What are the compact red sources (little red dots) found by JWST? · revision history
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- Title
- What are the compact red sources (little red dots) found by JWST?
- Plain
- JWST found many tiny, very red objects in the young universe that show signs of a growing black hole but emit almost no X-rays and little hot dust. Whether they are black holes wrapped in dense gas, giant stars, or something else is unknown.
- Precise
- Little red dots are compact (effective radius $<\sim 100\,\mathrm{pc}$) sources, mostly at $z\sim 4-9$, with V-shaped spectral energy distributions (blue rest-UV, red rest-optical), broad Balmer emission lines ($\mathrm{FWHM}\sim 1-4x10^{8}\,\mathrm{cm}/\mathrm{s}$), strong Balmer breaks and Balmer absorption, weak X-ray and weak hot-dust emission, and number densities of order 100 times those extrapolated from UV-selected quasars. Identify the source of the continuum and of the line widths: an accreting black hole inside a dense, nearly dust-free gas envelope (black hole star), a supermassive star or quasi-star, a compact starburst, or a combination, with a model that reproduces the full spectrum.
- Settled by
- A single physical model that fits the rest-UV to mid-infrared spectra, the Balmer break and absorption, the X-ray weakness and the variability limits of a large spectroscopic sample.
- Kind
- phenomenon
- Answer type
- mechanism
- References
- (empty)
- Literature status
- contested
- Status note
- 2025-2026 spectroscopic studies favor accreting black holes inside dense gas envelopes, while supermassive-star and super-Eddington outflow models are still being proposed in 2026.
- Posed since
- 2023