Those Elusive Gravitational Waves Stay That Way
milky way galaxy

A team of researchers were the center of a big story last year when they announced they had discovered what appeared to be evidence of primordial gravitational waves.

Using the BICEP2 telescope and the Keck Array, the scientists looked at a piece of the sky between 2010 and 2012. They detected a signal they have never seen before. Dubbed ‘curly B-modes,’ the team believed the signal came from primordial gravitational waves.

Turns out there’s another, less-interesting origin to the signal. Interstellar dust.

Scientist have been on the hunt for this signal of cosmic ‘inflation’ for years. According to the prevailing theory, the Universe experienced a sudden expansion that occurred when it was just a fraction of a second old.

A National Science Foundation press release explains the signature and where it is found.

This signature would be seeded by gravitational waves, tiny perturbations in the fabric of space-time, that astronomers believe would have been generated during the inflationary phase.

Interestingly, these perturbations should leave an imprint on another feature of the cosmic background: its polarization.

Interstellar dust also emits polarized light and caused the mix-up.

“When we first detected this signal in our data, we relied on models for Galactic dust emission that were available at the time,” says John Kovac, a BICEP2 principal investigator at Harvard University.

“These seemed to indicate that the region of the sky chosen for our observations had dust polarization much lower than the detected signal.”

The team of scientists knew there was a problem after new data from ESA’s Planck satellite was released in September 2014. The new data showed polarized emission from interstellar dust is ‘significant’ over the entire sky.

The folks running the Planck satellite and the BICEP2 worked together to figure out what the BICEP2 team discovered.

“This joint work has shown that the detection of primordial B-modes is no longer robust once the emission from Galactic dust is removed,” says Jean-Loup Puget, principal investigator of the HFI instrument on Planck.

“So, unfortunately, we have not been able to confirm that the signal is an imprint of cosmic inflation.”

While last year’s ‘discovery’ didn’t quite pan out, the search is still on for the elusive gravitational waves.

To help in the hunt for this signal, the Keck Array at the South Pole added a new frequency, 220 GHz. This should help the telescope better separate the interstellar dust from the gravitational waves it is trying to detect. A new telescope, the BICEP3, has also been commissioned.

At least now scientists won’t be fooled by dust again.

Image credit: NASA

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