Retro/prograde flyby galaxies and their bar formation

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In summary, the study of retro/prograde flyby galaxies explores the interactions between galaxies that pass by each other in opposite or similar directions. These encounters can significantly influence the structure and dynamics of the galaxies involved, often leading to the formation of bars—elongated structures of stars and gas. The gravitational interactions during these flybys can induce instabilities that trigger the bar formation process, altering the galaxies' morphology and star formation activity. Understanding these phenomena provides insights into the evolution of galactic systems and the role of gravitational dynamics in shaping their characteristics.
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milkism
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TL;DR Summary
In fast flyby encounters, typically involving a smaller or equal in mass galaxy (secondary) passing by a relatively stationary galaxy (primary), a bar formation can occur in either the secondary galaxy or both galaxies. This depends on their masses and their relative motions (whether prograde or retrograde).
https://iopscience.iop.org/article/10.1088/2041-8205/790/2/L33/pdf

In section 3, it states that during a 1:1 prograde passage, bar formations are visible in both galaxies, whereas in the retrograde version, there are no bar formations in either galaxy. I would like to understand the physics behind this.

My initial thought is as follows:

During a 1:1 retrograde passage, the gravitational interactions of both galaxies are equal in magnitude, but their signs differ. Therefore, if we sum up all the gravitational forces, the net effect would be zero.

Is this partially correct (of course, aside from gravitational forces, there are other factors too) or am I completely wrong?
 
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milkism said:
a relatively stationary galaxy (primary)
Do you think there is any significance of a reference frame in which one of the galaxies is 'relatively stationary'?

milkism said:
I would like to understand the physics behind this.
If the physics was easy to understand we wouldn't need to spend thousands of hours of CPU time performing simulations.

milkism said:
During a 1:1 retrograde passage, the gravitational interactions of both galaxies are equal in magnitude, but their signs differ.
Yes, according to Newton's third law. How is this different in a prograde passage?

milkism said:
Is this partially correct
I don't think so. Galaxy flybys may cause perturbations in galaxy structure due to the gravitational attraction of individual stars towards the "other" galaxy. In a prograde flyby individual stars are closer to the other galaxy for much longer than in a retrograde flyby (similar to the difference between a car overtaking you and a car passing in the opposite direction) so this attraction has a much greater effect.
 

FAQ: Retro/prograde flyby galaxies and their bar formation

What are retrograde and prograde flyby galaxies?

Retrograde and prograde flyby galaxies refer to the relative motion of galaxies as they pass by one another. A prograde flyby occurs when two galaxies move in the same direction during their encounter, while a retrograde flyby happens when they move in opposite directions. These interactions can significantly influence the structure and dynamics of the galaxies involved.

How do retro/prograde flybys affect bar formation in galaxies?

During a flyby interaction, gravitational forces can induce tidal interactions that may lead to the formation of bars in galaxies. Prograde flybys tend to enhance the density of stars and gas in certain regions, promoting bar formation. Conversely, retrograde encounters may lead to more complex interactions that can also trigger bar formation but through different mechanisms, such as angular momentum transfer and redistribution of material.

What is the significance of bar formation in galaxies?

Bar formation in galaxies is significant because it alters the dynamics and structure of the galaxy. Bars can funnel gas towards the central regions, potentially fueling star formation and active galactic nuclei (AGN). They also influence the orbits of stars and can lead to the redistribution of angular momentum, affecting the overall evolution of the galaxy.

Are there observational methods to study retro/prograde flyby galaxies?

Yes, astronomers use various observational methods to study retro/prograde flyby galaxies, including multi-wavelength imaging and spectroscopy. Observations in optical, infrared, and radio wavelengths help identify the morphology, star formation rates, and kinematics of galaxies involved in flybys. Additionally, simulations and models can be compared with observational data to understand the effects of these interactions better.

What role do simulations play in understanding retro/prograde flyby galaxies?

Simulations are crucial for understanding the dynamics of retro/prograde flyby galaxies. They allow scientists to model the gravitational interactions and predict the outcomes of such encounters over time. By varying parameters like mass, velocity, and orientation, simulations help in exploring different scenarios and provide insights into the mechanisms behind bar formation and the resulting morphological changes in the galaxies.

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