carbonaceous content of galaxies? There is a phrase in a Science Daily article which appears to be wrong: 

The Milky Way has a very high content of carbonaceous dust, which has been shown to be very rare in other galaxies.

Is there a theory that explains these observations?
From the introduction of the source paper, we can see that what is described is a particular bump in the extinction curve of the galaxy centered at 2175 Ångström (a unit of length used for wavelength). The strength of this bump is large compared to the Large Magellanic Cloud, and is rarer toward the Small Magellanic Cloud.

As mentioned in the comments, the main candidates for the origin of the feature are non-graphitic carbon or polycyclic aromatic hydrocarbons (PAHs). The absence in other environments is attributed to low metallicities or different radiative environments.

Basically, this is a case where we lose information in science reporting. "Very high content of carbonaceous dust" was a translation of a specific strength at a specific wavelength, and "other galaxies" was a translation of surrounding galaxies.

Source:


The 2175 Å extinction feature in the optical afterglow spectrum of GRB 180325A at z=2.25 - Zafar, et al.