Universe Today
One of the greatest mysteries the James Webb Space Telescope (JWST) was developed to investigate was the birth of supermassive black holes (SMBHs). For more than twenty years, astronomers have puzzled over how these gravitational behemoths - weighing millions to billions of solar masses - could exist less than a billion years after the Big Bang. According to the most widely accepted cosmological models, massive black holes did not have enough time to form through the usual processes of black hole formation and mergers.
Recent observations have challenged these models and supported the alternative hypothesis that the "seeds" of SMBHs formed directly from collapsing clouds of cosmic gas, known as the direct collapse black holes (DCBHs). The only alternative is that stars existed during the early Universe (Population III stars) that were massive enough to leave behind a massive black hole. Using the JWST, an international team has found the first evidence supporting the theory that "monster stars" of 1,000 to 10,000 solar masses existed in the early Universe.
The team was led by Devesh Nandal, a Swiss National Science Foundation Postdoctoral Fellow from the University of Virginia and the Institute for Theory and Computation (ITC) at the Harvard & Smithsonian Center for Astrophysics (CfA). He was joined by Daniel Whalen, a Senior Lecturer in Cosmology at the Institute of Cosmology and Gravitation (ICG) at the University of Portsmouth; Muhammad A. Latif, an astrophysicist from United Arab Emirates University (UAEU), and Alexander Heger, a researcher from the School of Physics and Astronomy at Monash University.
*Artist’s impression of a field of Population III stars as they would have appeared just 100 million years after the Big Bang. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Zamani*
Using the JWST, the team examined chemical signatures in GS 3073, a galaxy originally identified in 2022 by Latif, Whalen, and colleagues from the Institute for Astronomy (IfA) at the University of Edinburgh, the University of Exeter, and the Herzberg Astronomy and Astrophysics Research Centre. At the time, the discovery team noted an extreme nitrogen-to-oxygen ratio (0.46), far higher than could be explained by any known type of star or stellar explosion. This led them to theorize that the first stars in the Universe, known as Population III, formed from turbulent flows of cold gas a few hundred million years after the Big Bang.
They also noted that GS 3073 contains an actively feeding black hole at its center, which could be the remnant of one of these "monster stars." The existence of this kind of stellar object, they claimed, would explain why Webb had detected multiple quasars that existed less than 1 billion years after the Big Bang. Also known as Active Galactic Nuclei (AGNs), this phenomenon is caused by SMBHs at the centers of galaxies, which accelerate infalling gas and dust to close to the speed of light. This causes tremendous amounts of energy to be released in the process, causing the core region to temporarily outshine all of the stars in the disk. Said Nandal in a University of Portsmouth press release::
Chemical abundances act like a cosmic fingerprint, and the pattern in GS3073 is unlike anything ordinary stars can produce. Its extreme nitrogen matches only one kind of source we know of - primordial stars thousands of times more massive than our Sun. This tells us the first generation of stars included truly supermassive objects that helped shape the early galaxies and may have seeded today’s supermassive black holes.
To test this theory, Latif, Whalen, and their team modeled how stars of 1,000 to 10,000 solar masses would evolve and what chemicals they would produce. This allowed them to identify a specific mechanism that would account for the nitrogen-to-oxygen ratio observed in GS3073. It begins with monster stars fusing helium in their cores to produce carbon, which leaks into the surrounding shell where hydrogen is being fused. Once there, the carbon combines with hydrogen to form nitrogen, which is distributed throughout the star by convection currents and is eventually released into space.
*Graphic detailing how "monster stars" create the type of nitrogen excess observed around GS3073. Credit: Institute of Cosmology and Gravitation/University of Portsmouth*
This process will continue as long as helium is fused in the core (for millions of years), enriching the gas cloud surrounding environment until the nitrogen-to-oxygen ratio is observed. The team's model also suggests that these monster stars do not explode as supernovae at the end of their life cycle, but collapse directly into massive black holes that are the "seeds" of SMBHs observed today. They also found that this nitrogen signature did not occur in stars that are smaller or larger than those in this mass range. If confirmed, these stars would explain two mysteries emerging from Webb's previous observations.
What's more, these findings are providing fresh insight into the Universe as it existed between 380,000 and 1 billion years after the Big Bang - aka the "Cosmic Dark Ages." Until recently, this cosmological epoch was inaccessible to astronomers because light from this period is too faint for conventional instruments to observe today, requiring cutting-edge infrared optics like those used by the JWST. The researchers predict that more galaxies with similar nitrogen excesses will turn up in future surveys, allowing scientists to investigate the potential existence of "monster stars" further. Said Whalen:
Our latest discovery helps solve a 20-year cosmic mystery. With GS 3073, we have the first observational evidence that these monster stars existed. These cosmic giants would have burned brilliantly for a brief time before collapsing into massive black holes, leaving behind the chemical signatures we can detect billions of years later. A bit like dinosaurs on Earth - they were enormous and primitive. And they had short lives, living for just a quarter of a million years - a cosmic blink of an eye.
Further Reading: University of Portsmouth, Nature
