The Cosmic Dance

Galactic Minuets

Yesterday I talked about galaxy mergers and acquisitions, the subject of my latest segment on These scenes fascinate me because galaxies are not exactly tiptoing through the tulips as they interact with each other.

Think of the sheer amount of mass involved!  For the Milky Way, you’re talking about the mass of what, somewhere between 300-400 billion stars.  If every star in the galaxy had the same mass as the Sun — which has a mass of 1.9 x 1030 kilograms — you’re talking about a LOT of mass. Of course, not every star is the mass of the Sun — some are more massive, some are less massive. And, of course, we have that pesky massive black hole at the center, and huge amounts of interstellar gas and dust also poking around the space lanes.

When two galaxies interact, however, that mass doesn’t all clash together in a huge crash.  Stars aren’t necessarily colliding with each other, although the action of the merger does compress the interstellar gas and dust, and sets off waves of star formation. But, all of that mass exerts a gravitational influence, which is the main “actor” in a galaxy collision.  That influence is what tears out streams of gas and dust from interacting galaxies, and reshapes the morphology (the shape) of all the galaxies doing the interacting.  While a galaxy interaction may look graceful in the images we see from HST and Spitzer and other observatories, it’s quite a massive and impressive undertaking.

To understand how these collisions and interactions take place, astronomers are creating impressive computer models. These get turned into animations that allow us to follow the galactic dance from start to finish, many many times faster than it happens in real life.  I used one from a scientist named John Dubinksi in my segment (see it below) to show the upcoming Milky Way/Andromeda Galaxy interaction, which will happen in our far future. Check it out!  And, head over to to see the rest of this month’s space news show!

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