  The emergence of new public forums in the shape of online social media has
introduced unprecedented challenges to public discourse, including
polarization, misinformation, and the emergence of echo chambers. While
existing research has extensively studied the behavior of active users within
echo chambers, little attention has been given to the hidden audience, also
known as lurkers, who passively consume content without actively engaging. This
study aims to estimate the share of the hidden audience and investigate their
interplay with the echo chamber effect. Using Twitter as a case study, we
analyze a polarized political debate to understand the engagement patterns and
factors influencing the hidden audience's presence. Our findings reveal a
relevant fraction of users that consume content without active interaction,
which underscores the importance of considering their presence in online
debates. Notably, our results indicate that the engagement of the hidden
audience is primarily influenced by factors such as the reliability of media
sources mentioned in tweets rather than the ideological stance of the user that
produced the content. These findings highlight the need for a comprehensive
understanding of the hidden audience's role in online debates and how they may
influence public opinion.
