Ground Telescopes Detect 13-Billion-Year Cosmic Dawn Signal

Scientists have, for the first time, used ground-based telescopes to observe polarized microwave light from over 13 billion years ago, revealing how the universe's first stars affected the light left over from the Big Bang during the mysterious 'Cosmic Dawn' epoch. This breakthrough was achieved by the Cosmology Large Angular Scale Surveyor (CLASS) array in Chile's Andes mountains, overcoming significant technological challenges related to the faintness of the cosmic microwave background (CMB) and interference from Earth's atmosphere. Previously, such observations were only possible with space-based missions like NASA's WMAP and ESA's Planck. The faint microwave signals measured by CLASS offer new insight into the period when the universe transitioned from an opaque state to transparency, allowing light to travel freely. These findings, led by teams from Johns Hopkins University and the University of Chicago and published in The Astrophysical Journal, advance our understanding of how the first stars reionized the universe and left unique imprints on the CMB. By comparing CLASS data with space telescope results, researchers have been able to identify and account for terrestrial interference, yielding a clearer view of early cosmic history.