The likelihood that a South Pole-based telescope detected elusive gravitational waves earlier this year has just taken another nosedive.
According to a new and highly-anticipated galactic dust map released by the European Planck space telescope today, the region of sky studied by the BICEP2 telescope appears to contain significant quantities of interstellar dust; dust that may be obscuring the primordial light in which BICEP2 apparently detected the signal of gravitational waves. And this is bad news; the possible detection of gravitational waves may have been a false alarm all along.
ANALYSIS: BICEP2 Big Bang ‘Discovery' Team Urges Caution
In a nutshell, last March, astrophysicists led by John Kovac of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., announced the potentially historic discovery that their experiment had, for the first time, detected the signal of gravitational waves etched into the ancient ‘glow' of the Big Bang - a ubiquitous radiation seen at the outermost reaches of the observable Universe known as the cosmic microwave background, or simply CMB.
The discovery of gravitational waves would be historic in itself, but the ramifications of seeing gravitational waves in the CMB would be far-ranging. These gravitational waves would have their origins just after the Big Bang during a rapid period of expansion known as "inflation." This would therefore provide captivating evidence for one of the leading theories of cosmic birth. Also, as the gravitational waves would have been generated when the universe was very tiny, it would raise questions about a quantum gravity origin and provide evidence for the existence of the hypothetical graviton.
In short, the discovery of ancient gravitational waves could tie up some of the most fundamental questions of the quantum and cosmological nature of our Universe.
ANALYSIS: Dust and Rumors: Gravitational Wave Signal Still Legit?
BICEP2 is a very sensitive telescope built with the intent to spot a specific type of polarization theorized to be caused by the presence of gravitational waves in the CMB known as "B-mode polarization." In the March announcement, the excited BICEP2 team were so sure of their findings that they announced the discovery before their results were published in a peer-reviewed journal. Almost immediately, the astronomy community criticized the BICEP2 announcement, suggesting that insufficient consideration for interstellar dust may be interfering with the CMB polarization signal.
Our galaxy is known to be filled with interstellar dust, so any astronomical observations beyond our galaxy have to peer through that dust. Therefore, corrections for the polarizing effects by the dust needs to be made. Planck, which was launched to the Earth-sun L2 point (in the Earth's shadow) in 2009, has been gradually surveying the whole sky in an effort to map the dust so its effects can be better understood.
Although the BICEP2 team contested that they did take the dusty interference into account before the March announcement, the dust data they used as a reference was incomplete and, as it turns out, woefully underestimated the quantity of dust along BICEP2′s line of sight.
ANALYSIS: Big Bang, Inflation, Gravitational Waves: What It Means
In the long-awaited Planck dust maps described today in a paper published by the arXiv preprint service, it appears that although the region of sky studied by BICEP2 is by no means the most dusty part, it is still obscured by a significant quantity of dust - certainly enough to interfere with any CMB signal.
"The level of dust in the BICEP2 region is clearly significant, and also higher than pre-Planck estimates," Jamie Bock, of NASA's Jet Propulsion Laboratory and BICEP2 team member, told Nature News. According to critics, this new map casts the original BICEP2 results into serious doubt - the majority of the CMB polarization was therefore likely caused by the intervening galactic dust and not gravitational waves. Though there may still indeed be a gravitational wave signal in the BICEP2 results, its effect would be minuscule when compared with this dusty interference.
NEWS: Big Bang's Smoking Gun Found
It is worth noting, however, that the Planck results are not a direct comparison to the BICEP2 data, so this new dust map cannot conclusively say the BICEP2 ‘discovery' was false. Planck observes in radio frequencies of 353 GHz, whereas the BICEP2 signal was detected at 150 GHz.
So what's next? The BICEP2 gravitational wave announcement may have been premature, but it is still the most precise measurement of a possible gravitational wave signal in the CMB. Since July, both science teams have been collaborating on a joint paper that will take the Planck dust data into consideration. Also, we now have a map which highlights regions of low interstellar dust density, providing an un-obscured view of the CMB, so future gravitational wave searches can be more directed.
Hopefully, we're still on the trail to detecting gravitational waves, but as today's announcement has proven, our dust-ridden Milky Way is proving to be a huge challenge to one of the biggest astrophysical questions being asked by modern science.
Source: Nature News