Puzzling Phenomenon of Diffuse Interstellar Bands

TL;DR

Diffuse interstellar bands are numerous, diverse absorption features in space with unknown carriers, and despite extensive research, their exact origins remain unidentified, posing a significant challenge for astrophysics.

Contribution

This paper provides a historical overview of DIBs, describes their diversity, and discusses methods to classify them into spectroscopic families, highlighting ongoing challenges.

Findings

No definitive carriers identified for DIBs

DIBs exhibit a wide variety of profiles and intensities

Laboratory spectra matching astrophysical DIBs remain undiscovered

Abstract

The discovery of the first diffuse interstellar bands (DIBs) dates back to the pioneering years of stellar spectroscopy. Today, we know about 300 absorption structures of this kind. There exists a great variety of the profiles and intensities of DIBs, so they can not be readily described, classified or characterized. To the present day no reliable identification of the DIBs' carriers has been found. Many carriers of DIBs have been proposed over the years. They ranged from dust grains to free molecules of different kinds, and to more exotic specimens, like hydrogen negative ion. Unfortunately, none of them is responsible for observed DIBs. Furthermore, it was shown that a single carrier cannot be responsible for all known DIBs. It is hard to estimate how many carriers can participate in producing these bands. The problem is further complicated by the fact that to this day it is still impossible to find any laboratory spectrum of any substance which would match the astrophysical spectra. Here, a historical outline concerning DIBs is followed by a brief description of their whole population. Then, a special attention is focused on the procedures trying to extract spectroscopic families within the set of all known DIBs.