The Big “Gravitational Wave” Finding May Have Actually Just Been Some Dust
A supernova remnant interacting with interstellar dust could have caused the signals interpreted to be gravitational waves
A few weeks ago a team of researchers led by the Harvard-Smithsonian Center for Astrophysics' John Kovac announced a stunning discovery: the indirect measurement of gravitational waves, a clear sign of the Big Bang.
The team had used the BICEP2 detector located at the South Pole to measure subtle variations in the polarization of radiation in the cosmic microwave background, and they interpreted these minor variations in the light as a stand-in measurement for the detection of gravitational waves. (Here's a simple, quick explanation.) The announcement was huge, important, Nobel Prize-worthy, fundamental-understanding-of-the-universe-level stuff.
The only problem is that it might have been wrong. The variations in the cosmic microwave background radiation might not have been gravitational waves after all, says New Scientist. They might have been caused by a cloud of dust.
The BICEP2 researchers were looking at the polarization of light to make their gravitational wave claim. As good scientists, they also looked in the sky for other things that could have caused the light to polarize, sources of noise that would have skewed their results. They found a bunch, and corrected for them. But, writes Maggie McKee for New Scientist after talking to Philipp Mertsch, the author of a new study*, they missed one:
[T]he models they used didn't account for dust shells produced as the expanding remnants of supernovae slam into surrounding gas and dust. Magnetic field lines threading through those shells should get compressed and aligned, causing some of the material to line up as well. If the aligned dust contains iron, the particles' slight vibrations due to their own heat would produce polarised microwave radiation.
Space dust can also give off signals similar to those interpreted to be gravitational waves, and according to a separate team of researchers, writes McKee, the field of view of the BICEP2 experiment was looking straight through a cloud of supernova dust.
Now that's not to say that the gravitational wave finding is wrong, but just that it could be wrong. And, wrong in a more specific way than the general existential “what if the universe is all a butterfly's dream” way. And, that the odds of it being wrong are not insubstantial. According to McKee, observations from another project should help clear up whether everyone's excitement was just ruined by a bunch of space dust. Those observations should be available in October.
*This post was updated to emphasize that Maggie McKee was the New Scientist reporter covering the study by Liu et al.