Welcome to my first attempt at writing a blog! For the next 5-6 weeks, I’ll be traveling in Antarctica as part of my graduate school research. I will be posting about my adventures here, either as they happen or (if the internet at Pole doesn’t cooperate) after the fact. In the event of slow internet, pictures may be added after I return to the United States.
My group has operated a series of telescopes at the South Pole since long before I started graduate school, all with the same goal: to detect a signal from the very early Universe that will help us learn more about what happened in the first fraction of a second after the Big Bang. Our current experiment is called the Keck Array, which consists of five telescope receivers that can detect microwave emission. Specifically, we are looking at the cosmic microwave background (CMB), which is the oldest light in the Universe. Left over from a time when the Universe was so hot and dense that it glowed, the light from the CMB has been traveling for over 13 billion years to reach us. Two of the Keck receivers observe the CMB at 100 GHz and the other three observe at 150 GHz. (If the Keck Array could see visible light instead of microwaves, we might say that two of the receivers see only “red” light and three see only “green” light.) This year we are also deploying an entirely new experiment, BICEP3. BICEP3 is a single large receiver that has as many detectors as the five Keck receivers combined. It will observe only at 100 GHz.
Earlier this year, our group published a paper where we announced that BICEP2 (the predecessor to the Keck Array) had detected B-mode polarization in the cosmic microwave background at degree angular scales. (If that doesn’t mean anything to you, don’t worry — I’ll put up a post later where I explain the science in more detail.) This observation seemed to match the signal we were looking for — it had exactly the shape that we would expect if the signal originated in the early Universe and, at the time, the signal seemed too strong to be (fully) explained by any other known mechanism. However, since then the Planck satellite, a European mission that observed the polarization of the CMB at seven different frequencies, has revealed new information about the dust in our own galaxy. It was known that the dust in the Milky Way was polarized and could also produce a B-mode polarization signal, but the level of polarization was thought to be low. Planck showed that in some regions of the sky, dust is more strongly polarized than anyone expected. We chose to observe a region that contains very little dust, but if the dust in our part of the sky is as strongly polarized as Planck predicts it could be, then it is possible that the signal we saw could be entirely due to dust. At the time of this posting, no one has published results that definitively answer the question of how much polarized dust is in our field — the Planck data alone show that our field contains some dust, but are too noisy to rule out a CMB contribution entirely.
With this new complication, the field of CMB observations is now rushing to answer the million dollar question: is the signal we saw from the early Universe, local galactic dust, or some combination of the two? To find out, we need to observe the sky at multiple frequencies. The CMB has a fairly constant brightness at microwave frequencies, while dust is brighter at higher frequencies. BICEP2 observed only at 15o GHz, so if we don’t know exactly how bright each component should be then we can’t determine how much of our signal is CMB and how much is dust using the BICEP2 signal alone. But if we look at a higher frequency and see that our signal gets brighter, then we know that we must be looking at dust. If the signal brightness doesn’t change, then we must be looking at only CMB. Along with other members of our group and the Planck team, I have been working on a project to combine all of the available data from BICEP2, Keck, and Planck to figure out what combination of dust and CMB is most likely given the data we have. The results of this analysis will be published soon.
The Keck Array already observes at two frequencies (150 GHz and 100 GHz), but since dust gets fainter at lower frequencies we will be able to see it better if we look at a higher frequency instead. Thus, the plan for this year’s South Pole season is to remove the 150 GHz focal planes from one or two Keck receivers and replace them with new focal planes containing detectors that can observe the sky at 220 GHz. (Going back to the visible light analogy, this is like adding a camera that can see “blue” light to the existing “red” and “green” images.) These new detectors will allow us to make a detailed map of the dust in our field. With this new data, we hope to finally conclusively determine how much of the signal in our field is dust, and how much might be the signal from the early Universe that we hope to find.
Once I get to the South Pole, I will be helping to install the new 220 GHz focal planes in the Keck receivers. I will also help with the many miscellaneous tasks that must be completed to ensure that next year is a successful season. This includes everything from improving our ability to monitor background radio emission from the South Pole Station and orbiting satellites (which could interfere with our observations), to helping get BICEP3 up and running, to shoveling snow. I will use this blog to describe both the work I’m doing and my experiences traveling in Antarctica and living at the South Pole.