The Dance of the Galaxies

Hubble Sees It

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.

The collision of a pair (or more) of galaxies begins long before they look like they’re actually touching. The gravitational influence of both galaxies begins to pull shreds of galaxy parts (gas, dust, stars). It also starts to distort the shape of the galaxies doing the interacting. If you look closely at this pair you’ll see some part of the lower galaxy is being pulled toward the “upper” galaxy. There are also little blue clouds out to either side of the galaxy. Most likely those are star-forming regions, so-called “starburst” knots that are ignited during galaxy interactions. (There are also other galaxies in the picture — see if you can spot them all.)  As things proceed, you start to see definite “shredding” effects as the shockwaves of collision distort the galaxies.

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.

You can see the other 57 galaxy interactions here. Be prepared for quite a fascinating tour! It’s amazing what can happen when some of the biggest structures in the universe do a little cosmic dance with each other!