Principles behind galaxy formation

In summary, the formation of galaxies is a result of gravity pulling matter together. However, friction plays a crucial role in slowing down particles and allowing them to form clusters. Quantum fluctuations in the early universe also contributed to the formation of these clusters. It appears that gas and dust are more likely to form galaxies due to their ability to be slowed down by friction, while randomly distributed rocks have less chance of colliding and forming clusters.
  • #1
jostpuur
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When things are kept at the simplest, I've heard that galaxies were formed because gravity pulls stuff together, but there's some things that are not fully making sense. If two objects are far away, and they get attracted by gravity, what happens is that they merely pass each others with some great velocity and fly far away again, according to the conservation of energy. So what is it really that makes clusters start forming out of homogeneous matter then?
 
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  • #2
jostpuur said:
When things are kept at the simplest, I've heard that galaxies were formed because gravity pulls stuff together, but there's some things that are not fully making sense. If two objects are far away, and they get attracted by gravity, what happens is that they merely pass each others with some great velocity and fly far away again, according to the conservation of energy. So what is it really that makes clusters start forming out of homogeneous matter then?

Supposedly, quantum fluctuations in the early universe provided the seeds for (clusters of) galaxy formation. This an Interesting story that I don't understand fully.

https://www.physicsforums.com/showthread.php?t=246423

https://www.physicsforums.com/showthread.php?p=1818318#post1818318
 
  • #3
jostpuur said:
When things are kept at the simplest, I've heard that galaxies were formed because gravity pulls stuff together, but there's some things that are not fully making sense. If two objects are far away, and they get attracted by gravity, what happens is that they merely pass each others with some great velocity and fly far away again, according to the conservation of energy. So what is it really that makes clusters start forming out of homogeneous matter then?

You are neglecting friction in this scenario. As gas and dust collapse under the influence of gravity the particles collide more and more frequently as the density increases. Thus a lot of the kinetic energy is radiated away as heat leaving the particles moving more slowly than otherwise. Provided there is enough inhomogenaity to start with, friction does the rest.
 
  • #5
The story about formation of original irregularities after big bang wasn't precisely what I was after, although that seems to be another interesting story too. I was wandering, that even if there is some irregularities to start with, how can gravity start causing clusters to emerge, when matter should be flying far away after first coming close to some other matter. I suppose the answer is the friction mentioned by paw then.

Am I correct to guess that galaxies could not start forming out of randomly distributed pieces of rocks in the space, as easily as they start forming out of gas and dust? Because pieces of rocks have less chance of colliding, they just fly in hyperbola trajectories by each others? Gas and dust instead gets slowed down by friction more easily?
 

What is the Big Bang theory and how does it relate to galaxy formation?

The Big Bang theory is the widely accepted explanation for the origins of the universe. It states that about 13.8 billion years ago, all matter and energy in the universe was compressed into an incredibly dense and hot state. This state then expanded rapidly, resulting in the formation of galaxies and other structures. The Big Bang theory is closely related to galaxy formation because it explains the initial conditions of the universe that led to the formation of galaxies.

What role do dark matter and dark energy play in galaxy formation?

Dark matter and dark energy are two mysterious components that make up about 95% of the total mass and energy of the universe. While their exact nature is still unknown, scientists believe that dark matter played a crucial role in the formation of galaxies by providing the gravitational pull necessary for gas and dust to come together and form stars. Dark energy, on the other hand, is thought to be responsible for the accelerating expansion of the universe, which has a significant impact on the formation and evolution of galaxies.

What are the main processes involved in galaxy formation?

The main processes involved in galaxy formation are gravitational collapse, gas accretion, and mergers. Gravitational collapse occurs when the density of matter in a region becomes high enough to overcome the outward pressure and pull the matter together. Gas accretion is the process by which gas from the surrounding environment is pulled into the galaxy, providing the fuel for star formation. Mergers happen when two or more galaxies collide and merge, resulting in the formation of a larger, more massive galaxy.

How do the properties of a galaxy, such as size and shape, relate to its formation?

The properties of a galaxy, such as its size and shape, are closely related to its formation history. For example, larger galaxies are thought to have formed through the merging of smaller galaxies, while smaller galaxies may have formed through the gradual accretion of gas and dust. The shape of a galaxy also reflects its formation history, with spiral galaxies being the result of more orderly gas accretion and elliptical galaxies being the product of mergers.

What advancements in technology have helped us better understand the principles behind galaxy formation?

Advancements in technology, such as telescopes and computer simulations, have greatly contributed to our understanding of galaxy formation. Telescopes allow us to observe and study galaxies in detail, providing valuable data and insights into their formation. Computer simulations, on the other hand, allow scientists to model and study the complex physical processes involved in galaxy formation, helping us refine and improve our understanding of the principles behind it.

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