Asked by Marjorie Allworth
In the present-day Universe, black holes are formed from the collapsing cores of massive stars during supernova explosions. With a mass of perhaps five Suns or more, the core of such a giant star has such powerful gravity that, when the nuclear reactions that have previously supported it falter and die, it collapses under its own weight with enough force to shred its atoms into subatomic particles. The end result is a tiny point with enormous mass (a singularity), whose gravity is so powerful that nothing, not even light, can escape.
One theory is that all black holes originate in this way, and so the first black holes could not have formed until after the first generation of giant stars (perhaps 300 million years after the Big Bang). According to this model, the first black holes acted as nuclei for the creation of galaxies, drawing in raw star-forming material from the Universe around them and growing in size to become the ‘supermassive’ black holes, with the mass of millions of Suns, that lie at the core of many of today’s galaxies. In 2011, NASA’s Chandra X-ray Observatory confirmed the presence of growing black holes in the heart of many distant, ancient galaxies, which bolsters this theory.
But another theory is that the first black holes were born in the Big Bang itself, some 13.7 billion years ago. Supporters of this idea suggest that in the first moments of creation, pressures and temperatures were so great that slight fluctuations in the density of matter could create black holes spontaneously, which could then have acted as the seeds for later star and galaxy formation. The big issue with this model is that it should create black holes across a wide range of sizes, from the microscopic to the supermassive. Very small black holes are understandably hard to detect, but the predicted ‘intermediate-mass’ black holes, midway between the stellar and supermassive types, should be easy to find, and are so far conspicuous by their rarity.
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