Astrophysics

No evolution in the number density of little red dots from cosmic dawn to cosmic noon

Federica Loiacono, Roberto Gilli

Featured July 10, 2026

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Simply

Tiny, red, X-ray-quiet objects in the early universe, called little red dots, are found to be just as common at "cosmic noon" as they were earlier, suggesting they play a big role in growing black holes.

In depth

The paper reveals that little red dots (LRDs), a unique class of X-ray silent active galactic nuclei, maintain a consistent abundance from the early universe (cosmic dawn) to a later epoch (cosmic noon). This finding, based on a rigorous selection and bolometric luminosity function analysis, challenges prior models suggesting a sharp decline in their numbers, implying a sustained role in early black hole growth.

Key Takeaways

1
The study identifies five X-ray silent, broad-line emitters in the J1030 field, classifying them as LRDs or LBDs, and derives their bolometric luminosities and black hole masses.
2
The paper's primary breakthrough is demonstrating no significant evolution in the number density of LRDs ( $L_{b o l} ≳ 3 \times 1 0^{44}$ erg s $^{- 1}$ ) from cosmic dawn ( $z \sim 7$ ) to cosmic noon ( $z \sim 2.4$ ).
3
The observed abundance of LRDs at cosmic noon is significantly higher than some model predictions, suggesting either efficient black hole seed formation at later epochs or that LRDs represent a high-accretion phase of already mature black holes.

Conceptual Flow

HIGH LEVEL

Methodology: How was it done?

Scientists used a powerful space telescope to find special red dots in the sky, then measured their light and how many there were at different times.

Sky Images

Light Spectra

Find Red Dots, Measure Brightness

Count of Red Dots

Brightness Chart

Results: What did they find?

They discovered that these red dots were just as common in the early universe as they were later, which was a surprise because many thought they would disappear.

Early Universe Count

Later Universe Count

Compare Numbers

No Change Found