Never have so many astronomers been so eager to claim they can't see straight. Groups working with three different telescopes have detected weak lensing, a distortion of distant galaxies that reveals dark matter strewn across deep space. The results provide a first direct glimpse of the vast tangle of massive, invisible stuff that astronomers and astrophysicists believe makes up most of the mass of the universe.
Almost as interesting as the results themselves is how the researchers chose to make them public: Within days, all three groups rushed their findings into print--or, rather, into preprint--on Astro-Ph, an unrefereed Web server maintained by Los Alamos National Laboratory in New Mexico. Two did so with some misgivings, to avoid being scooped.
Such posting frenzies are becoming common, says Tony Tyson, an astrophysicist with Lucent Technologies' Bell Labs in Murray Hill, New Jersey, and leader of one of the teams. "Various groups have their results in various stages, and then somebody jumps in [with a preprint], and then everybody jumps in." A team working with the Canada-France-Hawaii Telescope (CFHT) in Hawaii made the first splash, followed by a group working with the William Herschel Telescope in the Canary Islands. Tyson's group, working at the Cerro Tololo Inter-American Observatory's Blanco Telescope in Chile, was the third to post its results.
Pricking the three groups' heels was the knowledge that weak lensing may prove the best tool for studying the colossal dark matter infrastructure of the universe. Researchers hope to use the technique to measure the distribution of the ripples and undulations in the intergalactic tangle of dark matter--information that would tell cosmologists precisely how the universe grew up after its birth in the big bang.
To glimpse dark matter, the three teams studied light from galaxies billions of light-years away. Such galaxies appear as faint luminous ellipses in the sky; gravity from intervening dark matter deflects their light, slightly squashing the ellipses in any small patch of sky so that, like schooling fish, neighboring ellipses tend to point in the same direction. But to see the gravitational effect, the astronomers first had to filter out similar but much larger distortions caused by optical imperfections and the atmosphere. For that, they turned to stars within our own Milky Way galaxy that lie close to the line of sight of the distant galaxies. At such close range, weak lensing could not affect the stars' images; any distortions had to be due to optical and atmospheric effects. By calculating how to turn the blurred images of the stars back into points and then adjusting the shapes of the distant galaxies in the same way, the researchers could isolate the distortion due to dark matter--a distortion so slight that each group surveyed tens of thousands of galaxies to see it.
The three groups spent years analyzing their data. They picked up the pace as soon as the competition for recognition was on. On 27 February, the CFHT team posted a preprint detailing its results on Astro-Ph. Within 5 days, the Herschel and Blanco groups followed suit. On 7 March, the CFHT group issued a press release claiming to have seen weak lensing first.
The three preprints are just a drop in a still-gathering tsunami of unofficial publications in astronomy, astrophysics, and other physical sciences. In 1995 researchers posted 1663 papers on Astro-Ph; in 1999 they posted 5639. Last month alone, 531 papers appeared on the site.
"[Astro-Ph] has taken over [from the journals] as far as I'm concerned," says Nick Kaiser, an astronomer at the University of Hawaii, Manoa. "Every morning the first thing I do is read the Astro-Ph e-mail I get." The server will soon put traditional journals out of business, Kaiser predicts, and formal peer review will give way to some sort of electronic dialogue. That wouldn't surprise Princeton astrophysicist David Spergel. "For me personally, publication doesn't matter," he says. "I've pretty much stopped reading the journals."
The leaders of the three weak-lensing teams don't go that far. Tyson thinks it's presumptuous to post a paper before it's been accepted for journal publication. In fact, he says, his group's paper was in review with a journal when the CFHT preprint forced his hand. Richard Ellis, an astronomer at the California Institute of Technology in Pasadena and leader of the Herschel telescope team, tells a similar story and says he is leery of what can happen when fear of being wrong loses out to fear of being late. "There's a terrible danger that the standards go down," he says, "that it becomes just a race."
Yannick Mellier, an astronomer at the Institut d'Astrophysique de Paris and leader of the CFHT group, is more sanguine. Researchers should post as soon as they are confident of their results, he says; fear of humiliation will prevent them from posting weak or incomplete work. "If you do a bad job in this aspect, submitting a bad or nasty paper, you are almost immediately criticized by your colleagues." But even he would regret the passing of the traditional journal, he says, "because [journal publication] means a paper has been completely refereed; it has been officially accepted."
Whether or not traditional publications survive, weak lensing seems sure to thrive. Each of the three groups has already collected more data with which to sharpen and expand its results. Moreover, the Sloan Digital Sky Survey, a nine-institution collaboration working with a telescope at the Apache Point Observatory in New Mexico, intends to survey a full quarter of the celestial sphere and capture images of roughly 80 million galaxies by 2005. Within a decade, astronomers and astrophysicists may be telling long, detailed stories about the universe's childhood. And you're likely to read them on a server like Astro-Ph first.
Copyright © 2000 by the American Association for the Advancement of Science.