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Yes. A 2026 study of 2,435 disk-dominated galaxies found that black holes in galaxies classified as bulgeless follow the same relationship between black-hole mass and total stellar mass as the wider disk-galaxy sample. That pattern supports the idea that gradual, non-merger processes can help galaxies and their central black holes grow together. It does not show that mergers never fuel black holes, or prove that every galaxy that looks bulgeless avoided mergers.
What the 2026 study found
Sophie M. Jewell and colleagues analyzed DESI data for 2,435 disk-dominated galaxies that host optical broad-line active galactic nuclei (AGN). An AGN is a bright central region powered by material falling toward a supermassive black hole. Within the sample, the researchers identified 546 bulgeless AGN host galaxies—a sample they describe as at least five times larger than earlier bulgeless-AGN samples.
The paper, “Galaxy-SMBH co-evolution in 2,435 DESI disk galaxies and merger-free BH growth in bulgeless disks,” appeared online on 21 September 2026 in Monthly Notices of the Royal Astronomical Society as an accepted manuscript. The journal describes accepted manuscripts as author-final versions before copyediting and typesetting, so detailed wording or values could change in the final version.
Why the choice of galaxy mass matters
A galaxy’s total stellar mass counts its stars across the whole galaxy. Bulge mass counts stars in its central, rounded component. Those are different ways of describing a galaxy, and the study found different results depending on which one was compared with black-hole mass.
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Black-hole mass versus total stellar mass
The 546 bulgeless hosts follow the same black-hole-mass–total-stellar-mass relation as the broader disk-galaxy sample, with agreement reported within 3σ. In the study’s logarithmic fit for its DESI disk-galaxy sample, the reported slope is 1.00 ± 0.03 and the intercept is −3.7 ± 0.3. These are sample-specific fit values, not a universal formula for every galaxy.
Black-hole mass versus bulge mass
The picture changes when the comparison uses bulge mass: the bulgeless hosts differ from galaxies with bulges in the black-hole-mass–bulge-stellar-mass relation, with disagreement greater than 7σ. That contrast suggests a bulge is not required for a galaxy to lie on the observed black-hole-mass relation when the mass of the entire stellar host is considered.
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What “quiet growth” means—and what it does not
In this context, “secular” growth means growth through non-merger processes. Gas moving within a galaxy can, in principle, reach its central black hole without a galaxy-wide collision. The study supports a significant role for such processes in galaxy–black-hole co-evolution, but its displayed abstract does not measure how much growth comes from any one proposed route, such as gas moving along bars or spiral arms.
The researchers use a bulgeless appearance as an indicator of a relatively quiet merger history. It is a useful clue, not a complete record of a galaxy’s past. A previous Horizon-AGN analysis found that some galaxies that are bulgeless today could have undergone mergers and later rebuilt their disks. It estimated that about one in four present-day bulgeless galaxies in that simulation had experienced a major merger since redshift 2, and about one in three since redshift 3. The same analysis found a pattern broadly consistent with the DESI result: alignment with the black-hole–total-stellar-mass relation and an offset from the black-hole–bulge relation.
Why this does not rule out merger-fueled growth
The DESI result concerns long-term black-hole mass in a selected population of disk galaxies with optical broad-line AGN. Other evidence asks different questions and examines different populations. For example, a 2018 Nature study of obscured luminous black holes found late-stage nuclear mergers in 17.6% of its obscured luminous black-hole sample, compared with 1.1% of a matched inactive-galaxy sample. That is evidence that mergers can be associated with some luminous, obscured episodes; it is not a counter-estimate for the DESI galaxies.
A cosmological simulation offers another kind of comparison, not a direct measurement of the DESI sample. In a 2018 Horizon-AGN study of its modeled present-day massive-galaxy population, about 35% of black-hole mass was attributed directly to mergers—about 22% to major mergers and 13% to minor ones—while about 65% was attributed to secular processes. Those percentages depend on the simulation and its definitions.
The 2026 paper also reports tentative evidence that a control sample of early-type galaxies had higher AGN luminosity than the bulgeless sample, but no statistical difference in black-hole mass. Luminosity describes how bright an AGN is at the time observed; black-hole mass reflects accumulated mass. A difference in brightness is not, by itself, evidence of a difference in total black-hole growth.
How to read the result
- What it supports: black holes can grow alongside disk galaxies without a prominent bulge, and non-merger processes likely contribute substantially to the observed connection between black-hole mass and total stellar mass.
- What it does not establish: that every bulgeless galaxy has been merger-free, that mergers never trigger accretion, or that one specific gas-feeding mechanism explains the result.
- Why the distinction matters: a galaxy’s present shape, its total stellar mass, its bulge mass, its black hole’s accumulated mass, and its current AGN brightness describe related but non-identical things.
Earlier observational work offered precedent: a 2013 Galaxy Zoo/SDSS study presented 13 AGN in massive bulgeless galaxies and argued that black holes could grow substantially without significant mergers. That small sample was not an independent replication of the larger DESI study.
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