According to the Big Bang theory, the Universe began around 13.8 billion years ago as a hot, dense state that expanded rapidly, exhibiting only minor density variations. Surprisingly, even when we examine the Universe's first billion years, we discover hundreds of black holes with masses reaching hundreds of millions or even billions of times that of our Sun. This has been a longstanding enigma: how did these black holes form so early and grow so massive so quickly? After extensive research, we've finally deciphered this cosmic mystery.
Imagine being able to observe every person on Earth as they were at five years old. You would see a variety of traits—differences in height, weight, foot size—but you'd expect them all to look like five-year-olds. Discovering one that resembled a teenager or adult would rightfully make you question whether your observations reflected reality.
In the Universe, however, this is exactly what we observe with the earliest, brightest galaxies that harbor black holes. Theoretically, there should be constraints on:
- When the first stars, and therefore the first black holes, can form,
- The maximum size of an initial black hole formed from these stars,
- And the speed at which these black holes can gain mass.
Yet, in the Universe's first few hundred million years, we find supermassive black holes that vastly exceed these anticipated constraints. After 19 years of research, a team has presented a solution in a new paper published in Nature. Here’s how the Universe likely achieves this:
Initially, during the hot Big Bang, the Universe was nearly perfectly uniform. If you imagined a sphere encompassing any space region, you would find a specific mass within it. Repeating this with 1,000 differently positioned but identically sized spheres would show:
- About 683 spheres held between 99.997% and 100.003% of the average density,
- Approximately 954 spheres held between 99.994% and 100.006% of the average density,
- Roughly 997 spheres held between 99.991% and 100.009% of the average density,
- All 1,000 spheres contained between 99.988% and 100.012% of the average density.
This suggests that, even at the Big Bang's inception, the densest areas were only marginally more massive than average.
Given this near-uniformity and the physics governing matter and radiation in the early Universe, we can predict the timeframe needed for even the densest regions to gather enough mass to create the first stars and black holes. Although some uncertainties remain, it's universally accepted that tens of millions of years are necessary for the first stars to form, with the initial significant wave of star formation occurring between 100 and 200 million years after the Big Bang.
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