National Astronomical Observatory of Japan

Galactic Merger (II. The Case of Oblique Impact)


The Milky Way Galaxy in which we live and the neighboring Andromeda Galaxy are currently being drawn together through their mutual gravity. It is thought that they will collide in approximately another 4 billion years. This kind of collision between galaxies has actually been observed many times in the Universe. So what happens when galaxies collide? This video is a visualization of simulations performed with a supercomputer for the case of two spiral galaxies colliding obliquely.

Formation of Giant Star Clusters Resulting from a Galactic Collision

It’s called a galactic “collision,” but the individual stars within the galaxies don’t collide; they pass each other within the galaxies. But the gas filling the galaxies is compressed into strips where the galaxies collide, and clumps of thick gas form in these regions. Stars form explosively within these gas clouds, and these stars collect to create giant star clusters. Then the two galaxies move past each other, dragging along the star clusters formed by the collision.

But before long, the two galaxies are pulled back towards each other by their mutual gravity and collide again. And finally they become a single large galaxy. Around the galaxy formed by this merger there are large star clusters which were formed in the first collision. From this simulation we learned that galactic mergers form a far larger mass of star clusters than previously thought.

Translation by: Ramsey Lundock (NAOJ)

Video Data

ComputerCray XT-4
Number of Particles Used in CalculationsDark Matter 2.8 x 107; Baryons 2.3 x 106
Phenomenon Time Scale1,000,000,000 years
Phenomenon Spatial Scale500,000 light-years
Simulation byHidenori Matsui (NAOJ)
CreditSimulation: Hidenori Matsui, Visualization: Takaaki Takeda, Four-Dimensional Digital Universe Project, NAOJ

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