A New Probe of the Magnetic Interstellar Medium

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Astronomical research reveals that our universe began with a Big Bang, about 13.7 billion years ago. With modern telescopes we can trace the history of the universe from a few minutes after the Big Bang. But can we explain the Big Bang itself and what gave rise to it? The “Inflationary Theory” attempts to do just that. If Inflationary Theory is correct, then all the structure in the universe, from clusters of galaxies to stars and planets, started as tiny fluctuations in spacetime that were created during the Big Bang. The theory also provides a fascinating link between relativity, which explains the large-scale properties of the universe, and quantum mechanics, which explains the small-scale properties of atoms. Tests of the Inflationary Theory are therefore of fundamental importance to science. According to the Inflationary Theory, there should be a tiny signal in polarized radiation, visible in every direction. The investigators are part of a large international effort to find this faint signal in the Cosmic Microwave Background (CMB). To test the model, the team must accurately measure the polarization from dust clouds in our Milky Way galaxy, which produces a similar kind of faint polarized light. This team has designed and built two revolutionary instruments to measure the polarization of the light from millions of stars. These measurements would enable the team to discriminate polarization due to dust in the Milky Way from that left over from the Big Bang. The investigator will contribute existing education and outreach activities at Cal Tech, including an effort to work with students in the Navajo region, introducing them to radio astronomy. The investigator has developed the Wide-Area Linear Optical Polarimeters (WALOPs), which are based on a novel application of Wollaston prisms. The linear polarization of a star can be measured with a single exposure. This is very important because one needs to measure polarization with accuracy better than 0.1%, and small changes in the atmosphere between successive exposures can cause systematic errors at this level. The team will deploy one of the WALOPs in Crete and the other in South Africa. They will survey the two parts of the celestial sphere that are least contaminated by dust in the Milky Way, around the northern and southern galactic polar caps. This will increase the number of stellar polarization measurements that exist from about 35,000 to over 4 million. They will use the stellar polarization measurements in conjunction with stellar distance measurements to trace the Milky Way magnetic field. The investigators will make major contributions to understanding the structure of the Milky Way’s magnetic fields and determine the effects of Milky Way dust on the polarization signal in the CMB.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.