Discovery of interstellar 1-cyanopyrene: a four-ring polycyclic aromatic hydrocarbon in TMC-1

TL;DR

This study reports the first detection of interstellar 1-cyanopyrene, a four-ring PAH, in TMC-1, revealing its abundance and suggesting its role in the carbon chemistry of star-forming regions and potential origins of solar system materials.

Contribution

The paper presents the discovery of CN-functionalized pyrene in space, providing new insights into interstellar PAH composition and their contribution to planetary system formation.

Findings

Detected 1-cyanopyrene in TMC-1 using the Green Bank Telescope.

Estimated pyrene accounts for up to 0.3% of interstellar carbon.

Suggests interstellar PAHs contribute to the carbon in comets and planetary systems.

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are expected to be the most abundant class of organic molecules in space. Their interstellar lifecycle is not well understood, and progress is hampered by difficulties detecting individual PAH molecules. Here, we present the discovery of CN-functionalized pyrene, a 4-ring PAH, in the dense cloud TMC-1 using the 100-m Green Bank Telescope. We derive an abundance of 1-cyanopyrene of ~1.52 x $10^{12}$ cm$^{-2}$, and from this estimate that the un-substituted pyrene accounts for up to ~0.03-0.3% of the carbon budget in the dense interstellar medium which trace the birth sites of stars and planets. The presence of pyrene in this cold (~10 K) molecular cloud agrees with its recent measurement in asteroid Ryugu where isotopic clumping suggest a cold, interstellar origin. The direct link to the birth site of our solar system is strengthened when we consider the solid state pyrene content in the pre-stellar materials compared to comets, which represent the most pristine material in the solar system. We estimate that solid state pyrene can account for 1% of the carbon within comets carried by this one single organic molecule. The abundance indicates pyrene is an "island of stability" in interstellar PAH chemistry and suggests a potential cold molecular cloud origin of the carbon carried by PAHs that is supplied to forming planetary systems, including habitable worlds such as our own.