Not Gravitational Waves After All? New Data Points To Galactic Dust On BICEP2’s Lens

It increasingly looks like the swirling cosmic pattern seen by scientists using the BICEP2 telescope is not a signal of gravitational waves—and, consequently, evidence for the rapid inflation of our universe right after the Big Bang—but rather an artifact of magnetized dust spread throughout our galaxy that originates from dying stars.

In March, the BICEP2 team pointed to a swirling pattern they detected in the cosmic microwave background radiation, which reverberates from the Big Bang to this day. If confirmed, the BICEP2 results would have been an exciting piece of evidence for cosmic inflation, vindicated one of Einstein’s predictions, and given scientists a key to unlocking the secrets of quantum gravity. But only if the discovery was confirmed, as many physicists were careful to point out.

There always remained the possibility that the signal was not from gravitational waves, but something else. Now, another research team has released a new analysis of data collected by the Planck space telescope showing a full sky map of the interstellar dust around us. And the region examined by BICEP2, omitted by previous dust maps, turns out to be really dusty—enough that the polarization of said dust by the magnetic fields of the Milky Way can start to resemble the B-mode polarization pattern predicted by inflationary theory.

University of California, San Diego astrophysicist Brian Keating, part of the BICEP2 team, told Quanta Magazine that the Planck data analysis is “relatively definitive in that we can’t exclude [the possibility] that the entirety of our signal is from dust.”

Even before this new analysis, some other scientists had criticized the BICEP2 team for underestimating amount of galactic dust their telescope was peering through, and for trumpeting their results too soon. (You can see that skepticism on display in the video above, from Princeton University physicist Paul Steinhardt, in the 2014 World Science Festival program on inflation and BICEP2, “Ripples from the Big Bang.”) There is still some chance that there is a gravitational waves signal lurking underneath the dust polarization, but it will be hard to separate that pattern out. The BICEP2 and Planck researchers are collaborating on a joint analysis, expected in November, that may shake the last bits of dust off of the discovery; whether anything remains of the evidence for gravitational waves after that is still uncertain.

The new Planck analysis probably won’t undermine the confidence of inflationary theory advocates, says Columbia University physicist and World Science Festival co-founder Brian Greene. And besides, “the door’s not shut” yet on finding the signal buried deep under the dust, Greene says.