Astronomers using the Australia Telescope Compact Array (ATCA) have detected plasma jets coming from a supermassive black hole in the central galaxy of the Phoenix cluster, a huge group of galaxies located 5.9 billion light-years away in the constellation of Phoenix.
An artist’s impression of plasma jets coming from a supermassive black hole in the central galaxy of the Phoenix cluster. Image credit: NAOJ.
Galaxy clusters contain thousands of galaxies of all ages, shapes and sizes. Typically, they have a mass of about one million billion times the mass of the Sun and form over billions of years as smaller groups of galaxies slowly come together.
At one point in time they were believed to be the largest structures in the Universe — until they were usurped in the 1980s by the discovery of superclusters, which typically contain dozens of galaxy clusters and groups and span hundreds of millions of light-years.
However, clusters do have one thing to cling on to; superclusters are not held together by gravity, so galaxy clusters still retain the title of the biggest structures in the Universe bound by gravity.
“The space between galaxies is not entirely empty. There is very dilute gas throughout a cluster which can be detected by X-ray observations,” said Dr. Takaya Akahori from the National Astronomical Observatory of Japan and colleagues.
“If this intracluster gas cooled, it would condense under its own gravity to form stars at the center of the cluster.”
“However, cooled gas and stars are not usually observed in the hearts of nearby clusters, indicating that some mechanism must be heating the intracluster gas and preventing star formation.”
“One potential candidate for the heat source is jets of high-speed gas accelerated by a supermassive black hole in the central galaxy.”
“The Phoenix cluster is unusual in that it does show signs of dense cooled gas and massive star formation around the central galaxy,” they added.
“This raises the question: Does the central galaxy have black hole jets as well?”
The astronomers used ATCA to search for black-hole jets in the central galaxy of the Phoenix cluster.
They detected diffuse bipolar and bar-shape structures extending from the galaxy’s center.
“These structures correspond to cavities of less dense gas, indicating that they are a pair of bipolar jets emitted by a black hole in the galaxy,” the scientists said.
“Therefore, we discovered the first example, in which intracluster gas cooling and black hole jets co-exist, in the distant Universe.”
The findings appear in the Publications of the Astronomical Society of Japan.
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Takuya Akahori et al. 2020. Discovery of radio jets in the Phoenix galaxy cluster center. Publications of the Astronomical Society of Japan 72 (4): 62; doi: 10.1093/pasj/psaa039
