A new study found an excess of counter-clockwise rotating or “left-handed” spiral galaxies like this one, compared to their right-handed counterparts. This provides evidence that the universe does not have mirror symmetry. Image: NASA, ESA
Physicists and astronomers have long believed that the
universe has mirror symmetry. But recent findings from the University of Michigan
suggest that the shape of the Big Bang might be more complicated than
previously thought, and that the early universe spun on an axis.
To test for the assumed mirror symmetry, physics professor
Michael Longo and a team of five undergraduates catalogued the rotation
direction of tens of thousands of spiral galaxies photographed in the Sloan
Digital Sky Survey.
The mirror image of a counter-clockwise rotating galaxy would
have clockwise rotation. More of one type than the other would be evidence for
a breakdown of symmetry, or, in physics speak, a parity violation on cosmic
scales, Longo says.
The researchers found evidence that galaxies tend to rotate
in a preferred direction. They uncovered an excess of left-handed, or
counter-clockwise rotating, spirals in the part of the sky toward the north
pole of the Milky Way. The effect extended beyond 600 million light years away.
“The excess is small, about 7%, but the chance that it
could be a cosmic accident is something like one in a million,” Longo says.
“These results are extremely important because they appear to contradict
the almost universally accepted notion that on sufficiently large scales the
universe is isotropic, with no special direction.”
The work provides new insights about the shape of the Big
Bang. A symmetric and isotropic universe would have begun with a spherically
symmetric explosion shaped like a basketball. If the universe was born
rotating, like a spinning basketball, Longo says, it would have a preferred
axis, and galaxies would have retained that initial motion.
Is the universe still spinning?
“It could be,” Longo says. “I think this
result suggests that it is.”
Because the Sloan telescope is in New Mexico, the data the researchers
analyzed for their recent paper came mostly from the northern hemisphere of the
sky. An important test of the findings is to see if there is an excess of
right-handed spiral galaxies in the southern hemisphere. This research is
A paper on the findings, “Detection of a Dipole in the
Handedness of Spiral Galaxies with Redshifts z~0.04” is published in Physics Letters B.