The cosmic ceiling: why stars might have a maximum possible size
In short: Is there a limit to how big a star can grow? While we see massive celestial bodies, our current understanding of nuclear fusion suggests a physical wall. By surveying the night sky, astronomers have identified a specific mass threshold where the number of stars begins to drop off sharply.
To determine if supermassive stars are a reality or a theoretical impossibility, astrophysicists use two primary methods. First, they look at the physics of nuclear fusion, where stars fuse hydrogen into helium to create energy that counteracts the inward pull of gravity. Second, they perform a census of the observable universe, counting stars of various masses to see if there is a natural cutoff point.
Current observations of the stars we can see today show a distribution that drops off significantly at approximately 150 times the mass of our Sun. This suggests that for stars forming in the current epoch of the universe, there may be a physical limit to how much mass they can accumulate before the internal pressure can no longer support the structure against gravity.
However, this limit might be a product of our current era rather than a universal law. The conditions in the early universe were vastly different. Some scientists hypothesize that supermassive stars could have existed in those primitive conditions, providing a 'head start' for the formation of supermassive black holes. These monster objects, which can range from tens of thousands to billions of solar masses, were already observed in galaxies formed within the first billion years of the universe's existence.
While our own galaxy's central black hole, Sagittarius A*, is relatively modest at 4 million solar masses, others like the one in Holmberg 15A reach at least 40 billion solar masses. Whether these giants began as the collapsed remains of supermassive stars or grew through other mechanisms remains one of the most significant mysteries in modern astrophysics.
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Sources
- Summary by Intellect · source: SUPERMASSIVE stars: fact or fiction?
- Also: Types - NASA Science
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