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

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.

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:

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:

In "FAST H I 21 cm Study of Blueberry Galaxies" (Chandola et al 2024) 28 BBs are studied using the Five-hundred-meter Aperture Spherical Telescope. The sample of BBs are observed over a 3 year period using FAST to measure the H I, or neutral hydrogen, using the 21 cm spectral line. By finding out the H I levels, the depletion rate of any H I 'reservoirs' can be deduced. Generally, the lower the stellar mass, the higher the amount of H I is present i.e. has not yet been used up in star formation. Two of the 28 are found to have these reservoirs and overall, only 7% of the 28 have an H I detection, which are lower values than those of main sequence galaxies.

The study "Blueberry galaxies up to 200 Mpc and their optical and infrared properties" (Kouroumpatzakis et al. 2024) analyses 48 BBs. Using data from the HECATE catalog, photometry from Pan-STARRS, SDSS and ALLWISE, and spectroscopy from MPA-JHU, 40 previously known BBs and 8 unknowns were identified. 14 of the 48 were from the less-studied southern hemisphere. They conclude that BBs are the most intensely starforming sources among dwarf galaxies in the local universe. They are less massive, more blue in visible light and redder in the infrared. BBs "have higher specific starformation rates, equivalent widths, lower metallicities, and the most strongly ionized interstellar medium compared to typical SFGs and GPs."