---
title: "Blueberry galaxy"
chunk: 1/3
source: "https://en.wikipedia.org/wiki/Blueberry_galaxy"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:13:38.048281+00:00"
instance: "kb-cron"
---

Blueberry galaxies (BBs) are  dwarf   starburst galaxies that have very high ionization rates and some of the lowest stellar masses and  metallicities. 
They are smaller counterparts of  Green Pea galaxies (GPs), but

are more compact being less than 1⁄3000th the size of the Milky Way,
are less distant, existing in low-density environments that are within the local universe, and
have lower luminosities. BBs form one of the youngest classes of star-forming galaxies with median ages ~70 Myr. Two BBs are among the most metal-poor galaxies known within the local universe.
BBs were first named in the scientific literature by Yang et al. (2017) as GPs that were at a distance of redshift  z=0.05 or less, although similar galaxies had originally been named BBs on the Galaxy Zoo website. While Yang et al. identified a sample of 40 BBs, a much larger sample was acquired using data from the LAMOST DR9 survey. Liu et al. found 270 BBs, as well as GPs and "Purple Grapes". Researchers undertook a systematic study of the star formation rates, metallicities and environments of the compact galaxies that have different colours because of the different positions of  emission lines in the  photometric bands. 
BBs at redshift z < 0.05  have the [O III] λ5007 emission line within the g band, which makes their colors blue; purple grapes are those at z > 0.36 with [O III]λ5007 within the i band and the UV continuum redshifted to the g band (typically redshift 0.05 ≤ z < 0.112); GPs are in the redshift range of 0.112 < z < 0.36 and have the [O III]λ5007 line within the r band. 

== Comparison to high-redshift galaxies ==
BBs, or "peas of various colours", have recently been studied as analogs for high-redshift galaxies that have been observed by the James Webb Space Telescope (JWST) (e.g.). Three examples of this are:

"JADES: Probing interstellar medium conditions at z ~ 5.5–9.5 with ultra-deep  JWST/NIRSpec  spectroscopy" (diagram top right) examines 27 galaxies at high redshifts that were observed with JWST/NIRSpec. The study measured various emission lines from the  ultra-deep JADES survey so as to gauge the ratios between the chemicals identified and categorise them into groupings, or 'spaces'. BBs are identified as local analogs to these JADES galaxies, along with GPs, as they have "extreme properties" such as metallicity, low mass and very high ionization. They find that "galaxies in this sample occupy regions of line-ratio space that are offset from those inhabited by typical galaxies at z ~ 0 or z ~ 2, although generally aligned with more extreme low-redshift populations such as 'blueberry' and 'green pea' dwarf starbursts".
In the study "Evolution of the Mass–Metallicity Relation from Redshift z ≈ 8 to the Local Universe" (Langeroodi et al. 2023), BBs and GPs are compared to a sample of 11 galaxies from JWST that are at redshift z ≈ 8. Using NIRCam and NIRSpec spectroscopy, metallicities and stellar masses are measured and then compared to extremely low metallicity analogs such as BBs. The study finds that the z ≈ 8 sample are generally distinct from extreme emission line galaxies or GPs but are similar in strong emission line ratios and metallicities to BBs. The study finds that BBs and GPs have metallicities similar to the z ≈ 8 galaxies, but "Despite this similarity, at a fixed stellar mass, the z ≈ 8 galaxies have systematically lower metallicities compared to BBs."

The study "NGDEEP: The Star Formation and Ionization Properties of Galaxies at 1.7 < z < 3.4" (diagram bottom right) uses the JWST FGS-NIRISS from the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) Survey to investigate a sample of 178 star-forming galaxies at redshifts 1.7 < z < 3.4. Using slitless spectroscopy, the authors select galaxies with ionizing oxygen and hydrogen emission features. BBs and GPs are used extensively as comparison galaxies at redshft z ~ 0 as they have strong emission lines "which may have properties more similar to those of high-redshift galaxies". As well as 36 BBs and 43 GPs, galaxies from SDSS and 45 from the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) with similar redshifts are used all of which have ionized oxygen measurements. Among their results, they find that:
Galaxies with a redshift z ~ 2–3  have comparable or lower ionized oxygen  ratios (O32) "to that measured for extreme galaxies at z ~ 0 at the fixed stellar mass, SFR, sSFR, and Hα and Hβ EW, indicating these extreme galaxies at z ~ 0 have similar to higher ionization parameters and similar to lower metallicity" and
The authors' NGDEEP sample spans a wide range of O32 and stellar masses, "which helps bridge the gap between the local and the z > 5 universe. We find an evolutionary trend in O32 and EW(Hβ) from z ~ 0 to z ~ 5, where higher redshift galaxies show increased O32 and EW, with possibly higher O32 at fixed EW."

== Further studies ==
In "X-ray observations of Blueberry galaxies" (Adamcová et al 2024) BBs are studied using the XMM-Newton space telescope. These observations are the first to use  x-rays and deliver surprising results. Of the 7 BBs studied, only 2 were detected as having significant x-ray emissions, while the remaining 5 are considered under-luminous. One theory as to why this might be is that because the stellar population of BBs is very young and "hasn't yet evolved enough to produce binary systems with a normal star paired with a neutron star or black hole, which shine brightly in X-ray."

A massive BB named  SHOC 579 has been studied using the SDSS MaNGA survey by Paswan et al. (2022). Using data from MaNGA and a variety of sources such as GALEX and  Spitzer, a BB next to an older disk-like structure is investigated. Both objects are at redshift z=~ 0.0472. Their conclusions (shortened & quoted) find that the BB is: