Forty-seven hidden galaxies reveal how much of the Universe we may still be missing

Astronomers have uncovered 47 faint dwarf galaxy candidates surrounding three much larger galaxies, revealing a population of elusive stellar systems that had remained almost entirely invisible to previous observations. Only four of these objects had been reported before, meaning that 43 are newly identified candidates. The discovery, made using exceptionally deep optical observations, raises important questions about the completeness of galactic surveys and offers a new opportunity to investigate one of the enduring problems of modern cosmology: whether the number and distribution of dwarf galaxies agree with predictions based on dark matter. The research, led by Crescenzo Tortora of the Italian National Institute for Astrophysics (INAF), was published in the peer-reviewed journal Astronomy & Astrophysics in 2026.

An almost invisible population of galaxies

The newly identified objects were found in the surroundings of NGC 5068, NGC 5084 and NGC 5087, three galaxies located approximately 17 million, 80 million and 100 million light-years from Earth, respectively. Although these larger systems are readily detectable with astronomical instruments, their much smaller potential companions present an entirely different observational challenge. Dwarf galaxies may contain only a tiny fraction of the stellar mass of the Milky Way, and many distribute their stars across extended regions, producing extremely low surface brightness. Consequently, a galaxy containing millions of stars can remain undetected if its light is sufficiently diffuse and becomes almost indistinguishable from the background sky. This observational limitation is particularly significant beyond the Local Group, where individual stars in distant dwarf galaxies generally cannot be resolved with the instruments used in conventional wide-field surveys. The discovery of so many previously unreported candidates within a relatively limited region demonstrates that existing astronomical catalogs can substantially underestimate the number of faint systems present in particular galactic environments.

The research was conducted using the VLT Survey Telescope (VST), operated by INAF at the European Southern Observatory’s Paranal Observatory in Chile. As part of the VST Survey of Mass Assembly and Structural Hierarchy (VST-SMASH), astronomers examined approximately 2.6 square degrees of the sky using deep observations obtained through three optical filters. The images reached surface-brightness limits of approximately 30 magnitudes per square arcsecond in the deepest bands, making it possible to investigate stellar structures that would be difficult to distinguish in shallower observations. Instead of relying solely on automatic detection software, the researchers employed visual inspection procedures to identify possible dwarf galaxies, subsequently removing contamination from foreground stars and other unwanted signals. The team then analyzed the objects’ colors, dimensions and radial brightness profiles, finding structural characteristics broadly consistent with established dwarf galaxy populations. These measurements support their classification as dwarf galaxy candidates, although additional evidence is necessary before their physical nature and association with the larger galaxies can be definitively established.

Why these galaxies matter for dark matter and cosmology

The scientific importance of this discovery extends well beyond increasing the number of known galaxies. According to the standard cosmological framework, known as Lambda Cold Dark Matter (ΛCDM), the formation of cosmic structures is strongly influenced by the gravitational behavior of dark matter, which provides the underlying framework within which ordinary matter accumulates and galaxies develop. Numerical simulations predict that large galactic halos contain substantial populations of smaller dark matter subhalos, some of which should host observable dwarf satellite galaxies. However, astronomers have historically detected fewer satellites than certain early simulations suggested, a discrepancy widely known as the missing satellites problem. The interpretation has evolved considerably as theoretical models have incorporated more realistic descriptions of star formation, stellar feedback and the suppression of galaxy formation in low-mass halos. Improved observations have also revealed additional faint systems, while comparisons between theoretical predictions and observed populations remain dependent on the assumptions and selection criteria employed. Consequently, the central challenge is not simply to find additional galaxies, but to establish reliable satellite populations and determine whether their abundance, luminosity and spatial distribution agree with physically realistic cosmological models.

The 47 objects identified by VST-SMASH provide a valuable opportunity to investigate this problem beyond the immediate surroundings of the Milky Way and Andromeda. Their projected positions suggest that a substantial fraction could be gravitationally associated with NGC 5068, NGC 5084 or NGC 5087, potentially expanding the known populations of dwarf satellites around these galaxies. Nevertheless, identifying an object near a galaxy in an astronomical image does not establish a genuine physical association, since galaxies located at substantially different distances can appear close together when projected onto the celestial sphere. Spectroscopic observations will therefore be necessary to measure the candidates’ velocities, constrain their distances and establish which systems are genuine satellites rather than unrelated foreground or background objects. Until those measurements are available, the discovery should not be interpreted as a resolution of the missing satellites problem or as evidence that the standard cosmological model has been disproven. Its significance lies in supplying previously unavailable observational evidence that could make future comparisons between simulations and actual galaxy populations considerably more reliable.

A possible connection to the mystery of satellite galaxy planes

The spatial arrangement of the candidates introduces another interesting possibility. Around NGC 5084, their apparent distribution suggests a potentially flattened configuration resembling the satellite structures investigated around the Milky Way and other nearby galaxies. Such arrangements have attracted considerable attention because the three-dimensional positions and orbital motions of satellite galaxies contain information about the gravitational environment and the processes responsible for assembling galactic systems. In some cases, observations have motivated debate over how frequently coherent satellite structures should arise within conventional cosmological simulations. However, the current results cannot establish that the candidates around NGC 5084 occupy a genuine physical plane, much less that they share a coordinated pattern of orbital motion. Confirming such a configuration would require reliable distance measurements and velocity information for individual objects. The possibility nevertheless makes these systems particularly interesting observational targets, because determining their actual spatial distribution could help astronomers examine whether previously reported satellite arrangements are relatively common features of galaxy formation or properties associated with particular environments and assembly histories.

The researchers also investigated the internal properties of the newly identified candidates by measuring how their luminosity and color change from their central regions toward their outskirts. Their brightness profiles can generally be described using Sérsic models with indices below two, consistent with the relatively shallow light distributions commonly observed in dwarf galaxies. The measured colors are also compatible with known dwarf populations, although their central color gradients exhibit considerable variation. Some systems appear redder near their centers and less red toward their outer regions, a pattern that may reflect differences in stellar populations, chemical enrichment and evolutionary history. The authors discuss the compatibility of their preliminary results with formation scenarios involving early gravitational collapse, but photometric measurements alone cannot uniquely determine how these galaxies formed. Stellar age, metallicity, dust and environmental effects can produce overlapping observational signatures, making additional spectroscopic information essential for distinguishing competing explanations. Deeper imaging will also help researchers characterize their faint outskirts and investigate whether gravitational interactions with neighboring galaxies have influenced their structural evolution.

The next observations could transform the galactic census

The discovery illustrates the scientific value of combining exceptionally deep observations with careful analysis of structures that conventional surveys may overlook. The VST’s OmegaCam instrument enabled the team to investigate faint galactic outskirts with sufficient sensitivity to measure their light distributions more accurately than previous, shallower observations. Future observations from the European Space Agency’s Euclid space telescope could substantially expand this investigation, since VST-SMASH was designed to overlap with regions included in Euclid’s observational program. Combining ground-based and space-based measurements should allow astronomers to improve the identification of diffuse systems, refine their structural parameters and potentially uncover additional galaxies that remain below existing detection limits. Nevertheless, the decisive next stage will involve spectroscopy, which is required to determine whether the candidates truly belong to their proposed host systems and to establish reliable satellite counts for comparison with theoretical expectations.

Ultimately, the significance of the VST-SMASH findings lies in what they reveal about the limitations of our astronomical perspective. A substantial population of galaxies can remain unrecognized not because its members lack stars or occupy inaccessible regions of the Universe, but because their light is distributed so thinly that conventional observations fail to distinguish them from the background. The identification of 47 dwarf galaxy candidates, including 43 previously unreported objects, demonstrates how improvements in observational depth can transform our understanding of seemingly familiar regions of the sky. Whether these galaxies will ultimately support existing theoretical predictions, expose shortcomings in particular models or reveal previously unrecognized evolutionary processes remains an open scientific question. Establishing a more complete inventory of these faint stellar systems is essential for understanding how galaxies assemble, how their environments shape their evolution and how dark matter influences the large-scale architecture of the cosmos.

© 2026 Homer Dávila Gutiérrez, FRAS — SKYCR.ORG. All rights reserved. Scientific publication: Crescenzo Tortora et al., VST-SMASH: VST Survey of Mass Assembly and Structural Hierarchy. II. Exploring dwarf galaxies in the vicinity of NGC 5068 and of the two galaxies NGC 5084 and NGC 5087 at the edges of the Virgo Supercluster. Astronomy & Astrophysics, 713, A152 (2026). DOI: 10.1051/0004-6361/202558634 .