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James Webb Space Telescope
The End of the Dark Ages: First Light and Reionization

First Light (after the Big Bang)

Theory and observation have given us a simple picture of the early universe. The Big Bang produced (in decreasing order of present mass-energy density): dark energy (the cosmic acceleration force), dark matter, hydrogen, helium, cosmic microwave and neutrino background radiation, and trace quantities of lithium, beryllium, and boron. As the universe expanded and cooled, some hydrogen molecules were formed, and these in turn enabled the formation of the first individual stars. The first stars formed in those regions that were the most dense. According to theory and the Wilkinson Microwave Anisotropy Probe (WMAP), the universe has expanded by a factor of 20 since that time, the mean density was 8000 times greater than it is now, and the age was about 180 million years. Also according to theory, these first stars were 30 to 1000 times as massive as the Sun and millions of times as bright and burned for only a few million years before meeting a violent end. Each one would produce either a (superluminous) pair-instability supernova or collapse directly to a black hole. The supernovae would enrich the surrounding gas with the chemical elements produced in their interiors, and future generations of stars would all contain these heavier elements (“metals”). The black holes would start to swallow gas and other stars to become mini-quasars, growing and merging to become the huge black holes now found at the centers of nearly all galaxies. The distinction is important because only the supernovae return heavy elements to the gas. The supernovae and the mini-quasars, if beamed, should be observable by the JWST. Both might also be sources of gamma ray bursts and gravity wave bursts that could be discovered by other observatories and then observed in followup by JWST. In addition to the supernovae of the first light stars, JWST will also be able to detect the first galaxies and star clusters.

The JWST First Light theme science goal is to find and understand these predicted first light objects. To find them, the JWST must provide exceptional imaging capabilities in the near IR band. To verify that the high-z galaxies are indeed made of primordial stars and do not contain older stellar populations, mid-infrared observations are required. An observational approach to identify these objects has been described in the JWST SWG First Light white paper.