... like I'm 5 years old
Think of a galaxy as a vast city of stars, with our own Sun being just one of the billions of stars in the Milky Way galaxy. But how do these starry cities form? It all starts with a large cloud of hydrogen gas and dust in space. Gradually, the force of gravity pulls this gas and dust together, causing it to begin rotating. As it rotates, the cloud collapses into a disc shape, with a bulge of material in the center.
The gas and dust in the disc start to clump together to form stars. The stars closest to the center of the disc form quickly and are older, while the stars on the outskirts of the disc form more slowly and are younger. This is how a spiral galaxy like our Milky Way forms. There are also other types of galaxies, such as elliptical galaxies, which form when two or more galaxies collide and merge together.
Imagine you're baking a pizza. You start with a ball of dough (the cloud of gas and dust) and as you spin it (the rotation), it flattens out into a disc (the galaxy). The toppings (the stars) are sprinkled all over the pizza, with more toppings in the center and fewer towards the edges.
... like I'm in College
The process of galaxy formation is governed by the laws of physics, particularly gravity. When the universe was very young, it was filled with a nearly uniform distribution of hydrogen and helium gas. However, tiny fluctuations in the density of this gas led to regions where the gas was slightly denser than its surroundings.
Gravity caused these denser regions to attract more and more gas, which eventually led to the formation of proto-galaxies. These were large, irregularly shaped clouds of gas, not yet the structured galaxies we see today. Inside these proto-galaxies, the gas continued to collapse under its own gravity, leading to the formation of stars.
The process of star formation also released a significant amount of energy, which pushed away the remaining gas in the proto-galaxy, preventing further star formation. This is why older galaxies have fewer young stars, as most of their gas was used up in the early stages of their formation.
Now imagine trying to explain galaxy formation with Lego bricks. Start with a large, flat baseplate – this represents the universe. Scatter a bunch of small, single-piece bricks (the hydrogen and helium atoms) all over the baseplate.
Now, take a handful of bricks and put them together into a larger structure – this represents a proto-galaxy, a denser region of the universe where gravity is pulling the gas together. Within this proto-galaxy, combine smaller bricks into larger structures – these represent stars forming from the gas.
Finally, place a large, unique Lego piece in the center of your proto-galaxy – this represents the supermassive black hole that forms at the center of most galaxies. The remaining pieces on the baseplate can represent other proto-galaxies in the universe, each with their own stars and black holes. Just like the real universe, this Lego universe is constantly evolving as new stars form and old ones die.
... like I'm an expert
The formation of galaxies is a complex process that involves many different physical phenomena, including gravity, hydrodynamics, thermodynamics, and nuclear physics. One important concept in our understanding of galaxy formation is the idea of dark matter halos. Dark matter is a hypothetical type of matter that doesn't interact with light but does have mass and can therefore exert a gravitational pull.
It is believed that galaxies form within these dark matter halos, with the gravity of the dark matter helping to pull the gas and dust together. The properties of the dark matter halo, such as its mass and size, can influence the properties of the galaxy that forms within it, such as its size and the number of stars it can form.
Another important factor in galaxy formation is the role of supermassive black holes. These black holes, which are found at the centers of most galaxies, can influence the formation of stars and the evolution of the galaxy as a whole.