Blueberry galaxy

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.