In our traditional view, black holes are usually thought to “reside” at the centers of galaxies. However, a recent study has discovered a wondering black hole in a dwarf galaxy about 230 million light-years away (redshift z = 0.017). Unlike the norm, this black hole is not located at the galactic center but is offset by nearly one kiloparsec, and it is launching radio jets. This off-nuclear, in-situ accreting black hole with jets—found in a nearby dwarf galaxy—is among the closest and most convincing cases confirmed so far. The discovery strengthens the idea that black hole growth is not limited to galactic centers, offering a new perspective on how supermassive black holes could have grown so rapidly in the early universe.This research was published online in Science Bulletin on September 5, 2025.

Figure 1: Artistic illustration, co-created with ChatGPT

Black Holes Are Not Always in Galactic Centers

In the common picture of the cosmos, black holes are often regarded as the “hearts” of galaxies. Yet increasing observations show that some black holes do not obediently remain at the galactic center. Instead, they are displaced, roaming through the galactic disk or outskirts. Such objects are called wandering black holes, akin to lost travelers drifting across the universe.

Why look for them in dwarf galaxies? Because dwarf galaxies have smaller masses and relatively simpler evolutionary histories, they act as “cosmic fossils” that preserve clues about early black hole growth. Theory predicts that gravitational recoil after galaxy mergers, or interactions involving multiple bodies, can easily kick black holes out of the shallow gravitational wells of dwarf galaxies, leaving them wandering thousands of light-years away. Some simulations even suggest that a considerable fraction of dwarf-galaxy black holes may be displaced by nearly a kiloparsec (~3,000 light-years). Yet for a long time, direct and unambiguous observational evidence has been lacking.

New Discovery: A “Radio-Loud Wandering Black Hole” in a Dwarf Galaxy

An international team led by SeniorResearcherDr. Tao An at the Shanghai Astronomical Observatory, Chinese Academy of Sciences, focused on a dwarf galaxy named MaNGA 12772-12704, located only about 230 million light-years away (z ≈ 0.017) from us. Using integralfield units(IFU) data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, they found that this galaxy exhibits weak active galactic nucleus (AGN) signatures. Although its overall morphology is regular and shows no obvious signs of merging or a double AGN, one key feature stood out: the associated radio emission is offset from the geometric center of the galaxy by nearly one kiloparsec.

To confirm the nature of this source, the team used the Very Long Baseline Array (VLBA) radio telescope to conduct deep imaging at 1.6 GHz and 4.9 GHz. The results revealed that the source lies 2.68 arcseconds away from the galactic center (corresponding to 0.94 kpc), with a radio core brightness temperature exceeding one billion Kelvin. At 1.6 GHz, they detected a jet structure extending about 2.2 parsec (7.2 light-years) southeastward. These are typical features of an AGN.

Furthermore, by analyzing archival data spanning 1993–2023, the team discovered that the source exhibits irregular, long-term variability—becoming brighter and dimmer over decades. This behavior is consistent with sustained, in-situ accretion onto a black hole, and clearly distinct from the monotonically decreasing typical of supernova remnants, effectively ruling out such “impostors.” Based on the stellar mass of the host galaxy, the black hole’s mass is estimated to be about 300,000 times that of the Sun, placing it in the intermediate-mass black hole (IMBH) category.

Bringing together multiple lines of evidence, the team confirmed that this is indeed an actively accreting, off-nuclear black hole with jets—currently the nearest and most robustly confirmed case of its kind. Associate Researcher Dr. Yuanqi Liu vividly compared it to “a cosmic lighthouse lit by a wandering black hole—though it has strayed from the galactic center, it still shines outward with powerful energy.”

Rarity: Why Is This One So Important?

From a broader statistical perspective, this discovery is particularly striking. Among more than 3,000 MaNGA dwarf galaxies, researchers identified 628 AGN candidates, and about 62% of them show evidence of being astrometric offset from the optical centers of their host galaxies. This suggests that off-nuclear phenomena may not be uncommon. However, a “candidate” does not equal a confirmed detection. Dr. Mar Mezcua, as co-author of the paper from Spain's Institute of Space Sciences (ICE-CSIC), highlighted the challenge: ”in dwarf galaxies especially, it is extremely difficult to obtain clear observational evidence for wandering AGN.”

Dr.Tao An’s team conducted multi-stage screening of over 600 candidates, selecting 11 of the most promising targets for radio observations with the highest sensitivity and resolution. In the end, only MaNGA 12772-12704 displayed the “triple solid evidence”: a compact, high-brightness temperature core, parsec-scale radio jets, and long-term variability over 30 years. This makes it the only definitively confirmed case so far.

Scientific Breakthrough: A New Path for Black Hole Growth

The prevailing view has long been that supermassive black holes primarily grow at galactic centers, rapidly feeding on central gas reservoirs. This study, however, demonstrates that an intermediate-mass black hole located outside the galactic nucleus can also sustain accretion and produce jets. This provides direct observational support for the idea of distributed feeding and multi-site growth as a potential pathway for the rapid formation of supermassive black holes in the early universe.As Dr. An notes:"This discovery prompts us to rethink black hole–galaxy co-evolution. Black holes are not only central 'engines' but may also quietly reshape their host galaxies from the outskirts."

Moreover, even when located in a galaxy’s “suburbs”, wandering black holes can still inject energy into the surrounding gas through powerful outflows, influencing galactic dynamics and star formation.

Outlook: Unveiling the Cosmic Population of “Invisible” Black Holes

This study transforms wandering black holes from theoretical speculation into direct observational reality. With the advent of next-generation telescopes, such “lost black holes” may no longer be rare. In the near future, extremely large optical telescopes will measure galactic centers and structures with higher precision. While deep, high-resolution radio surveys using facilities like the FAST core array and Square Kilometre Array (SKA) will detect even fainter radio signals, potentially resolving sub-parsec-scale micro-jets. These advances will bring breakthroughs in confirming and statistically studying off-nuclear black holes.

Perhaps, one day, we will recognize that wandering black holes are not rare at all, but rather silent travelers at the edges of galaxies, quietly shaping their hosts’ cosmic evolution.

Figure 2: Top-left panel: Optical Integral Field Unit (IFU) spectrum.Top-right panel: Corresponding BPT diagnostic diagram for the pixels, which utilizes the ratios of specific emission lines in the galaxy spectrum to distinguish between ionization sources from star formation and active galactic nucleus (AGN) activity.Bottom-left panel: Optical image overlaid with radio contours from the FIRST
survey.Bottom-right panel: The core-jet structure observed by the Very Long Baseline Array (VLBA) at radio wavelengths.

Researcher Tao An served as the corresponding author, Assistant Researcher Yuanqi Liu was the first author. This research was completed through a collaboration between the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, the Institute of High Energy Physics of the Chinese Academy of Sciences, and multiple research institutions from Spain, Sweden, and the Republic of Korea.The study was supported by projects including the National SKA Program of China, the National Natural Science Foundation of China (NSFC), the Shanghai Oriental TalentsProgram (Leadership Project), the Xinjiang Tianchi Talents Program.

Doi: https://doi.org/10.1016/j.scib.2025.09.001

Contact：

Tao An: antao@shao.ac.cn

Yuanqi Liu: yuanqi@shao.ac.cn