What are galaxies?Galaxies are collections of stars, gas, dust, and other compact objects like planets embedded within an extended dark matter halo. Each of the tens of billions of galaxies in the universe are all unique and different from one another but can be generally classified according to their shapes, gas content, stellar content, star formation properties, and many other criteria. From this diversity, it is clear that the growth histories of galaxies can vary substantially from one another. Extragalactic astrophysicists have the challenging task of trying to understand where this diversity comes from and what physical mechanisms were important in the formation and evolution of galaxies.
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How do we study galaxies?There are two general approaches to studying galaxies: observations and simulation modeling. Observations across all wavelengths of light using telescopes both on the ground and in space allow us to analyze and attempt to interpret the actual light coming from galaxies. This can be done via archeological studies - where a few galaxies are analyzed in fine detail - or survey studies - where large populations of galaxies are studied to understand overall trends and correlations. Simulation modeling is the computational endeavor to try to replicate the properties of real galaxies using the physics that we think is important for their growth. In other words, galaxy formation models are laboratories in which to test our physical understanding of why galaxies are the way they are. Using these two approaches in tandem is essential since the success or failure of simulation modeling to reproduce what is seen in observations can tell us an enormous amount about whether we’re on the right track or not when it comes to understanding the physics that governs galaxy growth.
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