Joshua E. Barnes (Institute for Astronomy, University of Hawaii)

What happens when two galaxies merge? The answer to this question lies in the mass of each galaxy. If one galaxy is significantly larger and more massive than the other, the smaller galaxy could become completely absorbed by the larger one. If the masses are comparable, a number of outcomes are possible. The galaxies may pass right through one another, remaining, for the most part, intact as separate gravitational entities (albeit disrupted). Often these two galaxies will collide again, either forming a new structure from the merger or becoming two dwarf galaxies that are a fraction of their original sizes.

What happens inside a merging galaxy?

Inside galaxies, stars are relatively far apart. Therefore, when galaxies collide, the likelihood of the individual stars colliding are minimal. However, what fills the space between the stars is the gas and dust of the galaxy. When these clouds of gas and dust collide with one another, a great deal of turbulence is created which disrupts the gas clouds. As the particles are forced together at high speeds, areas of extreme pressure are created. These active pockets will eventually explode into regions of renewed stellar birth.

The Simulation

This simulation demonstrates a merging of two gas-rich disk galaxies. Only the gas particles are shown. The colors indicate the energy dissipated by shocks arising from the collision (blue is lower energy). Ultimately, the galaxies merge into one body giving birth to new star-forming regions and a new galaxy.

Eve Klein