The impact of X-rays on dust in protoplanetary disks

Séminaire IPAG de Lisseth Gavilan (LATMOS), jeudi 23 novembre 2017 à 11h00, salle Manuel Forestini IPAG

Planets form in protoplanetary disks following a long process where icy dust grains collide and stick. The evolution of dust is integrated in the evolution of the star and disk, a complex system where radiative, dynamic and chemical processes intertwine. One of the critical drivers of disk evolution may be the vigorous X-ray emission of young stars, which irradiate their circumstellar disks. Chemical disk models have recently applied X-ray photochemical rates to the gas phase, but the impact of X-rays on disk solids is much less constrained.

To address this issue, we explore the effect of X-rays on protoplanetary dust via laboratory experiments. We begin by the synthesis of laboratory analogs of interstellar dust : silicate and organic nanomaterials. To simulate a classical T Tauri X-ray spectrum, we use synchrotron radiation.

We recently showed that hard X-rays lead to the amorphization of crystalline silicate nanograins, but only when these are admixed with organics [1]. Such effect signals that heterogeneous dust grains evolve in synergy under ionizing radiation. It also demonstrates that X-rays alone can modify the structure of dust grains. We then irradiated organic dust analogs with soft X-rays, and found out that the X-irradiated regions presented drastically enhanced D/H ratios [2]. Our experiments show that X-rays could impact the earliest stages of planet formation and leave radiative imprints in solids during the protoplanetary stage.