An article published in “The Astrophysical Journal” reports a study on a supermassive black hole in the galaxy cluster SPT-CLJ0528-5300 or simply SPT-0528 that had a really extraordinary outburst. A team of researchers used in particular NASA’s Chandra X-ray Observatory to study that activity finding that the materials pushed away created two huge cavities 180° from each other. By measuring the volume and pressure of the displaced gas and calculating the age of the cavities, it was possible to estimate the energy of that activity in over 10<sup>54</sup> joules, the highest discovered so far in a distant cluster. It could be the cause of a limited star formation in clusters like this one.
Supermassive black holes can be very active when they’re surrounded by large amounts of materials that are generally swallowed slowly but sometimes in big “meals”. When this happens, the materials that approach the black hole heat up considerably emitting strong electromagnetic radiation in what’s called the active galactic nucleus (AGN). Part of those materials is ejected in two jets at the black hole’s poles that generate further activity because their speed approaches the speed of light. A particularly energetic active galactic nucleus can influence not only its host galaxy but also its neighbors that are part of the same galaxy cluster.
About 6.7 billion light years away from Earth, SPT-0528 is a galaxy cluster influenced by the supermassive black hole hosted by the galaxy at its center. In that case, the jets of materials created two huge cavities at 180° from each other during an outburst period. These truly extreme objects, which in certain cases can have masses billions of times the Sun’s, may have periods in which they devour the gas that surrounds them and other periods of violent activity in which they behave like the one object of this study. Michael Calzadilla of MIT, one of the authors of this study, called it an extreme activity.
The observations of the galaxy cluster SPT-0528 were conducted in particular with the Chandra X-ray Observatory but radio waves from the supermassive black hole were detected in 2015 and 2016 by the ATCA (Australia Telescope Compact Array) radio telescope. The data collected in particular on the cluster’s central galaxy, the one that contains the active galactic nucleus, made it possible to calculate the energy of that outburst in over 10<sup>54</sup> joules, making it the most powerful of a supermassive black hole observed in a distant galaxy cluster. The image (Courtesy Michael Calzadilla et al. All rights reserved) shows the cavities observed with Chandra at X-rays superimposed on an optical frequency image captured with the Hubble Space Telescope.
Such an activity influences the various galaxies in the cluster SPT-0528, making this type of study interesting to understand its ramifications. Thanks to the latest generation instruments it’s been possible to study the influence of several supermassive black holes but it’s still difficult to understand exactly which activities favor star formation and which inhibit it. According to old theories, the gas in the galaxy clusters cools down and can therefore form many stars, but observations show that the gas in clusters cools down less than expected. The activity of supermassive black holes could prevent gas from cooling down enough to trigger star formation.
Dr. Michael McDonald of MIT, another author of the study, compared this process to a thermostat in which there’s a balance between the gas cooling down in the galaxies and the hot gas released by black holes. Generally this maintains a certain stability in the temperature of the galaxies and even of whole clusters but in SPT-0528 there’s such an activity that the thermostat doesn’t work.
The diverse situations, with different phases of activity observed in different galaxies or galaxy clusters, are helping to understand the evolution processes of galaxies and in particular the influence of supermassive black holes on star formation. SPT-0528 is an extreme case even for active galactic nuclei and for this reason its effects are easier to understand.
