What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?

Krisztina Perger, Judit Fogasy, Sándor Frey

First listed 2025-09-03 | Last updated 2025-09-03

Abstract

The real nature of little red dots (LRDs), a class of very compact galaxies in the early Universe recently discovered by the James Webb Space Telescope, is still poorly understood. The most popular theories competing to interpret the phenomena include active galactic nuclei and enhanced star formation in dusty galaxies. To date, however, neither model gives a completely satisfactory explanation to the population as a whole; thus, alternative theories have arisen, including tidal disruption events (TDEs). By considering observational constraints on the radio emission of LRDs, we discuss whether TDEs are adequate alternatives solving these high-redshift enigmas. We utilise radio flux density upper limits from LRD stacking analyses, TDE peak radio luminosities, and volumetric density estimates. We find that the characteristic values of flux densities and luminosities allow radio-quiet TDEs as the underlying process of LRDs in any case, while the less common radio-loud TDEs are compatible with the model under special constraints only. Considering other factors, such as volumetric density estimates, delayed and long-term radio flares of TDEs, and cosmological time dilation, TDEs appear to be a plausible explanation for LRDs from the radio point of view.

Short digest

The authors test whether little red dots can be explained as tidal disruption events by confronting 3 GHz stacking-based radio non-detections of LRDs with known TDE radio luminosities and volumetric rates. Converting the VLASS/GOODS-N/COSMOS stacking limits into rest-frame specific luminosities across the LRD redshift range, they find radio-quiet TDEs are fully consistent with the limits, while radio-loud TDEs fit only in restricted redshift–spectral-index regions. Forward-modeling fluxes for representative TDEs (RQ: XMMSL1 J0740−85, ASASSN-14li; RL: Sw J1112.82, Sw J2058+05) and comparing number densities shows that delayed, long-lived radio flares plus cosmological time dilation still keep a TDE origin plausible from the radio point of view. The single radio-detected LRD (PRIMER-COS 3866) also lies within the allowed parameter space.

Key figures to inspect

• Figure 1: Map the LRD radio-luminosity space against dashed/dotted contours for RL/RQ TDE exemplars; check where the RL/RQ boundary falls relative to the stacking-based luminosity ceiling and where PRIMER-COS 3866 sits.
• Figure 2: For the two template TDEs (Sw J2058+05 and XMMSL1 J0740−85), read off the predicted 3 GHz fluxes versus redshift and spectral index; note which regions would have been excluded by current VLASS/GOODS-N stacking limits and which remain allowed.
• Figure 3: Compare LRD volumetric densities to galaxy densities and TDE occurrence-rate curves; assess whether plausible TDE rates (RQ vs RL) can supply the observed LRD numbers as a function of redshift.
• Table 1 (implied in text): Note the adopted peak radio luminosities and redshifts of the four comparison TDEs; these anchor the RL/RQ contours used in Figures 1–2.
• PRIMER-COS 3866 reference lines (in Figs. 1–2): Verify how the lone radio detection compares to the RL/RQ threshold and stacking limits, testing consistency with an RQ-TDE interpretation.