Little red dot (astronomical object)
Little red dots are a class of small, red-tinted astronomical objects discovered by the James Webb Space Telescope. Their discovery was announced in March 2024, and they are poorly understood due to limited data collection. They appear to have existed between 0.6 and 1.6 billion years after the Big Bang, with a majority found around 600 million years post-Big Bang. As of 2025, 341 LRDs have been identified with JWST. They are extremely difficult to observe, even with JWST, being "at the limits" of that telescope's observational capability.
The current leading theory is that the LRDs are a form of primordial galaxy, and the original reports identified LRDs as a type of early active galactic nucleus containing a supermassive black hole. However, while this explains their age and appearance, they do not have the same characteristics as known AGNs. For example, they do not appear to emit X-rays, have a flattened rather than steeply rising infrared spectrum, and display very little variability between themselves. In July 2025 it was proposed that instead, LRDs were supermassive non-metallic primordial starsalso known as population III starsof perhaps a million solar masses, seen in the last few thousands of years of their lifetime.
Theoretical modelling of such stars appeared to closely match the spectrum features and luminosity of LRD, including the presence of a "strong, broad Hβ emission line alongside other Balmer lines in absorption", and in particular the photosphere of such a star would cause the V-shaped Balmer break seen in LRDs. The authors further hypothesised that such stars were progenitors of supermassive black holes, also explaining the early development of the latter objects.
Other theories are that they are quasi-stars, or similar objects consisting of a black hole surrounded by a gaseous envelope.
As active galactic nuclei
LRDs were first selected by photometric methods because they are blue in ultraviolet and red in the optical spectrum. 80% were found to have very broad Balmer emission lines, suggesting that they are active galactic nuclei and host supermassive black holes at their center. Active galactic nuclei are defined as small regions in the centers of galaxies that emit copious amounts of energy in the form of bright jets and winds. Scientists study the properties of AGNs to better understand supermassive black hole formation and how they contribute to the structure and dynamics of LRDs. One property of LRDs explained by the AGN theory is the red color of the galaxies themselves. Astrophysicists have determined that the distinct color can be accredited to the massive amounts of gas, dust, and electromagnetic energy that surrounds the AGN and supermassive black hole. This region is also known as the accretion disk.The gas in LRDs spins extremely fast. Scientists argue that the gas is accelerated to these extreme speeds by spinning, supermassive black holes. A team working under the Webb Telescope targeted LRDs in the 'Red Unknowns: Bright Infrared Extragalactic Survey', observing rapid gas orbits of roughly a strong indicator of black hole accretion.
On the other hand, LRDs also exhibit properties that are difficult to explain within the AGN scenario. For example, they have a flat infrared spectrum and lack x-ray detection. LRDs also show very weak time variability, which are often seen in AGN observation.
Observed properties
Several models have been proposed to explain the observed properties of LRDs. The shape of the ultraviolet spectrum can be explained by the scattered AGN light or by the gray dust extinction law.Research has shown that LRDs do not commonly exist at lower redshifts. One possible reason for this observation is "inside-out growth." When a galaxy evolves and expands outward from its nucleus at lower redshifts, a decreasing amount of gas is deposited near the accreting black hole. Thus, the black hole sheds its outer gas layers, becomes bluer, and is no longer categorized as an LRD.
Most are extremely compact, averaging around 2% of the radius of the Milky Way. A typical LRD has a radius no greater than 500 light-years, though many have radii smaller than 150 light-years.
Likely local analogues of LRDs were discovered in a sample of Green Pea galaxies. These are broad-line AGN-hosting Green Peas with V-shaped rest-frame UV-to-optical spectral energy distribution. Seven such V-shaped BLGPs were identified from a sample size of 2,190. These V-shaped BLGPs host over-massive black holes.
RUBIES
RUBIES, the "Red Unknowns: Bright Infrared Extragalactic Survey", is a JWST program led by Anna de Graaff and Gabriel Brammer that observed ~300 "very red sources" in the Ultra Deep Survey and Extended Groth Strip fields.Notable LRDs
; The Cliff :; CAPERS-LRD-z9: CAPERS-LRD-z9 is an LRD confirmed to be a broad-line active galactic nucleus with the red-shift z = 9.288. It is a highest red-shift AGN known. CAPERS-LRD-z9 exhibits a prominent Balmer break and "provides strong evidence in support of the 'dense-gas-enshrouded AGN'" explanation.
; A2744–45924: The LRD A2744–45924 is located in the Abell 2744 field, and is the most optically-luminous LRD found by JWST.
; RUBIES-BLAGN-1: RUBIES-BLAGN-1 is an LRD which is "an unusually bright LRD observed as part of the RUBIES program. This LRD exhibits broad emission lines, a blue UV continuum, a clear Balmer break, and a red continuum sampled out to rest-frame 4 μm with MIRI."
;J1007_AGN: The LRD J1007_AGN has a red-shift z = 7.3, and is "embedded in an overdensity of eight nearby galaxies".
;Abell2744-QSO1: Abell 2744-QSO1 is an LRD with z = 7.04. It was described as a "naked" black hole, because very few stars are in its vicinity.
;MoM-BH*-1: MoM-BH*-1 is a prominent LRB described as "a higher-redshift analogue of The Cliff".