It Turns Out They Do… All Over the Place
Back before astronomers had high-resolution cameras and spectrographs and orbiting spacecraft to look at the distant universe, interacting galaxies were just plain weird. They didn’t fit into the standard scheme of galaxies as set out by the venerable giant of astronomy, Edwin Hubble. Every astronomer worth his (and sometimes a few “her”) salt memorized the Hubble tuning fork diagram and tried to fit every galaxy observed somewhere in this hierarchy.
Trouble is, not all galaxies “played the game.” Some of them looked downright pathological, twisted up, or misshapen or something. But the problem was that until we could look at these galactic weirdos with good optics and high-resolution spectrographs, astronomers couldn’t really tell what was going on with many of them.
That’s why the monumental set of galaxies that Hubble Space Telescope and other high-resolution ground-based observatories have observed over the years is such a great achievement. For the first time, astronomers can see what’s happening. And, they’re finding galaxy interactions (collisions, if you will) all over the place. The fact that we’re seeing them nearly everywhere we point a telescope to tells us that collisions aren’t just oddball occurrences in the universe. They’re part of an evolutionary process that shapes galaxies and triggers star formation in the process.
Our own Milky Way is actually cannibalizing smaller galaxies as you read this. The Sloan Digital Sky Survey is tracing out the streams of stars that are pouring into our galaxy as these smaller galaxies interact with the Milky Way. Here’s what it looks like from our vantage point inside the Milky Way.
Galaxy interaction is a hot topic in astronomy these days as the folks researching these cosmically titanic events dig into the details. Stay tuned!
Hubble Space Telescope has been peering out at galaxies (and all kinds of other objects in the cosmos) since 1990. Over the years it has captured many views of galaxies interacting. By interacting, I mean that they come together, they collide, they mingle stars and clouds of gas and dust, and then in the aftermath, new stars are formed. The view from a distance is breathtaking. Like this one. The combined galaxy interaction is named NGC 5331, and they lie about 450 million light-years away from us in the direction of the constellation Virgo.
To celebrate the 18th anniversary of Hubble’s launch (gad, has it been 18 years already?), the Space Telescope Science Institute and the Hubble ESA folks have released an image collection of 59 galaxy interactions. Here’s another one — the interacting galaxy pair that makes up Arp 148. This one shows the pair well after the collision (interaction) began. The blue “ring-shaped” object is a collection of matter ejected by the shockwave generated during the collision. It’s blue because the shock also touched off a burst of star formation. Those are hot, young blue stars there, just beginning their lives in the chaos of a galaxy collision.