Scientists who caused a global sensation when they announced the discovery of gravitational waves may have been fooled by bits of dust floating about in space.
Researchers at Harvard University called a press conference in March to reveal that they had spotted the cosmic signature of ripples in space left over from the spectacular expansion of the early universe. The dramatic claim was hailed as one of the most important scientific discoveries of the century and promised a new era of physics.
However, the findings, which some experts doubted from the off, have received a serious blow from researchers with the European Space Agency’s (ESA) Planck mission, who found that galactic dust could fully explain the observation.
“It’s certainly possible that the results can be explained purely by dust,” said Jo Dunkley, professor of astrophysics and a member of the Planck team at Oxford University. “Our work doesn’t rule out the possibility that they have gravitational waves, but there is dust in there and it seems to be higher than thought.”
Cosmologists on Harvard’s Bicep2 team got excited when they spotted a twist in the polarization of light picked up by their telescope at the South Pole. The distinctive twist can be caused by gravitational waves, which squeeze and expand space as they spread out, creating patches of hotter and cooler space. The existence of gravitational waves was predicted by Albert Einstein’s 1916 general theory of relativity.
Light can be twisted by other means. Cosmologists always knew that clouds of dust spewed from exploding stars can mimic the signature of gravitational waves. Space dust is heated up by starlight, but re-emits the radiation as infra-red light. This light gets twisted because dust particles align themselves with the huge magnetic field that stretches through the plane of the Milky Way.
The paper from the Planck team reveals how much polarized light could come from dust alone.
“People thought there might be very clean regions of space, but what we find is that there are no truly clean regions free of polarized dust emission. And that includes the Bicep field,” said George Efstathiou, head of the Cambridge Planck Analysis Centre. “The level of dust that we infer in the Bicep region, or in any other clean region of the sky, is important: it’s comparable to the signal that Bicep have detected.”
Efstathiou said the Planck team’s results did not rule out the Bicep2 findings, but made clear how much dust had to be accounted for.
Andrew Pontzen, a cosmologist at University College London, said the Planck paper added to the weight of evidence that seemed to be going against the Bicep result.
“What you can say for sure is that the original analysis was insufficient to say the signal is really there. It doesn’t mean for sure that they haven’t seen anything,” he said.
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