X-ray observations have found copious amounts of very hot gas in galaxy clusters, and in the central regions more than was expected. While supernovae and shock excitation will heat the gas, it should cool off and flow back onto the galaxies, yet this is not observed. Astronomers have suggested that some other source continues to heat the gas, and a prime candidate is feedback from the supermassive black holes that make up active galactic nuclei (AGN). X-ray observations have indeed found evidence for disturbed gas that could be caused by AGN jets that generate hot bubbles as they push outward. How the energy from the AGN outburst actually heats the gas is, however, poorly understood.
Harvard-Smithsonian Center For Astrophysics (CfA) astronomers Paul Nulsen and Bill Forman and their colleagues used very sensitive Chandra observations, together with radio images from the new Giant Metrewave Radio Telescope near Pune, India and the Very Large Array in New Mexico, to study an AGN outburst in the local group of galaxies called 3C 88. They were able to detect shocks pumping energy into a hot cavity equivalent to over a billion suns shining for a billion years, the largest amount of such activity known at the center of a cluster. Moreover, the observed AGN jets are not aligned with the shape of the hot cavity. This new result reconfirms that powerful AGN with jets can indeed keep the X-ray gas hot and slow its flow back onto the galaxy cluster. The scientists also argue that in this case the AGN jets have apparently reoriented relatively recently, perhaps in just the past few tens of millions of years.
Reference: “AGN Feedback in Galaxy Group 3C 88: Cavities, Shock, and Jet Reorientation” by Wenhao Liu, Ming Sun, Paul Nulsen, Tracy Clarke, Craig Sarazin, William Forman, Massimo Gaspari, Simona Giacintucci, Dharam Vir Lal and Tim Edge, 24 January 2019, Monthly Notices of the Royal Astronomical Society.