Little red dot variability over a century reveals black hole envelope via a giant Einstein cross

2025/12/04 by Zhang, Zijian, Li, Mingyu, Oguri, Masamune +79 · 1 citation
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences

paper · doi:10.48550/arxiv.2512.05180

Abstract

"Little red dots" (LRDs) represent a new population of astronomical objects uncovered by JWST whose nature remains debated. Although many LRDs are suspected as active galactic nuclei (AGN), they show little variability on days-years timescales. We report the discovery of two gravitationally lensed LRDs at redshift ∼4.3 behind the cluster RXCJ2211-0350, one of which (RX1) is quadruply imaged with time delays spanning ∼130 years. RX1 exhibits intrinsic color and brightness variations of up to 0.7 magnitude among its images. These changes are consistent with blackbody-temperature variations of a photosphere, indicating long-term variability analogous to Cepheid-like pulsations but in a far more extended (R ∼ 2000 AU) and massive (M \gtrsim 10⁶ M_\odot) systems. These results suggest LRDs as a distinct class of AGN with stellar-like envelopes.

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