What is the first green star discovery and why is it unusual?

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1. 1

   Galaxy Zoo Green Peas: discovery of a class of compact extremely star-forming galaxies

   Monthly Notices of the Royal Astronomical Society (Cardamone et al.)Published Sep 7, 2009Checked Oct 17, 2026

   “The star-forming Peas are low-mass galaxies (M∼ 108.5–1010 M⊙) with high star formation rates (∼10 M⊙ yr−1), low metallicities (log[O/H]+ 12 ∼ 8.7) and low reddening [E(B−V) ≤ 0.25] and they reside in low-density environments. They have some of the highest specific star formation rates (up to ∼10−8 yr−1) seen in the local Universe, yielding doubling times for their stellar mass of hundreds of Myr. The few star-forming Peas with Hubble Space Telescope imaging appear to have several clumps of bright star-forming regions and low surface density features that may indicate recent or ongoing mergers. The Peas are similar in size, mass, luminosity and metallicity to luminous blue compact galaxies. They are also similar to high-redshift ultraviolet-luminous galaxies, e.g. Lyman-break galaxies and Lyα emitters, and therefore provide a local laboratory with which to study the extreme star formation processes that occur in high-redshift galaxies. Studying starbursting galaxies as a function of redshift is essential to understanding the build up of stellar mass in the Universe.”

2. 2

   RADIO DETECTION OF GREEN PEAS: IMPLICATIONS FOR MAGNETIC FIELDS IN YOUNG GALAXIES

   The Astrophysical Journal Letters (Chakraborti et al.)Published Jan 19, 2012Checked Oct 17, 2026

   “Green Peas are a new class of young, emission line galaxies that were discovered by citizen volunteers in the Galaxy Zoo project. Their low stellar mass, low metallicity, and very high star formation rates make Green Peas the nearby ( z ∼ 0.2) analogs of the Lyman break galaxies which account for the bulk of the star formation in the early universe ( z ∼ 2–5). They thus provide accessible laboratories in the nearby universe for understanding star formation, supernova feedback, particle acceleration, and magnetic field amplification in early galaxies. We report the first direct radio detection of Green Peas with low frequency Giant Metrewave Radio Telescope observations and our stacking detection with archival Very Large Array FIRST data. We show that the radio emission implies that these extremely young galaxies already have magnetic fields (≳ 30 μG) even larger than that of the Milky Way. This is at odds with the present understanding of magnetic field growth based on amplification of seed fields by dynamo action over a galaxy's lifetime. Our observations strongly favor models with pregalactic magnetic fields at μG levels.”

3. 3

   Two Peas in a Pod: The First Confirmed Dual Active Galactic Nucleus within a Green Pea Galaxy System

   arXiv (Cornell University) (Kouroumpatzakis et al.)Published Jul 20, 2026Checked Oct 17, 2026

   “Although galaxy interactions are thought to trigger episodes of rapid SMBH growth, direct observations of simultaneous accretion onto multiple SMBHs in compact, intensely star-forming galaxies are lacking. Here we report the discovery of the first confirmed dual active galactic nucleus (AGN) in a Green Pea system, SDSS J162209.41+352107.5. Chandra imaging resolves two luminous hard X-ray sources separated by 8.4 kpc in projection, demonstrating simultaneous accretion onto two SMBHs. Follow-up Keck spectroscopy confirms that the two optical nuclei share a common redshift and independently exhibit broad Balmer emission and high-ionization AGN emission lines. Unlike most known dual AGN, which are typically found in massive mergers, J162209.41+352107.5 is a compact low-mass system analogous to galaxies thought to dominate early phases of galaxy assembly. These findings demonstrate that efficient growth of multiple SMBHs can occur in such environments and establish Green Pea galaxies as nearby laboratories for investigating the interplay between galaxy interactions, star formation, and black-hole growth under conditions analogous to those prevalent in the young Universe.”

4. 4

   Properties of the KISS Green Pea Galaxies

   The Astrophysical Journal (Brunker et al.)Published Jul 1, 2020Checked Oct 17, 2026

   “The defining characteristic of GP galaxies is a high-excitation nebular spectrum with very large equivalent width lines, leading to the recognition that GP-like galaxies can also be identified in samples of emission-line galaxies. Here we compare the properties a sample of [O iii]-selected SFGs (z = 0.29–0.41) from the KPNO International Spectroscopic Survey (KISS) with the color-selected GPs. We find that the KISS [O iii]-selected galaxies overlap with the parameter space defined by the color-selected GPs; the two samples appear to be drawn from the same population of objects. We compare the KISS GPs with the full Hα-selected KISS SFG sample (z < 0.1) and find that they are extreme systems. Many appear to be young systems at their observed look-back times (3–4 Gyr), with more than 90% of their rest-frame B-band luminosity coming from the starburst population. We compute the volume density of the KISS red (KISSR) GPs at z = 0.29–0.41 and find that they are extremely rare objects. We do not see galaxies as extreme as the KISSR GPs in the local universe, although we recognize several lower-luminosity systems at z < 0.1.”

5. 5

   Discovery of five Green pea galaxies with double-peaked narrow [O iii ] lines

   Monthly Notices of the Royal Astronomical Society (Lin et al.)Published Jul 7, 2023Checked Oct 17, 2026

   “We find that these five DPGPs have blueshifted narrow components more prominent than the redshifted components, with velocity offsets of [O iii]λ5007Å ranging from 306 to 518 $\rm km\, s^{-1}$, and full widths at half maximums of individual components ranging from 263 to 441 $\rm km\, s^{-1}$. By analysing the spectra and the spectral energy distributions (SEDs), we find that they have larger metallicities and stellar masses compared with other GPs. The H α line width, emission-line diagnostic, mid-infrared colour, radio emission, and SED fitting provide evidence of the AGN activities in these DPGPs. They have the same spectral properties of type 2 quasars. Furthermore, we discuss the possible nature of the double-peaked narrow emission-line profiles of these DPGPs and find that they are more likely to be dual active galactic nuclei (AGNs). These DPGP galaxies are ideal laboratories for exploring the growth mode of AGNs in the extremely luminous emission-line galaxies, the co-evolution between AGNs and host galaxies, and the evolution of high-redshift galaxies in the early Universe.”