Galaxies gather together through mutual gravitational attraction and form collections known as clusters. The space between galaxies isn’t entirely vacant. There is exceptionally dilute gas all through a bunch that can be identified by X-ray observations.
If this intra-group gas-cooled, it would consolidate under its gravity to form stars at the cluster center. However, cooled gas and stars are not generally seen in nearby clusters’ hearts, demonstrating that some mechanism must be heating the intra-cluster gas and forestalling star formation. One potential contender for the heat source is jets of high-speed gas quickened by a supermassive black hole in the central galaxy.
The Phoenix Cluster is unusual because it shows signs of dense cooled gas and massive star formation around the central galaxy. This raises the question: Does the central galaxy have black hole jets as well?
A team led by Takaya Akahori at the National Astronomical Observatory of Japan used the Australia Telescope Compact Array (ATCA) to search for black hole jets in the Phoenix Galaxy Cluster, the highest resolution to date. They detected matching structures extending out from opposite sides of the central galaxy.
Astronomers detected jets of hot gas blasted out by a black hole in the galaxy at the Phoenix Galaxy Cluster’s heart, located 5.9 billion light-years away in the constellation Phoenix.
Comparing with observations of the region taken from the Chandra X-ray Observatory archive data shows that the structures detected by ATCA correspond to cavities of less dense gas, indicating that they are a pair of bipolar jets emitted by a black hole in the galaxy.
This is the first example in which intra-cluster gas cooling and black hole jets coexist in the distant universe.
Further details of the galaxy and jets could be elucidated through higher-resolution observations with next-generation observational facilities, such as the Square Kilometer Array scheduled to start observations in the late 2020s.
- Takuya Akahori et al. Discovery of radio jets in the Phoenix galaxy cluster center, Publications of the Astronomical Society of Japan (2020). DOI: 10.1093/pasj/psaa039