Radio Reveals Star Birth in the Early Universe express
A radio telescope has caught signals from three galaxies that existed when the universe was less than a billion years old. Their radio glow is so powerful that each seems to be birthing a thousand suns per year in a short span. For comparison, our Milky Way produces only a couple of stars per year.
Initially, these galaxies were spotted in images from the Hubble and James Webb space telescopes: they looked unusually red due to their immense distance. Then spectroscopy confirmed that their light has been traveling for 12.8–13.1 billion years. Next, radio telescopes took over and showed that all the emission is created by stars, not by a black hole at the center.
Two of the three galaxies have a ragged, multi-component shape. They appear to have just undergone a collision with a neighbor, and that collision compressed gas, triggering an avalanche of star formation. This is how the first large clusters of stars ignited in the early universe.
Original abstract
as written by the authors arXiv:2602.05808
Radio observations offer a dust-independent probe of star formation and active galactic nucleus (AGN) activity, but sufficiently deep data are required to access the crossover luminosity between these processes at high redshift ($$z>4.5$$). We present three spectroscopically confirmed high-redshift radio sources (HzRSs) detected at 1.3 GHz at $$z=4.9$$-$$5.6$$, with radio luminosities spanning $$L_{\rm 1.3 \, GHz}\approx2$$-$$5\times10^{24} \, \rm W \, Hz^{-1}$$. These sources were first identified as high-redshift candidates through spectral energy distribution (SED) fitting of archival Hubble, JWST NIRCam+MIRI, and ground-based photometry, and then spectroscopically confirmed via the $$\rm H\,\alpha$$ emission line using wide-field slitless spectroscopy from JWST COSMOS-3D. The star formation rates (SFRs) measured from SED fitting, the $$\rm H\,\alpha$$ flux, and the 1.3 GHz luminosity, span $$\sim100$$-$$1800\, M_{\odot} \, \rm yr^{-1}$$, demonstrating broad agreement between these SFR tracers. We find that these three sources lie either on or $$0.5$$-1.0 dex above the star-forming main sequence at $$z=4$$-6 and have undergone a recent burst of star formation. The sources have extended rest-UV/optical morphologies with no evidence for a dominant point source component, indicating that an AGN is unlikely to dominate their rest-UV and optical emission. Two of the sources have complex, multi-component rest-frame UV/optical morphologies, suggesting that their starbursts may be triggered by merging activity. These HzRSs open up a new window towards probing radio emission powered by star formation alone at $$z> 4.5$$, representing a remarkable opportunity to begin tracing star formation, independent of dust, in the early Universe.
Light from these galaxies has been traveling for nearly 13 billion years — three times the age of Earth.