A popular model for primordial black holes is that they were seeds for galaxies and stars. Even a small black hole would attract matter into it, forming a galactic nebula, and the denser gas around the black hole would trigger the formation of early stars. This would explain why galaxies formed early in the universe, and also why most galaxies contain a supermassive black hole. Some argue that primordial black hole seeds play an essential role in the formation of early galaxies. Without black holes to trigger the process, galaxies would not have formed early. To examine this question, the team created a simulation on a massive supercomputer known as Stampede2. From their simulations, the team found that primordial black holes can encourage galaxy formation and star production, but they can also hinder it. Remove all ads on Universe Today Join our Patreon for just $3! Get the ad-free experience of a lifetime Primordial black holes could have drawn matter towards them to trigger star formation, but the matter consumed by a black hole also heats nearby gas, forcing it away. Thus, primordial black holes turn out to have a give-and-take effect. Gravitational attraction of matter to galactic clouds, but also heating of the central region and inhibition of star production. Thus, primordial black holes do not play a decisive role. The effects of seeding and heating almost cancel each other out. Smaller changes in initial conditions can determine whether a primordial black hole is a help or a hindrance to early galaxy formation. The simulations show how varying numbers of primordial black holes affect galaxy formation. Credit: Liu, et al Of course, things can change significantly with the introduction of dark matter. Dark matter is attracted to a black hole gravitationally, but does not heat nearby material like normal matter. The primordial black holes and dark matter could have cooperated in a way that neutralized any heating from the primordial black holes. If this is the case, the interaction of dark matter and primordial black holes could have created gravitational waves. These waves are too faint to detect right now, but future gravitational wave telescopes may. These detailed simulations show how subtle and complex the role of primordial black holes can be. As the team moves toward creating even more detailed simulations, they hope to see how dark matter, primordial black holes, and star production can lead to the formation of supermassive black holes. In time they could tell us how such large objects have such small beginnings. Reference: Liu, Boyuan, Saiyang Zhang, and Volker Bromm. “Stellar mass effects of primordial black holes on the formation of the first star.” Monthly Notices of the Royal Astronomical Society 514.2 (2022): 2376–2396.
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