Early galaxy clusters show surprising heat in infancy.

Astronomers using ALMA detected superheated gas around the forming cluster SPT2349-56 from when the universe was about 1.4 billion years old, using the thermal Sunyaev–Zel'dovich effect. The observation challenges expectations that cluster atmospheres remain cool during the first few billion years.

Astronomers using the Atacama Large Millimetre/submillimetre Array report a direct detection of superheated gas around the forming galaxy cluster SPT2349-56 when the universe was about 1.4 billion years old. The team used the thermal Sunyaev–Zel'dovich effect, which identifies hot gas by the small shadow it casts on the cosmic microwave background. The signal was stronger than expected and was checked over months before being confirmed. The result challenges prior expectations that young clusters should remain relatively cool as they assemble. Key findings: - ALMA observations reveal superheated intracluster gas around SPT2349-56 from a lookback time of about 12 billion years, when the universe was roughly 1.4 billion years old. - The detection used the thermal Sunyaev–Zel'dovich effect, which senses energetic electrons scattering photons from the cosmic microwave background rather than direct gas emission. - The measured intracluster gas appears hotter and more energetic than in many present-day clusters, and the signal was verified over several months. - SPT2349-56 has a compact core about the size of the Milky Way’s halo that hosts more than 30 starburst galaxies and several actively growing supermassive black holes. - The study notes that energetic feedback from black holes and intense star formation could plausibly explain the early overheating and that this pushes the observational record for hot cluster gas earlier than before. Summary: This observation alters expectations about when and how cluster atmospheres heat, leading researchers to reconsider the sequence and speed of cluster evolution. Undetermined at this time.