Can molecular clouds live long?

TL;DR

This paper argues that some molecular clouds, especially in outer galaxy regions, may survive longer than the traditionally accepted 30 million years, due to factors like the rarity of massive star formation and delayed star formation onset.

Contribution

It presents evidence that a significant fraction of molecular clouds can persist for over 100 million years, challenging the standard disruption timescale assumption.

Findings

Some molecular clouds may last over 100 million years.

Long-lived clouds are linked to the absence or delay of massive star formation.

Dark, magnetized gas phases may precede starless giant molecular clouds.

Abstract

It is generally accepted that the lifetime of molecular clouds does not exceed $3\cdot 10^7$ yr due to disruption by stellar feedback. We put together some arguments giving evidence that a substantial fraction of molecular clouds (primarily in the outer regions of a disc) may avoid destruction process for at least $10^8$ yr or even longer. A molecular cloud can live long if massive stars are rare or absent. Massive stars capable to destroy a cloud may not form for a long time if a cloud is low massive, or stellar initial mass function is top-light, or if there is a delay of the beginning of active star formation. A long duration of the inactive phase of clouds may be reconciled with the low amount of the observed starless giant molecular clouds if to propose that they were preceded by slowly contraction phase of the magnetized dark gas, non-detected in CO-lines.