X-ray Evolution of Young Stars: Early Dimming and Coronal Softening in Solar-Mass Stars with Implications for Planetary Atmospheres

TL;DR

This study tracks how X-ray emissions from young solar-mass stars decrease and soften over the first 750 million years, revealing impacts on planetary atmospheres and habitability.

Contribution

It extends the empirical analysis of X-ray activity evolution in young stars up to 750 Myr, highlighting a faster decline and coronal softening in solar-mass stars than previously modeled.

Findings

Solar-mass stars show rapid X-ray luminosity decline by ~100 Myr.

Coronal softening and disappearance of hot plasma occur in solar-mass stars.

Revised trends suggest lower atmospheric mass loss and altered chemical environments for planets.

Abstract

X-ray and ultraviolet (XUV) emission from young stars plays a critical role in shaping the evolution of planetary atmospheres and the conditions for habitability. To assess the long-term impact of high-energy stellar radiation, it is essential to empirically trace how X-ray luminosities and spectral hardness evolve during the first ~<1 Gyr, when atmospheric loss and chemical processing are most active. This study extends the X-ray activity-mass-age analysis of <25 Myr stars by Getman et al. (2022) to ages up to 750 Myr, using Gaia-based cluster memberships, new Chandra observations of five rich open clusters (~45--100 Myr), and archival ROSAT and Chandra data for three older clusters (~220--750 Myr). We find a mass-dependent decay in X-ray luminosity: solar-mass stars undergo a far more rapid and sustained decline, accompanied by coronal softening and the disappearance of hot plasma by ~100 Myr, compared to their lower-mass siblings. These trends in solar-mass stars are likely linked to reduced magnetic dynamo efficiency and diminished ability to sustain large-scale, high-temperature coronal structures. The trends are significantly stronger than predicted by widely used XUV-rotation-age relations. The revised trends imply systematically lower rates of atmospheric mass loss and water photolysis, as well as altered ionization environments and chemical pathways relevant to the formation of prebiotic molecules, for planets in close orbits around solar analogs. These effects persist throughout at least the ~<750 Myr interval probed in this study.