CEMP stars: possible hosts to carbon planets in the early universe

TL;DR

This paper investigates the potential for carbon-rich planet formation around ancient, metal-poor stars in the early universe, proposing observational strategies to detect such planets and understand early planetary system formation.

Contribution

It introduces a model linking carbon abundance in CEMP stars to the maximum possible distance for planetesimal formation, and suggests observational methods to detect carbon planets around these stars.

Findings

Maximum planetesimal formation distance depends on [C/H] abundance.

Potential transits of carbon planets are detectable with current/future surveys.

CEMP stars could host early carbon planets, informing early universe planetary formation.

Abstract

We explore the possibility of planet formation in the carbon-rich protoplanetary disks of carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe. The chemically anomalous abundance patterns ([C/Fe] $\geq$ 0.7) in this subset of low-mass stars suggest pollution by primordial core-collapsing supernovae (SNe) ejecta that are particularly rich in carbon dust grains. By comparing the dust-settling timescale in the protoplanetary disks of CEMP stars to the expected disk lifetime (assuming dissipation via photoevaporation), we determine the maximum distance $r_{max}$ from the host CEMP star at which carbon-rich planetesimal formation is possible, as a function of the host star's [C/H] abundance. We then use our linear relation between $r_{max}$ and [C/H], along with the theoretical mass-radius relation derived for a solid, pure carbon planet, to characterize potential planetary transits across host CEMP stars. Given that the related transits are detectable with current and upcoming space-based transit surveys, we suggest initiating an observational program to search for carbon planets around CEMP stars in hopes of shedding light on the question of how early planetary systems may have formed after the Big Bang.