Weighing Little Red Dots with Transient Events

Vinh Tran, Xuejian Shen, Oliver Zier, Anna de Graaff, Rohan P. Naidu, Mark Vogelsberger

First listed 2026-09-02 | Last updated 2026-09-02

Abstract

Short digest

Tran et al. propose using stellar transients to independently weigh Little Red Dots, whose black-hole masses remain uncertain because broad Balmer-line virial estimates may be distorted by dense gas and poorly constrained geometry. They calculate tidal disruption event and quasi-periodic eruption rates for three LRD populations: genuinely overmassive black holes, systems on local black-hole–stellar-mass relations, and a substantially larger obscured population of lower-mass black holes. With a Hernquist distribution containing a Bahcall–Wolf cusp, the hidden low-mass population predicts markedly higher surface densities, reaching 3.37 × 10^-2 TDEs and 4.96 × 10^-1 QPE births yr^-1 deg^-2, making wide-field Euclid, Roman, and LSST light curves a potential discriminator of early black-hole demographics and LRD gas envelopes.

Key figures to inspect

• Figure 3. This figure defines the paper’s three competing black-hole–host-mass prescriptions by placing reported LRD measurements, electron-scattering-calibrated masses, envelope and quasi-star models, and local versus inferred intrinsic scaling relations on the same plane. It is essential context for understanding what the transient-rate scenarios physically represent.
• Figure 4. This figure shows how the rest-frame TDE rate depends on black-hole mass, stellar mass, and the assumed inner stellar-density slope. It provides the loss-cone physics behind why a steep Bahcall–Wolf-like cusp and a low-mass black-hole population can strongly alter the observable transient yield.
• Figure 5. This figure gives the corresponding QPE birth rates after replacing the tidal-disruption loss-cone scale with the much larger gas-photosphere scale. It makes clear why QPEs can be enhanced by orders of magnitude relative to TDEs and ties the proposed observable directly to extended dense envelopes around LRD black holes.
• Figure 6. This is the conclusion-driving population-level comparison: per-square-degree TDE and QPE rates for all three LRD scenarios are set against annual survey-area thresholds. It shows that the obscured, numerous low-mass black-hole scenario predicts systematically higher TDE rates, while density-profile and size assumptions leave the overmassive and local-scaling cases comparatively degenerate.