Observation of the new emission line at ~3.5 keV in X-ray spectra of galaxies and galaxy clusters

TL;DR

This paper reviews the detection of a mysterious 3.5 keV emission line in X-ray spectra of galaxies and clusters, discussing its potential link to dark matter and future research directions.

Contribution

It provides an up-to-date summary of the 3.5 keV line detection, interpretations, and its possible connection to decaying dark matter, highlighting future research paths.

Findings

Detection of a 3.5 keV emission line in galaxy and cluster spectra

Possible interpretation as radiatively decaying dark matter

Summary of current status and future research directions

Abstract

The detection of an unidentified emission line in X-ray spectra of cosmic objects would be a 'smoking gun' signature for particle physics beyond the Standard Model. More than a decade of its extensive searches results in several narrow faint emission lines reported at 3.5, 8.7, 9.4 and 10.1 keV. The most promising of them is the emission line at ~3.5 keV reported in spectra of several nearby galaxies and galaxy clusters. Here I summarize its up-to-date status, overview its possible interpretations, including an intriguing connection with radiatively decaying dark matter, and outline future directions for its studies.