The X-Ray Dot: Exotic Dust or a Late-stage Little Red Dot?

Hviding, RE; de Graaff, A; Liu, H; Goulding, AD; Ma, Y; Greene, JE; Boogaard, LA; Bunker, AJ; Cleri, NJ; Franx, M; Hirschmann, M; Leja, J; Matthee, J; Naidu, RP; Setton, DJ; Übler, H; Venturi, G; Wang, B

Journal article

The X-Ray Dot: Exotic Dust or a Late-stage Little Red Dot?

Abstract:: JWST’s “little red dots” (LRDs) are increasingly interpreted as active galactic nuclei (AGN) obscured by dense thermalized gas rather than dust as evidenced by their X-ray weakness, blackbody-like continua, and Balmer line profiles. Key questions are how LRDs connect to standard UV-luminous AGN, whether transitional phases exist, and whether they are observable. We present the “X-ray dot” (XRD), a compact source at z = 3.28 observed by the NIRSpec Wide Guaranteed Time Observation survey. The XRD exhibits LRD hallmarks: a blackbody-like (Teff ≃ 6400 K) red continuum, a faint but blue rest-UV excess, falling mid-IR emission, and broad Balmer lines (FWHM ∼ 2700–3200 km s−1). Unlike LRDs, however, it is remarkably X-ray luminous (L2−10 keV = 1044.18 erg s−1) and has a continuum inflection that is blueward of the Balmer limit. We find that the red rest-optical and blue mid-IR continuum cannot be reproduced by standard dust-attenuated AGN models without invoking extremely steep extinction curves, nor can the weak mid-IR emission be reconciled with well-established X-ray–torus scaling relations. We therefore consider an alternative scenario: the XRD may be an LRD in transition, where the gas envelope dominates the optical continuum but optically thin sight lines allow X-rays to escape. The XRD may thus provide a physical link between LRDs and standard AGN, offering direct evidence that LRDs are powered by supermassive black holes and providing insight into their accretion properties.

Publication status:: Published

Peer review status:: Peer reviewed

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APA Style

Hviding, R. E., de Graaff, A., Liu, H., Goulding, A. D., Ma, Y., Greene, J. E., Boogaard, L. A., Bunker, A. J., Cleri, N. J., Franx, M., Hirschmann, M., Leja, J., Matthee, J., Naidu, R. P., Setton, D. J., Übler, H., Venturi, G., & Wang, B. (2026). The X-Ray Dot: Exotic Dust or a Late-stage Little Red Dot? The Astrophysical Journal Letters, 1000(1), L18.

MLA Style

Hviding, RE, et al. “The X-Ray Dot: Exotic Dust or a Late-Stage Little Red Dot?” The Astrophysical Journal Letters, vol. 1000, no. 1, 2026, p. L18.

Chicago Style

Hviding, RE, A de Graaff, H Liu, et al. 2026. “The X-Ray Dot: Exotic Dust or a Late-Stage Little Red Dot?” The Astrophysical Journal Letters 1000 (1): L18.
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