much talked about; creating a stir; the talk of the town
Describes a topic, person, or event that is widely discussed and causing public excitement or controversy. Often used in news or social media contexts.
His new song is the talk of the town.
The scandal caused a stir in political circles.
話題 is a general term for 'topic' or 'subject of conversation', while 話題騒然 specifically means that the topic is causing a big stir.
騒然 means 'noisy' or 'uproarious' on its own, but 話題騒然 is a fixed compound meaning 'much talked about'.
Compound of 話題 (topic) and 騒然 (noisy, uproarious). The exact historical derivation is uncertain, but the combination naturally conveys a topic that is causing a commotion.