Exploring the Birth of Starlight: NASA's Webb Telescope Hunts for Cosmic Dawn

NASA's James Webb Space Telescope is poised to uncover the universe's Cosmic Dawn

NASA's James Webb Space Telescope is poised to uncover the universe's Cosmic Dawn, the moment when the universe was first bathed in starlight. This is according to astronomer Richard Ellis, who is a renowned professor of astrophysics at University College London and author of "When Galaxies Were Born: The Quest for Cosmic Dawn." 

Throughout his six-decade-long career, Ellis has made significant contributions to the field of galactic astronomy and has spent nearly 800 nights at some of the world's best ground-based optical observatories. He has also seen the lookback times for the start of galaxy formation being pushed back to just a few hundred million years after the Big Bang. 

The James Webb Space Telescope is already revolutionizing our understanding of the early cosmos. According to Ellis, in the first six months of operation, the telescope has explored previously uncharted periods of cosmic history and discovered that these early objects appear to be fundamentally different from the galaxies that we observe at later times. These early galaxies are more compact, super-luminous, and form stars at a rate of at least 10 times faster than our Milky Way Galaxy. 

The brightness of these early galaxies is likely due to their low levels of heavy elements, which would result in more massive, brighter stars that burn out quickly, in just 5-10 million years. Yet, surprisingly, these galaxies are only 2-3 thousand light-years across, compared to the diameter of the Milky Way Galaxy, which spans 100,000 light-years. 

As a 6.5-meter infrared telescope with an onboard spectrograph, the James Webb Space Telescope is able to discover and characterize galaxies further back in time than NASA's Hubble Space Telescope. Ellis noted that scientists are now witnessing galaxies that formed just 250-350 million years after the Big Bang, a period beyond the reach of the Hubble. 

To determine the distance to these far-off galaxies, scientists use two key methods: optical photometry to measure the galaxy's color and ground- or space-based spectroscopy to measure a target galaxy's atomic emission and absorption chemical spectra. 

The search for pristine early galaxies, which have yet to be polluted by nucleosynthesis, is like searching for a needle in a haystack, according to Ellis. He believes that the best way to prove the existence of such a galaxy would be to find a spectrum devoid of emission lines other than hydrogen and helium. In the absence of such proof, he and his colleagues may have to resort to statistical analysis to infer the precise timeframe in which these theoretical pristine galaxies saw their first starlight. 

The study of these earliest galaxies is crucial for our understanding of the universe as a whole. It sheds light on the growth of structure in the universe and the birth of starlight, chemistry, and the elements that make up everyday life. Understanding the pace of these events is the final missing piece in the cosmic history puzzle, according to Ellis.