First Stars and Epoch of Reionization
With the emergence of the first stars, the universe was lit up for the first time. This ended 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. Upon the first supernova explosions, the universe was also chemically changed forever. Along with huge amounts of energy, the first elements heavier than hydrogen and helium were added to the pristine universe.
MKI scientists are deeply engaged in searching for the first generations of stars to learn about their properties. Theories of how the very first stars formed – which remain as-yet untested – suggest that these objects may have looked very different from the familiar ones that can be seen in the sky today. These distant ancestors would have been on average much brighter and more massive, containing a primordial chemical mixture.
Their high-energy photons would bring into definition the location of the earliest star clusters and 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 critically depends on the development of novel observational techniques and new instrumentation.
Hydrogen Epoch of Reionization Array
Wide-field radio telescopes are designed to image neutral hydrogen structures from the time during and before the first stars lit up the universe for the first time. This offers a unique opportunity of potentially detecting when the universe underwent a critical transition in the early universe: reionization, when the energetic radiation of the first stars became strong enough to make the universe transparent to light. MKI has supported Prof. Jackie Hewitt and her research group in the construction of several radio telescopes and pathfinders to tackle this study of this important transition. The soon-to-be-completed Hydrogen Epoch of Reionization Array (HERA) in South Africa makes the state-of-the-art facility for their research.
Galaxies and intergalactic matter in the early universe
The galaxies we observe today emerged from gravitational condensation of dark matter and gas in the early universe. Early stars in these proto-galaxies emitted the first starlight that interacted with gaseous matter, and also the first heavy elements formed via nuclear fusion in their cores, which were distributed by supernovae. Prof. Rob Simcoe’s team directly observes these processes using advanced optical and infrared telescopes, including MIT’s 6.5-meter Magellan Observatory in Chile, and the James Webb Space Telescope. The group is very active in developing advanced spectrometers and other instrumentation to facilitate these observations, which probe the early stages of galaxy formation when the universe was just 5% of its present age.
Finding the most metal-poor stars
The ever increasing amounts of data on a billion stars in our Galaxy are aiding in the development of ever more fine-tuned search methods to uncover the oldest, most chemically simplistic (“metal-poor”) stars born in the first generations after the Big Bang. Prof. Anna Frebel and her research group are selecting different types of metal-poor stars for studies of the different nucleosynthesis processes that make up the elements from the periodic table. One day, it may even result in the detection of a long-lived low-mass first star.
Galaxy simulations across cosmic time
Prof. Mark Vogelsberger and his research group are exploring galaxy and structure formation questions. The group is using massive detailed computational simulations that are tying together these observational threads into a coherent early picture of how galaxies first assembled. The computation models can make detailed predictions on the growth of galaxies and their various components like stars, gas and supermassive black holes. Modern simulations make predictions about the structure of the Universe that agree remarkably well with the real Universe. The simulations can then be used to understand the detailed formation processes that occur during galaxy formation.