Almost every galaxy in the universe contains a supermassive black hole. Even galaxies that are billions of light years away. This means that supermassive black holes form early in the evolution of a galaxy. They could even be gravitational seeds that a galaxy forms around. But astronomers still don’t know exactly how these massive gravitational beasts first appeared. There are two big ideas. The first, known as the light-particle model, are massive stars in the dense center of a new galaxy that live out their short lives and die to become black holes, after which That stellar-mass black hole gradually coalesces, turning into a super black. loss over time. The second is known as the heavy seed model, in which the dense gas and dust in a nascent protogalaxy collapses directly into a black hole with an initial mass of 100,000 suns or more, followed by mature galaxy around it. The second model would explain why we see so many massive black holes in young galaxies, but it also violates the so-called Eddington limit. As matter collapses to form a star or black hole, it also heats up, and the resulting light and pressure repel gravity. Gravity will win in the end, but it takes time. The first model does not violate Eddington’s limit, but it does explain how the first black holes grew in mass so quickly. Without much observational data, astronomers can only rely on variations of these theoretical models, which are inconclusive.

Direct collapse versus gradual growth of black holes Credit: Natarajan, et al In a new study, a team of astronomers has discovered the first black hole so massive that it supports heavy particle model. It’s a quasar named UHZ1. Quasars are powered by active supermassive black holes, and from their luminosity you can tell their mass. Based on the luminosity of UHZ1, it has a mass of about 40 million suns and possibly up to 70 million suns. The quasar has a redshift of z~10.3, which means we see it at a time when the universe was just 400 million years old. It was at the end of the Dark Ages of the Universe, when the first stars were just beginning to form. Somehow, UHZ1 has become super large in an extremely short amount of time. The gradual merging of stellar-mass black holes is unlikely to produce such a massive black hole on this time scale, or at least is unlikely. The authors are careful to note that with just one example of an early supermassive black hole, we shouldn’t jump to conclusions. But this is the best evidence for the heavy particle model. References: Natarajan, P., et al. “First discovery of a supermassive black hole galaxy: UHZ1 – Evidence of a massive black hole seed from a direct collapse?” preprint arXiv arXiv:2308.02654 (2023).Direct collapse versus gradual growth of black holes Credit: Natarajan, et al In a new study, a team of astronomers has discovered the first black hole so massive that it supports heavy particle model. It’s a quasar named UHZ1. Quasars are powered by active supermassive black holes, and from their luminosity you can tell their mass. Based on the luminosity of UHZ1, it has a mass of about 40 million suns and possibly up to 70 million suns. The quasar has a redshift of z~10.3, which means we see it at a time when the universe was just 400 million years old. It was at the end of the Dark Ages of the Universe, when the first stars were just beginning to form. Somehow, UHZ1 has become super large in an extremely short amount of time. The gradual merging of stellar-mass black holes is unlikely to produce such a massive black hole on this time scale, or at least is unlikely. The authors are careful to note that with just one example of an early supermassive black hole, we shouldn’t jump to conclusions. But this is the best evidence for the heavy particle model.

References: Natarajan, P., et al. “First discovery of a supermassive black hole galaxy: UHZ1 – Evidence of a massive black hole seed from a direct collapse?” preprint arXiv arXiv:2308.02654 (2023).