The classic scheme of galaxy evolution describes a one-way street: late types (spirals) transform into early types (ellipticals and lenticulars) through mergers and disk instabilities. However, data on recent star formation in early-type galaxies and on 'red nuggets' (compact massive systems at high redshifts) hinted at the possibility of a reverse process. This work stands apart: there is almost nothing nearby, the nearest neighbor is at a distance of 0.586, and no work is directly adjacent. Thematically, it aligns with studies of galaxy mergers, cosmic reionization, and galaxy evolution, but instead of the traditional path from late to early type, it tests the reverse scenario from early to late type using a large spectroscopic survey.
The study uses integral field spectroscopy data from the MaNGA survey (SDSS DR17) for 5124 massive central galaxies with masses ranging from $10^{10}$ to $10^{12}$ solar masses. Morphology is determined from the deep learning catalog of Domínguez Sánchez et al. (2021). In each spiral, regions with suppressed star formation are identified using D4000 index maps (an indicator of stellar population age): if more than 95% of resolution elements within a given radius have D4000 > 1.55, that region is considered a 'quenched central core' (QCC). For 247 such cores with radii larger than 4 arcseconds, radial profiles of age, metallicity, velocity dispersion, and rotation parameter are constructed, along with distribution functions of these quantities for the core and outer disk separately. The core properties are then compared with samples of fully quenched elliptical (1097) and lenticular (264) galaxies.
In 62% of spirals with quenched cores, the D4000 and velocity dispersion distributions are bimodal: the old stellar peak corresponds to the core, and the young peak to the outer disk. Core ages range from $10^9$.6 to $10^9$.8 years, while disk ages range from $10^9$.2 to $10^9$.4 years; core metallicities are close to solar, while disk metallicities are on average 0.2 dex lower. Velocity dispersion in the core is several times higher than in the disk: for 74% of galaxies, the ratio is less than 0.5. At the core boundary, gradients in D4000, age, and velocity dispersion change sharply. The cores follow the same size-mass and velocity dispersion-mass relations as quenched lenticular galaxies: the slope of the dispersion-mass relation for cores is 0.314±0.019, for lenticulars 0.310±0.016, whereas for ellipticals it is 0.233±0.007. Radial profiles of metallicity and rotation in cores also match those of lenticulars. The fraction of slow rotators among cores decreases with mass from 69.2% to 53.2%, similar to lenticulars (from 59.5% to 38.1%), while for ellipticals it increases (from 58.3% to 80.9%). The estimated transformation frequency is that up to ~70% of lenticular galaxies with masses around $10^{10}$.2 solar masses could have become spirals; among the most massive spirals (above $10^{11}$.2 solar masses), up to 55% contain a quenched core.
This work shows for the first time on a large spatially resolved sample that reverse morphological transformation, from lenticular/early-type to spiral, is not an exotic rarity but a common evolutionary path. Unlike neighboring studies that either limited themselves to small volumes (Hon et al. 2022, within 110 Mpc) or studied individual interacting pairs (Yun et al. 2026), this study uses the systematic MaNGA survey with clear criteria for identifying cores and direct comparison of their properties with quenched early-type galaxies. This settles a long-standing question about the fate of 'red nuggets': they do not disappear but instead grow new disks and become the bulges of modern spirals.
The immediate next steps are to search for such cores at higher redshifts to trace their evolution over time, and to perform detailed simulations of gas accretion onto a quenched core, including feedback from an active nucleus. It is important to understand why in some galaxies gas heating by the active nucleus effectively suppresses cooling, while in others it does not. Also to be determined is the role of minor mergers and cold gas inflow from the cosmic web in disk revival.
The results will affect models of galaxy formation, the interpretation of the 'green valley' (the transition zone between blue and red galaxies), and the understanding of quenching mechanisms that halt star formation.
To check how often quenched cores appear in spirals at z~0.5–1, and to link their occurrence with the history of gas accretion from the large-scale structure. To build hydrodynamic simulations that reproduce the two-phase assembly: rapid formation of a hot bulge and slow growth of a cold disk.
An unresolved question in galaxy evolution remains why quenching is reversible and what conditions trigger the 'maintenance mode', where halo heating prevents gas cooling. This work shows that the standard division into star-forming and quiescent based on star formation rate blurs the picture: some 'green' galaxies are moving not toward death but toward revival. This calls for a revision of classification criteria and the inclusion of internal structure when studying quenching.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The study uses MaNGA data for a sample of 5124 massive central galaxies, identifying quiescent central cores (QCCs) in spirals via the D4000 index. For 247 cores, radial profiles were constructed and their properties compared with fully quiescent elliptical and lenticular galaxies. The cores are found to be indistinguishable from lenticular galaxies in size–mass and dispersion–mass relations, metallicity, and the fraction of slow rotators, while the outer disks are young and cold, indicating two separate formation episodes.
Where its strength is
The work quantitatively demonstrates that the central regions of many spiral galaxies match lenticular systems in their properties, providing observational support for the 'rejuvenation' scenario, where a new disk grows around an old bulge.
Where it could go next
Worth trying
Why this may matter
If the reverse evolutionary path (from lenticular to spiral) is indeed common, it would require revising galaxy formation models and their connection to dark matter, and would also change the interpretation of the observed Hubble morphological sequence.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.54, against a usual 0.64. It looks like few have drilled nearby.
The D4000 index is the ratio of fluxes on either side of the break at a wavelength of 4000 angstroms, which arises from the abundance of metal absorption lines in the atmospheres of old stars. In galaxies with active star formation, this break is weak; in 'retired' galaxies, it is deep.
In Isaac Asimov's novel 'The Gods Themselves', an exchange of matter between universes is described that can trigger star formation in quenched systems. The idea of 'revival' of galaxies echoes this image: an external gas reservoir can breathe new life into an old stellar bulge.