Dust in the Ointment

October 18, 2014   |   Reading time: ~3 mins

It’s nice every now and then to have a slight reminder why your work is valuable. At the moment I’m part of a research team, working in the astrophysics department at the University of Exeter,  that are studying dust. I know exactly what you’re thinking, how interesting can dust be? The truth is that interstellar dust is a very complicated topic in modern astrophysics. Not only is it complex but the existence of diffuse dust in space, as well as denser and more complex dust in star forming regions, means that many observations that you make are affected. This is due to the radiation from the objects you’re trying to observe being scattered, absorbed (and polarised) by the intervening dust. Due to this, objects you observe appear both darker and redder. When you’re trying to do really accurate observations this can be a major issue. We’re working to try and improve understanding of this phenomena, to make future observations more accurate. But as I was shown last month, there are plenty more reasons to be studying this stuff.

BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) is an experiment being conducted to measure the polarisation of the CMB (Cosmic Microwave Background). This is being measured to try and find primordial gravitational waves; pretty good evidence of rapid inflation of the very early universe. Back in March this year, a paper was released by the BICEP collaboration that seemed to present very solid evidence of this phenomena, making headlines in the press all over the world. It was a good day for cosmologist everywhere, because it seemed that we’d managed to figure out another piece of the puzzle about what happened instants after the big bang. Enter the Planck collaboration.

A paper released nearly a month ago has cast some doubts upon this startling leap forward for cosmology. The paper in question uses the high frequency instrument on board the Planck spacecraft to measure the polarisation of the cosmic microwave background at high galactic latitudes. One of the main points to glean from this paper is that even in the regions with the faintest dust emission, there’s nowhere that the B-mode polarisation due to primordial gravitational waves could be precisely measured. They analysed the region of the sky that the BICEP2 telescope studied and found out that their polarisation readings due to dust were extraordinarily similar to those BICEP2 had found due to gravitational waves. Essentially, it looks likely that BICEP2 measured the polarisation of the CMB due to dust rather than that of the gravitational waves they were trying to measure.

It’s a relief to see that not even the most consummate of professional scientist isn’t completely infallible and can make mistakes to. It also neatly demonstrates the need for work in my group’s current area of research. Dust may only have small effects most of the time, but on this occasion it may well have shown a false positive for a hotly contested area of research. The good news is that, as far as I know, both teams are now in communication and the next paper should hopefully be a lot more robust for it; a brilliant example of the scientific community in action.


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