Physical properties of amorphous solid interstellar material from X-ray absorption spectroscopy of Sco X-1

TL;DR

This study uses high-resolution X-ray spectra of Sco X-1 to detect EXAFS signatures, revealing amorphous solid interstellar material with oxygen-oxygen distances similar to water ice, despite water ice's unlikely presence.

Contribution

First detection of EXAFS in interstellar medium using X-ray spectroscopy, indicating amorphous solid structures in diffuse clouds.

Findings

Detected EXAFS signatures in X-ray spectra.

Oxygen-oxygen distances consistent with amorphous water-ice.

Interstellar medium contains amorphous solid material.

Abstract

High quality, high resolution X-ray spectra were obtained of Sco X-1 with the Reflection Grating Spectrometer (RGS) on board the XMM-Newton satellite. The spectrum around the Oxygen K-edge is searched for signatures indicative for EXAFS. Analysis shows a clear indication for the existence of EXAFS with photo-electron scattering distances in the absorbing medium in a range which applies to many solids. When scattering of the photo-electron on Oxygen atoms is assumed, the Oxygen to Oxygen atom distances found are 2.75 Angstrom. This fits with distances as found in amorphous water-ice, although water ice is thought to be an unlikely constituent of the diffuse interstellar clouds which form the absorbing medium towards Sco X-1