As if looking at a cosmic packing crate, two scientists may have found a "this end up" sign for the universe.
For years, the concept that there is no up, down, or preferred direction in space - that the universe applies its rules equally in all directions - has been a pillar of astrophysics. But new research by physicists Borge Nodland and John Ralston may challenge this notion of an "isotropic" universe.
Scientists use that pillar to support some of their most basic theories about how the universe was formed and has evolved. To find an exception to the universe's evenhandedness that extends across billions of light-years would send a lot of scientists back to the blackboard.
The two researchers analyzed radio waves from 160 galaxies as far away as 100 million to 1 billion light-years. As the emissions sped through space, they traveled in a never-before-detected corkscrew pattern, the team concluded. The pattern became apparent after other, well-known influences on the orientation of radio waves in space were taken into account.
Moreover, the rotation of the radio waves appears to depend on the direction from which the waves come, the scientists observed. The rotation rate was greatest along an imaginary line that stretches between well-known constellations in opposite directions in the night sky.
"Our data suggest that there is a mysterious axis, a kind of cosmological North Star that orients the universe," says Dr. Ralston, a professor of physics and astronomy at the University of Kansas at Lawrence. Yet the effect is so subtle, he adds, that "this may be the smallest thing anyone has ever discovered."
The finding, reported in today's edition of the journal Physical Review Letters, has raised eyebrows among some members of the astrophysics community.
"This flies directly in the face of extremely precise measurements" of the big bang's afterglow, known as microwave background radiation, says University of Chicago astrophysicist David Schramm. Those satellite measurements showed that the radiation was remarkably uniform in every direction.
Yet Ralston holds that there is no contradiction. "We're measuring a different phenomenon" than did the satellite, he says.
IF the duo's work holds up to further scrutiny, scientists may have to revise their notions of how the universe formed.
"Perhaps it was not a perfect big bang, but a big bang with a twist to space and time," says Dr. Nodland, a research fellow at the University of Rochester's Rochester Theory Center for Optical Science and Engineering in New York. If so, he adds, the "axis" may be a remnant of that twist.
The two identified the axis as they tried to identify why microwave emissions from distant galaxies travel in a corkscrew-like swirl. Astronomers use these emissions as a window on everything from the chemical makeup of the galaxies to the violent processes that shape these vast collections of stars.
Using computer models, Nodland and Ralston tried to flatten out the emissions' orientation, or polarization, by subtracting known effects of galactic magnetic fields and clouds of electrically charged particles. When they finished, they were left with a very slight twist in polarization - about one turn for each 1 billion light-years the signal traveled.
Assuming an isotropic universe, "the effect should have been the same in any direction," Nodland says. Instead, they noticed that the polarization became more pronounced the closer the source galaxy was to an imaginary line that runs from the constellation Sextus at one end, through Earth, and toward the constellation Aquila at the other end.
Ralston adds that it is unclear whether the "axis" is truly a part of the universe's structure or perhaps hints at the effects of a class of subatomic particles that so far exist only as equations on theorists' blackboards.
Mindful of the potential their work has for undermining the concept of an isotropic universe, Ralston and Nodland say they are looking forward to increasing the number of galaxies in their analysis, particularly galaxies at greater distances than the ones used in their current study.
"I expect with the reaction we're getting, we'll get a lot more data" from radiotelescopes around the world, Ralston says.
In the meantime, astronomers are preparing to look for polarization changes in the cosmic background radiation as a test of models that try to reconstruct how the density of matter in the early universe changed.
If the universe is not isotropic, "that would imply effects on the microwave background," says the University of Chicago's Dr. Schramm. Unless the effect can be detected at other wavelengths or until the polarization of the background radiation is checked for the axis effect, "most of the astrophysics community will be looking at this with skepticism," he says.