The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, clustering and merging allows galaxies to accumulate mass, determining both their shape and structure. Hydrodynamics simulation, which simulates both baryons and dark matter, is widely used to study galaxy formation and evolution.
In physical cosmology, a protogalaxy, which could also be called a "primeval galaxy", is a cloud of gas which is forming into a galaxy. It is believed that the rate of star formation during this period of galactic evolution will determine whether a galaxy is a spiral or elliptical galaxy; a slower star formation tends to produce a spiral galaxy. The smaller clumps of gas in a protogalaxy form into stars.
The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components:
- a cosmological constant, denoted by lambda (Λ), associated with dark energy
- the postulated cold dark matter, denoted by CDM
- ordinary matter
In modern models of physical cosmology, a dark matter halo is a basic unit of cosmological structure. It is a hypothetical region that has decoupled from cosmic expansion and contains gravitationally bound matter. A single dark matter halo may contain multiple virialized clumps of dark matter bound together by gravity, known as subhalos. Modern cosmological models, such as ΛCDM, propose that dark matter halos and subhalos may contain galaxies. The dark matter halo of a galaxy envelops the galactic disc and extends well beyond the edge of the visible galaxy. Thought to consist of dark matter, halos have not been observed directly. Their existence is inferred through observations of their effects on the motions of stars and gas in galaxies and gravitational lensing. Dark matter halos play a key role in current models of galaxy formation and evolution. Theories that attempt to explain the nature of dark matter halos with varying degrees of success include cold dark matter (CDM), warm dark matter, and massive compact halo objects (MACHOs).
In physical cosmology, structure formation describes the creation of galaxies, galaxy clusters, and larger structures starting from small fluctuations in mass density resulting from processes that created matter. The universe, as is now known from observations of the cosmic microwave background radiation, began in a hot, dense, nearly uniform state approximately 13.8 billion years ago. However, looking at the night sky today, structures on all scales can be seen, from stars and planets to galaxies. On even larger scales, galaxy clusters and sheet-like structures of galaxies are separated by enormous voids containing few galaxies. Structure formation models gravitational instability of small ripples in mass density to predict these shapes, confirming the consistency of the physical model.
The Millennium Run, or Millennium Simulation is a computer N-body simulation used to investigate how the distribution of matter in the Universe has evolved over time, in particular, how the observed population of galaxies was formed. It is used by scientists working in physical cosmology to compare observations with theoretical predictions.
Carlos Silvestre Frenk is a Mexican-British cosmologist. Frenk graduated from the National Autonomous University of Mexico and the University of Cambridge and spent his early research career in the United States, before settling permanently in the United Kingdom. He joined the Durham University Department of Physics in 1986 and since 2001 has served as the Ogden Professor of Fundamental Physics at Durham University.
Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies involved, but the exact effects of such mergers depend on a wide variety of parameters such as collision angles, speeds, and relative size/composition, and are currently an extremely active area of research. Galaxy mergers are important because the merger rate is a fundamental measurement of galaxy evolution and also provides astronomers with clues about how galaxies grew into their current forms over long stretches of time.
GADGET is free software for cosmological N-body/SPH simulations written by Volker Springel at the Max Planck Institute for Astrophysics. The name is an acronym of "GAlaxies with Dark matter and Gas intEracT". It is released under the GNU GPL. It can be used to study for example galaxy formation and dark matter.
Simon David Manton White, FRS, is a British-German astrophysicist. He was one of directors at the Max Planck Institute for Astrophysics before his retirement in late 2019.
George Petros Efstathiou is a British astrophysicist who is Professor of Astrophysics (1909) at the University of Cambridge and was the first director of the Kavli Institute for Cosmology at the University of Cambridge from 2008 to 2016. He was previously Savilian Professor of Astronomy at the University of Oxford.
The Institute for Computational Cosmology (ICC) is a research institute at Durham University, England. It was founded in November 2002 as part of the Ogden Centre for Fundamental Physics, which also includes the Institute for Particle Physics Phenomenology (IPPP). The ICC's primary mission is to advance fundamental knowledge in cosmology. Topics of active research include: the nature of dark matter and dark energy, the evolution of cosmic structure, the formation of galaxies, and the determination of fundamental parameters.
The Bolshoi simulation, a computer model of the universe run in 2010 on the Pleiades supercomputer at the NASA Ames Research Center, was the most accurate cosmological simulation to that date of the evolution of the large-scale structure of the universe. The Bolshoi simulation used the now-standard ΛCDM (Lambda-CDM) model of the universe and the WMAP five-year and seven-year cosmological parameters from NASA's Wilkinson Microwave Anisotropy Probe team. "The principal purpose of the Bolshoi simulation is to compute and model the evolution of dark matter halos, thereby rendering the invisible visible for astronomers to study, and to predict visible structure that astronomers can seek to observe." “Bolshoi” is a Russian word meaning “big.”
The Illustris project is an ongoing series of astrophysical simulations run by an international collaboration of scientists. The aim is to study the processes of galaxy formation and evolution in the universe with a comprehensive physical model. Early results were described in a number of publications following widespread press coverage. The project publicly released all data produced by the simulations in April, 2015. Key developers of the Illustris simulation have been Volker Springel and Mark Vogelsberger. The Illustris simulation framework and galaxy formation model has been used for a wide range of spin-off projects, starting with Auriga and IllustrisTNG followed by Thesan (2021), MillenniumTNG (2022) and TNG-Cluster (2023).
Benedetta Ciardi is an Italian astrophysicist.
Claudia Maraston is a Professor of Astrophysics at the University of Portsmouth. She designs models for the calculation of spectro-photometric evolution of stellar populations. She is the winner of the 2018 Royal Astronomical Society Eddington Medal.
The UniverseMachine is a project carrying out astrophysical supercomputer simulations of various models of possible universes, created by astronomer Peter Behroozi and his research team at the Steward Observatory and the University of Arizona. Numerous universes with different physical characteristics may be simulated in order to develop insights into the possible beginning and evolution of our universe. A major objective is to better understand the role of dark matter in the development of the universe. According to Behroozi, "On the computer, we can create many different universes and compare them to the actual one, and that lets us infer which rules lead to the one we see."
Barbara Sue Ryden is an American astrophysicist who is a Professor of Astronomy at Ohio State University. Her research considers the formation, shape and structure of galaxies. She was elected a fellow of the American Association for the Advancement of Science in 2016.
Hsiao-Wen Chen is a Taiwanese-American astronomer who uses a combination of absorption spectroscopy and emission-line mapping to study diffuse baryonic "normal matter" in the intergalactic medium and galactic halos, and the connections between this matter and the matter in star-forming regions of galaxies. The circumgalactic medium resides in the interface between star-forming regions and intergalactic space contains the majority of baryonic mass as well as the critical record of gas circulation in and out of galaxies. Chen, a professor of astronomy and astrophysics at the University of Chicago, has been leading efforts to decipher how the growth and evolution of galaxies over cosmic time are connected and/or regulated by the physical properties of the circumgalactic gas.
Debora Šijački is a computational cosmologist whose research involves computational methods for simulating the formation and development of the structures in the universe including galaxies, galaxy clusters, and dark matter, including collaborations in the Illustris project. Originally from Serbia, she was educated in Italy and Germany, and works in the UK as a professor at the University of Cambridge and deputy director of the Kavli Institute for Cosmology.
Canada: University of Victoria 
Chile: University of La Serena 
China: National Astronomical Observatories of China 
Finland: University of Helsinki 
Germany: Max Planck Institute for Astrophysics and Leibniz Institute for Astrophysics Potsdam 
United Kingdom: Durham University, Liverpool John Moores University, University of Manchester, University of Nottingham and University of Sussex 
United States: Johns Hopkins University and UC Riverside 
