Diffuse interstellar bands

Starlight loses some wavelengths as it passes through material between stars. A molecule can absorb particular wavelengths, leaving a pattern in the light. Which molecules produce the patterns that remain unidentified?[1] [3]

Which molecules carry the unassigned diffuse interstellar bands? An absorption spectrum records wavelengths removed from background starlight. A proposed carrier must reproduce a set of bands and their shapes under relevant conditions, while remaining consistent with how the features change between environments.

A concrete success is the 2015 gas-phase laboratory assignment of two near-infrared bands to C60+, a fullerene molecule missing one electron. The measurements supplied matching band positions and widths. That result resolves particular assignments; it does not identify the much larger remaining population.[1] [3]

Laboratory measurements have identified some patterns with an ionized form of the carbon molecule C60. Most carriers remain unidentified. Knowing a likely charge or molecular family still leaves many possible ingredients.[1] [2] [3]

The 2026 study of the 862.1-nanometre band follows its strength through 12 nearby clouds. Ultraviolet light, cloud density and structure affect the abundance predicted by photoionization models. A rising trend in part of Taurus is consistent with a positively charged carrier, and the authors estimate an ionization-energy constraint.

Those observations narrow physical properties without naming a unique molecule. Secure assignments still need compatible laboratory spectra and environmental behavior. The molecular candidates and astronomical measurements should explain one another, rather than rest on an isolated wavelength coincidence.[2] [3]

These patterns are evidence of chemistry in the space between stars. Identifying the molecules would turn unexplained features in starlight into information about what is there and how those ingredients change between stellar and star-forming environments.[3]

Identified carriers would make the absorption features chemical tracers. Their changing strengths could be related to specific molecules surviving, being ionized or being transformed in different interstellar environments.

This matters to the wider story of carbon between stellar death and new star formation. The 2022 assessment describes abundant carbon-bearing material whose exact molecular identities and transformations remain incomplete. Naming the carriers would add physical ingredients to that story instead of leaving the observed bands as anonymous features.[3]