---
title: "Astronomers Mistook a Brown Dwarf for the Universe's Oldest Galaxy: How JWST Revealed the Error"
description: "An MNRAS study revealed that the object Capotauro, previously mistaken for the Universe's oldest galaxy, is actually a cold Y-type brown dwarf 2,400 light-years away. The error was identified using JWST images from 2022–2026."
date: 2026-11-06T06:12:52.480Z
lang: en
url: https://xab.info/en/posts/astronomers-mistake-brown-dwarf-oldest-galaxy
tags: [astronomy, jwst, brown-dwarf, galaxy, milky-way, cosmology, capotauro]
author: "Alexander Buran"
publisher: "XAB.info"
---

# Astronomers Mistook a Brown Dwarf for the Universe's Oldest Galaxy: How JWST Revealed the Error

![Deep space field with bright galaxies and a framed brown dwarf object](https://xab.info/media/2026/11/06/astronomers-mistook-brown-dwarf-for-oldest-galaxy-jwst/astronomers-mistook-brown-dwarf-for-oldest-galaxy-jwst-1.webp)

## Key Points

- Capotauro, previously classified as the oldest galaxy in the Universe, turned out to be a cold Y-type brown dwarf in the Milky Way
- A shift of 0.13 arcseconds between JWST images (December 2022 — June 2026) proved its galactic location
- Capotauro is located about 2,400 light-years away with a surface temperature of about 350 K (77 °C)
- Scientists urge including cold brown dwarf templates when searching for ultra-distant objects in the early Universe

For several years, astronomers believed that an object named Capotauro was the oldest galaxy in the Universe, with light having traveled more than 13 billion years to reach Earth. However, a new study published in the prestigious Monthly Notices of the Royal Astronomical Society has completely revised this conclusion: Capotauro has turned out to be a cold brown dwarf located within the Milky Way, at a distance of about 2,400 light-years from Earth. The error occurred due to the similarity of absorption spectra characteristic of both very distant galaxies and cold substellar objects.

### How spectral “disguise” misled scientists

The initial classification of Capotauro as an ultra-distant galaxy was based on the features of its light spectrum. In certain ranges, the object's radiation was absorbed, and this absorption pattern resembled the hydrogen signature of very ancient galaxies located at the edge of the observable Universe. It was this resemblance that led researchers to conclude it was at a record-breaking distance. However, as subsequent observations showed, cold brown dwarfs are capable of “pretending” to be distant galaxies precisely due to similar broad absorption bands in the spectrum, making them extremely deceptive false candidates when searching for early Universe objects.

### The decisive role of JWST observations: a 0.13 arcsecond shift

Key evidence that debunked the hypothesis of Capotauro's galactic nature was a comparison of images obtained by the James Webb Space Telescope (JWST) in December 2022 and June 2026. Over the 3.5-year interval, the object shifted by 0.13 arcseconds relative to background stars. Such proper motion unequivocally indicates that Capotauro is located inside our Galaxy. If it were truly the oldest galaxy at the edge of the observable Universe, its angular movement over such a short period would be imperceptible to any existing telescope.

### What Capotauro actually is

According to new calculations, Capotauro is a Y-type brown dwarf, one of the coldest classes of substellar objects. Its surface temperature is around 350 Kelvin, equivalent to approximately 77 degrees Celsius. Located at a distance of about 2,400 light-years from Earth, it is among the most distant objects of this class ever discovered by astronomers. This makes it a valuable subject for studying the distribution and physical properties of the coldest substellar bodies in the Milky Way.

### Methodological conclusions for cosmology

Although Capotauro did not rewrite the history of the formation of the first galaxies, the discovery itself is significant for cosmological methodology. The study's authors urge the mandatory inclusion of cold brown dwarf templates in identification algorithms when searching for ultra-distant early Universe objects. Without such accounting, there is a real risk of repeating such errors, where galactic substellar objects are mistakenly classified as galaxies at extreme distances. The work demonstrates that even when using a powerful instrument like JWST, cross-validation of data from different observation eras remains an indispensable verification tool.

### The significance of the discovery for astrophysics

Despite the fact that the sensational status of the “oldest galaxy” has been removed, Capotauro provides astronomers with important data on the distribution and properties of the coldest substellar objects in the Milky Way. The detection of a Y-type brown dwarf at a distance of 2,400 light-years expands the known sample of such bodies and allows for the refinement of models of their formation and evolution. Furthermore, the case of Capotauro serves as a clear example of how the development of observational capabilities—in this case, repeat JWST shots with an interval of several years—allows for the rapid and reliable resolution of disputed classifications that would have previously remained irrefutable.

## Fact-Check & Sources

- [Астрономы перепутали карлика с древнейшей галактикой: как выявили ошибку](https://www.rbc.ua/ukr/news/astronomi-splutali-karlika-naydavnishoyu-1793892999.html) - The source contains all key facts: publication in MNRAS, JWST data (Dec 2022 / June 2026), 0.13 arcsec shift, type Y, 2,400 light-years, 350 K. No discrepancies with the foundation.

## FAQ

### Why was Capotauro initially mistaken for an ancient galaxy?

The object's absorption spectrum in certain ranges resembled the hydrogen signature of very ancient galaxies. Cold brown dwarfs can replicate these patterns, leading to an incorrect classification.

### How was it proven that Capotauro is inside the Milky Way?

Comparing JWST images taken in December 2022 and June 2026 showed a shift of 0.13 arcseconds over 3.5 years. Such proper motion is impossible for an object at the edge of the observable Universe.

### What are the main characteristics of Capotauro as a brown dwarf?

Capotauro is a Y-type brown dwarf with a surface temperature of about 350 Kelvin (77 °C), located approximately 2,400 light-years from Earth. It is one of the most distant objects of its class.

### What methodological conclusions did the scientists reach?

The authors urge that templates of cold brown dwarfs must be considered when searching for ultra-distant early Universe objects to avoid such classification errors in the future.