Hsin Cynthia Chiang

Research

As a cosmologist, I study the history and structure of the universe as a whole. How did the universe begin, what is it made of, and how will it evolve? In our current understanding of cosmology, the universe was created 14 billion years ago in a massive explosion called the Big Bang, and all of the structure that is visible today was formed as the universe expanded and cooled. Remarkably, a tiny amount of heat from that initial explosion can still be measured today: if we look anywhere in the sky, we can detect the Big Bang's faint "afterglow," which is known as the cosmic microwave background (CMB). The CMB is essentially a snapshot of the universe in its infancy and is a powerful tool for studying its origins. Just as archaeologists analyze ancient civilizations by examining their remaining artifacts, cosmologists are able to piece together the history of the universe by decoding the faint patterns in the CMB.

The rapid development of telescopes and detector technology has played a key role in transforming cosmology into a precision science. I work on several telescopes that aim to measure the temperature and polarization fluctuations in the CMB with improved sensitivity, allowing us to elucidate the physics of the early universe. Most recently, I spent a year in Antarctica working as a winterover scientist for the South Pole Telescope (SPT), pictured on the left. The SPT is a 10-meter telescope that has been observing the microwave sky since 2006, producing high resolution images of the CMB. An upgraded camera was installed on the telescope in 2012, enabling the instrument to measure polarized light. I spent 10 months at the South Pole during the 2012 Austral winter to troubleshoot the new camera and ensure smooth operation of SPT. During the winter season, the South Pole station is completely isolated as airplanes are unable to land in the total darkness and extreme cold.

 

Before my winter at the South Pole, I was a postdoc at Princeton working with Bill Jones's group. One of the experiments that I joined is SPIDER, a balloon-borne telescope that aims to test the theory of Inflation, a period of accelerated expansion of the universe that is believed to have occurred within the first 10-34 second after the Big Bang. One prediction of Inflation is the existence of a gravitational wave background that imparts a unique imprint on the CMB by introducing a minuscule "curl" pattern in the polarization. This polarization pattern has not yet been observed, and a detection would provide powerful confirmation of Inflationary theory. SPIDER will search for the curl signature by measuring CMB polarization with high fidelity over 10% of the sky that is exceptionally clean of Galactic foregrounds. The experiment is scheduled to launch from McMurdo station at the end of 2013 and will circumnavigate Antarctica in a 20-30 day flight. As illustrated in the photo on the right, the instrument consists of six independent telescopes bundled into a 1000-liter liquid helium cryostat. The multiple telescopes not only achieve high sensitivity, but they also provide redundancy for internal consistency checks.

 

While at Princeton, I also joined the Planck consortium and became a member of the High Frequency Instrument (HFI) core team. Planck is a satellite that mapped the microwave sky between August 2009 and January 2012, producing a total of four all-sky surveys. The image on the left (credit: planck.fr) shows an artist's rendering of Planck in orbit at L2. The HFI is one of two instruments on board, and the detectors are distributed over 100-857 GHz in six frequency bands, the lowest four of which have polarization capability. Planck's multifrequency, high-resolution, full-sky temperature and polarization maps will be a spectacular data set not only for cosmology, but also a wide variety of astrophysical studies. The initial in-flight performance and several astrophysical results have already been published, and these are only the beginning of a wealth of forthcoming analyses.

 

I did my graduate work between 2002 and 2008 at the California Institute of Technology, where I was a member of Andrew Lange's research group. My thesis experiment was BICEP, a ground-based microwave telescope that was specifically optimized to constrain Inflationary gravitational waves by measuring CMB polarization at degree angular scales. BICEP observed for three years (2006-2008) from the South Pole, and I was involved in the hardware integration, testing, and deployment, both at Caltech and at the Pole. The rightmost photo (credit: S. Richter) shows BICEP at its home, peering out of the roof of the Dark Sector Laboratory. My main contribution to BICEP was the analysis of the first two seasons of CMB data, which provided the most stringent upper limits on the polarization curl pattern.