X-ray View of Little Red Dots: Do They Host Supermassive Black Holes?

The discovery of Little Red Dots (LRDs) – a population of compact, high-redshift, dust-reddened galaxies – is one of the most surprising results from JWST. However, the nature of LRDs is still debated: some studies suggest that these galaxies host accreting supermassive black holes (SMBHs), while others conclude that the near-infrared emission primarily originates from intense star formation. In this work, we utilize ultra-deep Chandra observations and study LRDs residing behind the lensing galaxy cluster, Abell 2744. We probe the X-ray emission from individual galaxies but find that they remain undetected and provide SMBH mass upper limits of ≲(1.5-16)×10^6 M_⊙ assuming Eddington limited accretion. To increase the signal-to-noise ratios, we conduct a stacking analysis of the full sample with a total lensed exposure time of ≈87 Ms. We also bin the galaxies based on their stellar mass, lensing magnification, and detected broad-line Hα emission. All but one stacked sample remains undetected with SMBH mass upper limits of ≲2.5×10^6 M_⊙. We obtain a tentative, ≈2.6σ detection for LRDs exhibiting broad-line Hα emission. Taking this detection at face value, the inferred mean SMBH mass is ≈3.2×10^6 M_⊙ assuming Eddington-limited accretion, about 1.5 orders of magnitude lower than that inferred from JWST data. Our results imply that LRDs do not host over-massive SMBHs and/or accrete at a few percent of their Eddington limit. The significant discrepancy between the JWST and Chandra data hints that the scaling relations used to infer the SMBH mass from the Hα line and virial relations may not be applicable for high-redshift LRDs.