New research suggests that not all feeding massive black holes sit stably at the heart of their home galaxies. A team of astronomers has discovered a black hole wandering through its home dwarf galaxy, taking its active region with it. Making this discovery even more remarkable is the fact that this is an intermediate-mass black hole, a type of object that has eluded astronomers for decades.
The discovery that black hole growth may not be limited to galactic centers could shed light on the role supermassive black holes, with masses millions or billions of times that of the sun, play in the evolution of their host galaxies, as well as indicating how these cosmic titans grew so large so rapidly in the early universe.
The off-center accreting black hole, which is blasting out jets as it travels, was discovered in a dwarf galaxy called MaNGA 12772-12704 located around 230 million light-years away. It is positioned around 3,260 light-years from the center of its home galaxy, where scientists would usually expect to find an accreting supermassive black hole dominating a region called an active galactic nucleus (AGN).
“This is like a cosmic lighthouse lit by a wandering black hole,” team member and Shanghai Astronomical Observatory (SHAO) astronomer Liu Yuanqi said in a statement. “Although it has strayed from the galactic center, it still shines outward with powerful energy.”
Black hole wanderers and dwarf galaxies
The commonly accepted picture of galaxies and black holes sees supermassive black holes sitting at the hearts of galactic centers acting as a central engine, sometimes quiet, sometimes gobbling up matter and triggering powerful jets. However, scientists are increasingly discovering that some massive black holes stray from their perches in the center of galaxies. These wandering black holes can then drift to the galactic disks of their home systems or can even make it to the outskirts of these galaxies.
Astronomers hunt these rogue black holes in dwarf galaxies because, when compared to large galaxies, their smaller masses and simpler evolutionary history preserve more clues about the early growth of black holes. It is predicted that when galaxies merge or when multiple bodies interact, a gravitational recoil can result that is capable of launching black holes from the weaker gravitational influence of the centers of dwarf galaxies.
Scientists have also used simulations to demonstrate that many dwarf galaxy black holes could be displaced by as much as 3,000 light-years, but evidence of this has proved elusive.
That was until this team turned its attention to MaNGA 12772-12704 using data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. They discovered weak AGN activity at the heart of this seemingly average dwarf galaxy, but more interestingly, they found strong radio emissions offset from the AGN by around 3,000 light-years.
Following up with the Very Long Baseline Array (VLBA), the team detected temperatures exceeding 1.8 billion degrees Fahrenheit (1 billion degrees Celsius). They also discovered a jet stretching out for 7.2 light-years. These are features usually associated with an AGN inhabited by a feeding supermassive black hole at the heart of a galaxy.
To investigate deeper, the team turned to archival astronomical data collected between 1993 and 2023, finding that this region offset from the center of MaNGA 12772-12704 becomes brighter and then dims over the course of decades. This is characteristic of a supermassive black hole that is accreting matter and growing.
The team was able to ascertain that this off-center feeding black hole currently has a mass of 300,000 times that of the sun. That isn’t great enough to make it a supermassive black hole, but instead puts it in the category of elusive intermediate black holes.
That is exciting in itself because these “middleman” black holes have thus far proved difficult for astronomers to detect. Scientists know they must be out there in great numbers as they should be an important stage in the merger process that sees stellar mass black holes, with masses 10 to 1000 times that of the sun, combining over hundreds of millions of years to create supermassive black holes.
The team’s research confirms that an intermediate-mass black hole located outside the galactic nucleus can also sustain accretion and produce jets just like a supermassive black hole in a central AGN.
This, in turn, suggests that black holes can feed and grow “offsite,” potentially offering an avenue of investigation to discover how early supermassive black holes were able to grow to incredible masses before the universe was even 1 billion years old.
Though rare currently, the next generation of telescopes could uncover many more of these “lost black holes.”
“This discovery prompts us to rethink black hole–galaxy co-evolution. Black holes are not only central ‘engines,’ they may also quietly reshape their host galaxies from the outskirts,” team leader An Tao from the Shanghai Astronomical Observatory of the Chinese Academy of Sciences said.
The team’s research was published on Sept. 4 in the journal Science Bulletin.