This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study finds that two early-universe objects thought to be faint quasars are actually extraordinarily luminous galaxies powered by bursts of star formation. James Webb Space Telescope observations of the galaxies, seen when the universe was less than a billion years old, reveal signatures of extremely massive stars, including some potentially more than 200 times the mass of the sun.
The paper outlining this discovery was posted to the arXiv preprint server on Aug. 18. There's a luminosity range where ultraviolet-bright galaxies and faint quasars become impossible to tell apart using standard discovery techniques. Both can show blue ultraviolet continua and prominent hydrogen Lyman-alpha emission lines, and low-sensitivity discovery spectra alone cannot distinguish which is which.
This ambiguity affects how astronomers count quasars and extremely bright, actively star-forming galaxies in the early universe. During their quasar searches, astronomers have detected a significant number of UV-bright galaxy candidates in the Subaru High-z Exploration of Low-Luminosity Quasars survey (SHELLQs). Among these UV-bright galaxies is a subclass called Extreme UV Luminous Galaxies (EUVLGs), which displays key features that can rule out quasars.
These include: In this study, a team led by Sarah E. Bosman of Leiden University examines two objects, J1450−0144 at redshift 6.63 and J1429−0104 at redshift 6.80, which were originally found and classified as faint quasars by SHELLQs. They were observed when the universe was under 900 million years old.
Researchers used JWST/NIRSpec spectroscopy and Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 millimeter-wave imaging to revisit both objects in detail. The JWST spectroscopy revealed features such as P Cygni wind profiles and extremely strong, broad helium (He II) emission. It also showed no broad Lyman-alpha or Mg II emission.
These findings are inconsistent with a quasar. Models incorporating stellar populations with a maximum birth mass of 100 times that of the sun could not reproduce the strong helium signal. Only models that account for very massive stars (VMS)—stars exceeding 100 times the sun's mass—could match the data.
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