  Initially conceived for entertainment, social media platforms have profoundly
transformed the dissemination of information and consequently reshaped the
dynamics of agenda-setting. In this scenario, understanding the factors that
capture audience attention and drive viral content is crucial. Employing
Gibrat's Law, which posits that an entity's growth rate is unrelated to its
size, we examine the engagement growth dynamics of news outlets on social
media. Our analysis encloses the Facebook historical data of over a thousand
news outlets, encompassing approximately 57 million posts in four European
languages from 2008 to the end of 2022. We discover universal growth dynamics
according to which news virality is independent of the traditional size or
engagement with the outlet. Moreover, our analysis reveals a significant
long-term impact of news source reliability on engagement growth, with
engagement induced by unreliable sources decreasing over time. We conclude the
paper by presenting a statistical model replicating the observed growth
dynamics.
