Determining the exact complexity of structures in the universe can be a challenging task, and complexity itself can be subjective depending on the context. However, there are several notable structures in the universe that are considered highly complex. After the human brain, one of the most complex structures is often considered to be cosmic structures known as galaxy clusters.
Galaxy clusters are enormous systems consisting of hundreds or even thousands of galaxies held together by gravity. They can span several million light-years across and contain trillions of stars. Within these clusters, there are intricate interactions between galaxies, dark matter, hot gas, and other cosmic phenomena. The study of galaxy clusters involves understanding the complex dynamics, gravitational interactions, and the distribution of matter within them.
It is important to note that there might be other structures or systems in the universe that could be argued as more complex depending on different criteria and interpretations. The universe is vast and diverse, offering a plethora of intricate phenomena that scientists continue to explore and understand.