Simulating galaxy formation (Image credit: Debora Sijacki, Mark Vogelsberger, Lars Hernquist)
Since the Universe is expanding, it must have been denser in the past. But even before we get all the way back to the Big Bang, there must have been a time when stars like our Sun or galaxies like our own Milky Way did not exist because the Universe was denser than these objects are. We therefore face the important question about our origins: how and when did the first stars and galaxies form? Harvard faculty study theoretically the formation of the first galaxies and their environmental impact in terms of the reionization of the intergalactic medium. State-of-the-art numerical simulations are used to predict the formation of stars and black holes within galaxies throughout cosmic history. These predictions will be tested over the upcoming decade through deep observations with the next generation of large-aperture infrared telescopes as well as low-frequency radio mapping of the 21-cm line of hydrogen.