Supermassive black hole jets stir old cosmic puzzles

Supermassive black hole jets stir old cosmic puzzles

Galaxy clusters are the most massive gravitationally bound systems and encode unique information on the composition of our Universe. They comprise of a massive dark matter halo and up to a few thousand rapidly moving galaxies enveloped by a very hot X-ray emitting plasma, known as the intracluster medium (ICM). Of particular importance for regulating the heating and cooling of the ICM, the decades long “cooling flow” problem, are the relativistic jets produced by supermassive black holes with masses in excess of a billion solar masses. Notwithstanding massive theoretical and observational effort, a major puzzle left to crack is how the energy from these powerful jets is transferred to the ICM to stop the catastrophic cooling.

Figure 1. Panel A shows a volume-rendered image of galaxy cluster and panel B shows the volume-rendered jet material as well as the gas velocity field (arrow vectors) in the cluster center. Panel C shows a cold disc structure which surrounds the SMBH. Finally, panels D and E show a 2D reconstruction of the Voronoi grid used and a velocity streamline map of the lower-right lobe-ICM interface, respectively. Credit: Bourne et al. 2020, MNRAS.

Using the moving-mesh code AREPO, we performed state-of-the-art simulations with the highest-resolution jets to-date within a large scale, fully cosmological cluster environment to shed light on this issue. The simulations make use of a novel refinement technique (see Figure 1) that not only allows high resolution close to the central black hole but also within the jet lobes themselves. We found that the mock X-ray observations of the simulated cluster revealed the so-called “X-ray cavities” and “X-ray bright rims” generated by supermassive black hole-driven jet, which itself is distorted by motions in the cluster remarkably resemble those found in observations of real galaxy clusters (see Figure 2). While it is well accepted that the vast amount of energy injected into the jet lobes (which would be enough to meet the Earth’s power usage for more than 1031 years) is sufficient to offset the cooling losses within the ICM and prevent the formation of a cooling flow, how this energy is effectively and isotopically communicated to the ICM is still an open debate. Our simulations showed that the ICM motions or “weather” are crucial to solving this problem. Through the cluster weather action, the jet lobes can be significantly moved and deformed, stirring them around the cluster, which ultimately leads to jet lobe disruption and effective energy transfer to the ICM which could be the long sought-after solution to combat the “cooling flow” puzzle.

Figure 2. This shows a mock observation made from the simulation on the right and an actual observation of the galaxy cluster MS 0735.6+7421 on the left. Both images show cavities excavated by the lobe inflation surround by X-ray bright rims of dense gas (blue), which are filled by distorted jet material (pink). Credit: Hubble and Chandra Image: NASA, ESA, CXC, STScl, and B. McNamara (University of Waterloo); Very Large Array Telescope Image: NRAO, and L. Birzan and team (Ohio University). Simulated Cluster Image credit: Hubble and Chandra Image (background): NASA, ESA, and B. McNamara (University of Waterloo); Simulated Observation Data: M. A. Bourne (University of Cambridge).

This work has been published in the Monthly Notices of the Royal Astronomical Society: “AGN jet feedback on a moving mesh: lobe energetics and X-ray properties in a realistic cluster environment” by Martin A. Bourne, Debora Sijacki and Ewald Puchwein. Royal Astronomical Society press release: “Stormy cluster weather could unleash black hole power and explain lack of cosmic cooling”, 14 October, 2019.