The gravitational pull between galaxies is the dominant force that initiates and governs their interactions.

Tidal interactions, where galaxies distort each other's shapes due to gravitational forces, are the most prevalent form of galaxy interaction.

In a head-on collision, the galaxies' gravitational forces pull them together, leading to a merger and the formation of a single, larger galaxy.

Accretion is the process by which a smaller galaxy is gradually pulled in and absorbed by a larger galaxy, increasing the latter's mass and size.

Tidal tails are elongated streams of stars and gas that are pulled out of galaxies during interactions due to the gravitational forces exerted by the interacting galaxies.

The Milky Way galaxy is believed to have merged with the Sagittarius dwarf galaxy, contributing to its mass and shaping its structure.

The Milky Way and Andromeda galaxies are on a collision course and are expected to merge in approximately 4 billion years, resulting in a single, larger galaxy.

Sagittarius A* is the supermassive black hole located at the center of the Milky Way galaxy, with a mass of approximately 4 million times that of the Sun.

Andromeda A* is the supermassive black hole at the center of the Andromeda galaxy, with a mass estimated to be between 100 million and 1 billion times that of the Sun.

The elliptical galaxy M87 is not the result of a merger, but rather formed through a different process involving the collapse of a large gas cloud.

The spiral galaxy M51 is not the result of a merger, but rather formed through a different process involving the accretion of gas and stars.

The barred spiral galaxy NGC 1365 is not the result of a merger, but rather formed through a different process involving the interaction of gas and stars within the galaxy.

The irregular galaxy NGC 4449 is not the result of a merger, but rather formed through a different process involving the interaction of gas and stars within the galaxy.

The lenticular galaxy NGC 3115 is not the result of a merger, but rather formed through a different process involving the interaction of gas and stars within the galaxy.

The dwarf galaxy NGC 1705 is not the result of a merger, but rather formed through a different process involving the interaction of gas and stars within the galaxy.