Supermassive black holes (SMBHs) can reach extraordinary sizes in the universe. While there is no strict upper limit, they are generally found to have masses ranging from millions to billions of times the mass of our Sun. The largest known supermassive black hole, residing in the center of the galaxy Holmberg 15A, has a mass estimated to be around 40 billion solar masses.
The formation process of supermassive black holes is not yet fully understood. There are two primary hypotheses regarding their origins:
Accretion and Growth: This hypothesis suggests that supermassive black holes form through the gradual accretion of mass over long periods of time. Initially, small black holes or stellar-mass black holes (formed from the collapse of massive stars) are present. Through various mechanisms such as mergers with other black holes and the accretion of surrounding matter (gas, dust, and other stars), these black holes grow in size over billions of years, eventually becoming supermassive.
Direct Collapse: Another hypothesis proposes that supermassive black holes can form directly from the collapse of enormous clouds of gas in the early universe. These gas clouds, with sufficient mass and conditions, collapse directly into a massive black hole without going through the intermediate stages of stellar black holes. This process would allow supermassive black holes to form relatively quickly, within millions of years.
Determining which of these hypotheses (or a combination of both) is more prevalent in the formation of supermassive black holes is an active area of research, and scientists continue to investigate and refine our understanding of their origins.
It's important to note that the timescale for the formation of supermassive black holes can vary depending on the formation mechanism and the availability of mass for accretion. The formation process is likely to occur over long cosmic timescales, potentially ranging from tens of millions to billions of years.
Understanding the formation and growth of supermassive black holes is a complex and fascinating field of study that involves observations, simulations, and theoretical modeling. Ongoing research aims to shed more light on the specific mechanisms responsible for the existence and properties of these remarkable cosmic objects.