Scientists have found compelling observational evidence of supermassive "first stars" in a galaxy called GS 3073 that blazed in the early universe.
The data confirms a key prediction about how the first quasars - extraordinarily bright, actively-feeding black holes - were formed.
This marks the first time scientists have found compelling evidence for such massive stars in the fossil record of the universe.
For two decades, astronomers have puzzled over how supermassive black holes - some of the brightest objects in the universe - could exist less than a billion years after the Big Bang. Normal stars simply couldn't create such massive black holes quickly enough.
Now, using the James Webb Space Telescope (JWST), an international team has found the first compelling evidence that solves this cosmic mystery: "monster stars" weighing between 1,000 and 10,000 times the mass of our Sun existed in the early universe.
The breakthrough came from examining chemical signatures in a galaxy called GS 3073. A study led by the University of Portsmouth in England and the Center for Astrophysics (CfA), Harvard and Smithsonian in the US discovered an extreme imbalance of nitrogen to oxygen that cannot be explained by any known type of star.
In 2022, researchers published work in Nature predicting that supermassive stars naturally formed in rare, turbulent streams of cold gas in the early universe, explaining how quasars (extraordinarily bright black holes) could exist less than a billion years after the Big Bang.
With GS 3073, we have the first observational evidence that these monster stars existed
Dr Daniel Whalen, Institute of Cosmology and Gravitation
"Our latest discovery helps solve a 20-year cosmic mystery," said Dr Daniel Whalen from the University of Portsmouth's Institute of Cosmology and Gravitation. "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."
The key to the discovery was measuring the ratio of nitrogen to oxygen in GS 3073. The galaxy contains a nitrogen-to-oxygen ratio of 0.46 - far higher than can be explained by any known type of star or stellar explosion.
Devesh Nandal from the CfA's Institute for Theory and Computation explained: "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."
The researchers modelled how stars between 1,000 and 10,000 solar masses would evolve and what elements they would produce. They found a specific mechanism that creates massive amounts of nitrogen:
1. These enormous stars burn helium in their cores, producing carbon.
2. The carbon leaks into a surrounding shell where hydrogen is burning.
3. The carbon combines with hydrogen to create nitrogen through the carbon/nitrogen/oxygen (CNO) cycle.
4. Convection currents distribute the nitrogen throughout the star.
5. Eventually, this nitrogen-rich material is shed into space, enriching the surrounding gas.
The process continues for millions of years during the star's helium-burning phase, creating the nitrogen excess observed in GS 3073.
The models, published in Astrophysical Journal Letters , also predict what happens when these monster stars die. They don't explode, instead, they collapse directly into massive black holes weighing thousands of solar masses.
Interestingly, GS 3073 contains an actively feeding black hole at its centre - potentially the very remnant of one of these supermassive first stars. If confirmed, this would solve two mysteries at once - where the nitrogen came from and how the black hole formed.
The study also found that this nitrogen signature only appears in a specific mass range. Stars smaller than 1,000 solar masses or larger than 10,000 solar masses don't produce the right chemical pattern for the signature, suggesting a "sweet spot" for this type of enrichment.
These findings open a new window into the universe's first few hundred million years - a period astronomers call the "cosmic Dark Ages" when the first stars ignited and began transforming the simple chemistry of the early universe into the rich variety of elements we see today.
The researchers predict that JWST will find more galaxies with similar nitrogen excesses as it continues surveying the early universe. Each new discovery would strengthen the case for these ultra-massive first stars.
