Abstract
Abstract The search for the first stars formed from metal-free gas in the universe is one of the key issues in astronomy because it relates to many fields, such as the formation of stars and galaxies, the evolution of the universe, and the origin of elements. It is not still clear if metal-free first stars can be found in the present universe. These first stars are thought to exist among extremely metal-poor stars in the halo of our Galaxy. Here we propose a new scenario for the formation of low-mass first stars that have survived until today and observational counterparts in our Galaxy. The first stars in binary systems, consisting of massive- and low-mass stars, are examined using stellar evolution models, simulations of supernova ejecta colliding with low-mass companions, and comparisons with observed data. These first star survivors will be observed as metal-rich halo stars in our Galaxy. We may have identified a candidate star in the observational database where elemental abundances and kinematic data are available. Our models also account for the existence in the literature of several solar-metallicity stars that have space velocities equivalent to the halo population. The proposed scenario demands a new channel of star formation in the early universe and is a supplementary scenario for the origin of the known metal-poor stars.
Highlights
The first stars in the universe draw much attention for the understanding of the star formation history in the early Galaxy
If the separation is small enough, namely ∼< 0.1 au, the companion star can be very metal-rich, it depends on the chemical composition of the yield and how the supernova ejecta mix with the convective envelope of low-mass stars
We have argued that survivors of the first stars can be found among metal-rich stars 30 in the Galactic halo. This is due to the small radii in the first massive stars, which enables them to contaminate low-mass companion stars with supernova ejecta in binary systems
Summary
The ejecta of a supernova explosion in the massive star collide with its low-mass companion, which will either strip away or will be gravitationally confined to the surface of the companion or both may happen due to a wide range of the speed of the ejecta This scenario provides a new pathway to look for evidence of polluted first stars among known halo stars in the Milky Way galaxy, where there are more than 500 stars with detailed chemical abundances derived from high-resolution spectra.
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