course, that the audience of judges for submitted papers is enormously extended, and authors can receive input far more quickly than before.