Radio astronomers have discovered jets of hot gas ejected by a black hole into a galaxy at the center of the Phoenix cluster of galaxies. This cluster of galaxies is located 5.9 billion light-years away in the constellation Phoenix. The new discovery, described in the article “Discovery of Radio Jets at the Center of the Phoenix Cluster of Galaxies” in the Publications of the Astronomical Society of Japan, gives astronomers a better understanding of the coevolution of galaxies, gas, and black holes in galaxy clusters.
Galaxies are not randomly distributed in space. Due to mutual gravitational attraction, galaxies come together to form clusters known as clusters. The space between galaxies is not entirely empty. There is a very dilute gas throughout the cluster that can be detected by X-ray observations.
If this intra-cluster gas-cooled, it would condense under its own gravity, forming stars at the center of the cluster. Cooled gas and stars, however, are usually not seen in the hearts of neighboring clusters, indicating that some mechanism must be heating the intracluster gas and preventing star formation. One of the potential candidates for the role of a heat source are jets of high-velocity gas accelerated by a supermassive black hole in the central galaxy.
The Phoenix Cluster is unusual in that it has signs of dense, cooled gas and massive star formation around the central galaxy. The question arises: are there jets of black holes in the central galaxy?
A team led by Taka Akahori of the National Astronomical Observatory of Japan used the Australia Telescope Compact Array (ATCA), the highest resolution to date, to search for jets of black holes in the Phoenix cluster of galaxies. They found corresponding structures extending from opposite sides of the central galaxy. Comparison with observations of the region taken from archived data from the Chandra X-ray Observatory shows that the structures discovered by ATCA correspond to cavities of less dense gas. This means that they are a pair of bipolar jets emitted by a black hole in the galaxy. Thus, the team of scientists discovered the first example in which intra-cluster gas cooling and jets of black holes coexist in a distant universe.
Further details about the galaxy and jets can be sorted out with higher resolution observations using next-generation observing tools such as the Square Kilometer Array. New research and observations are scheduled to begin in the late 2020s.