First Stars/Reionization, Cosmic Structure

MKI scientists are deeply engaged in searching for the first populations of stars which formed in the early universe. These sources ushered in the end of the cosmic dark age, a period which began around 300 million years after the Big Bang and lasted for 300-500 Million years thereafter. During this time before the first stars, the universe was composed of dark matter, mixed with hydrogen and helium gas, with no stars, galaxies or heavier elements. Theories of how the very first stars form – which remain as-yet untested – suggest that these objects may have looked very different from the familiar ones we see in the sky today. These distant ancestors would have been on average much brighter and more massive, containing a primordial chemical mixture. Their photons would bring into definition the location of early galaxies, and ionize the universe, ushering in the modern era of stars and galaxies.

Because early universe studies probe very faint and distant sources, scientific advancement depends on the development of novel observational techniques and new instrumentation. MKI has supported the construction of new wide-field radio telescopes designed to image neutral hydrogen structures from the time during and before First Light (J. Hewitt, M. Tegmark), and MKI also delivered the FIRE infrared spectrometer to the Magellan telescopes, enabling the direct observation of galaxies and quasars at >95% lookback time to the Big Bang (R. Simcoe). New surveys of the Milky Way’s halo are yielding stars of very low chemical abundance that offer glimpses into how stars form in chemically pristine environments (A. Frebel). And new computational simulations are tying together these observational threads into a coherent early picture of how galaxies first assembled.