Abstract

The first stars must have formed from gas consisting of only hydrogen and helium, produced in the Big Bang, with zero contribution from ‘metals’ – those elements heavier than helium that are created at later epochs, by nuclear-burning in the cores of stars. We understand metals to play a critical role at later epochs, in cooling the gas sufficiently that it can collapse to form stars. The first stars must form differently from later generations, in as-yet poorly understood ways. During their lives and deaths, the first stars played a significant role in reionizing the cosmic baryonic material, in particular neutral hydrogen, and creating and then dispersing metals far from the sites of early star formation. Stars less massive than around 80% of the mass of the Sun live for essentially the age of the Universe and their surface chemical abundances reflect conditions in the gas from which they form. Old, low-mass stars in nearby galaxies thus probe early star formation. The first stars are also expected to form black holes of 10 solar masses or more, some of which can seed the growth of the supermassive black holes observed in the local Universe, and some of which may remain as stellar-mass black holes in present-day galaxies, powering ultra-luminous X-ray sources, and produce gravitational waves as binaries. The impact of the first stars on subsequent star formation and galaxy evolution depends on many unknown quantities, including the relative distribution by number of their individual masses (the Initial Mass Function, IMF), the properties of the dark matter halos within which they are predicted to form, their environment – both the immediate surroundings and on larger scales – and how they cluster. These issues form the basis of the proposed meeting, with presentations of new results from observations relevant to the most metal-poor and oldest stars, as well as nearby stellar systems and the chemical enrichment of the intergalactic medium. These observational discoveries will be discussed in the context of the results from theoretical calculations of, for example, star formation in metal-free mostly atomic gas, the IMF of the first stars, stellar evolution of the first stars, the properties of the first collapsed dark-matter halos, along with simulations of their evolution in a cosmological context. The formation of seed black holes from the first stars and possible growth and evolutionary paths to supermassive black holes and active galactic nuclei will also be discussed in one of the sessions.