# An extraordinarily massive galaxy that formed its stars at $z \gtrsim 11$

**Authors:** Karl Glazebrook, Themiya Nanayakkara, Corentin Schreiber, Claudia Lagos, Lalitwadee Kawinwanichakij, Colin Jacobs, Harry Chittenden, Gabriel Brammer, Glenn G. Kacprzak, Ivo Labbe, Danilo Marchesini, Z. Cemile Marsan, Pascal A. Oesch, Casey Papovich, Rhea-Silvia Remus, Kim-Vy H. Tran, James Esdaile, Angel Chandro Gomez  
**arXiv:** [2308.05606](https://arxiv.org/abs/2308.05606)  
**Date:** 2023-08-10  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.05606v1/

## Key points

- Formation of galaxies through hierarchical co-assembly of baryons and dark matter halos is a fundamental concept in astrophysics
- Observing massive galaxies at early times can test this paradigm
- Recent observations have revealed extremely massive quiescent galaxies as early as 1-2 billion years after the Big Bang, creating tension with theoretical models
- Researchers report on spectroscopic observations of one such massive galaxy using the James Webb Space Telescope
- This galaxy stands out due to its much redder colors
- Spectroscopic analysis reveals spectral features indicating that stars formed at least 1.5 billion years earlier at a high redshift (z)
- Finding poses a challenge to understanding early stellar populations, galaxy formation processes, and potentially even the nature of dark matter
- Current knowledge suggests dark matter halos capable of hosting these ancient stars should not have assembled at such an early cosmic epoch
- Detailed modeling and analysis suggest a significant gap in understanding early galaxy formation or properties of dark matter may explain this observation
- Further research needed to investigate this finding and refine understanding of these fundamental aspects of astrophysics

## Summary

The formation of galaxies through the gradual hierarchical co-assembly of baryons and cold dark matter halos is a fundamental concept in astrophysics. One way to test this paradigm is by observing massive galaxies at early times, as the evolution of dark matter halos can be simulated and should contain the universal cosmic baryon fraction at high redshift. However, recent observations have revealed extremely massive quiescent galaxies, with masses greater than $10^{11}$ M$_\odot$, as early as 1-2 billion years after the Big Bang. This discovery has created tension with theoretical models and necessitated significant revisions. In a new study, researchers report on spectroscopic observations of one such massive galaxy using the James Webb Space Telescope. This particular galaxy stands out from others due to its much redder colors. The spectroscopic analysis reveals spectral features typical of much older stellar populations, indicating that these stars formed at least 1.5 billion years earlier at a redshift ($z$) greater than 11 in a rapid star formation event. This finding poses a challenge to our understanding of early stellar populations, galaxy formation processes, and potentially even the nature of dark matter. According to current knowledge, dark matter halos capable of hosting these ancient stellar ancestors should not have assembled at such an early cosmic epoch. The detailed modeling and analysis conducted in this study suggest that there may be a significant gap in our understanding of early galaxy formation or the properties of dark matter which could explain this observation. Further research will be needed to investigate this intriguing finding and refine our understanding of these fundamental aspects of astrophysics. Overall, this study highlights the complexities involved in unraveling the mysteries surrounding galaxy formation and provides valuable insights into the early universe's evolution.