Towards understanding physical origin of 2175 Å extinction bump in interstellar medium

The 2175 Å ultraviolet (UV) extinction bump in interstellar medium (ISM) of the Milky Way was discovered in 1965. After intensive exploration of more than a half century, however, its exact origin still remains a big conundrum that is being debated. Here, we propose a mixture model by which the extinction bump in ISM is argued possibly relevant to the clusters of hydrogenated T-carbon (HTC) molecules (C₄₀H₁₆) that have intrinsically a sharp absorption peak at the wavelength 2175 Å. By linearly combining the calculated absorption spectra of HTC mixtures, graphite, MgSiO₃, and Fe₂SiO₄, we show that the UV extinction curves of optional six stars can be nicely fitted. This work poses an alternative explanation towards understanding the physical origin of the 2175 Å extinction bump in ISM of the Milky Way.