Galaxies Going Whump in the Night

Create Realms of Starbirth Light

Galaxy collisions fascinate me. And, they intrigue a growing number of astronomers who look at them with an eye toward understanding the processes at work when two or more of these cosmic behemoths interact with each other. One of my favorite galactic traffic-jam sites is Stephan’s Quintet, a visual grouping of five galaxies. Four of them are an actual compact group of galaxies in a sort of gravitational grouping. The additional galaxy appears in images of the group but it really lies much closer to us than the others and is not actually part of the group.  Here’s a recent image of it, and below that is a schematic diagram naming the pieces and parts of this galactic mingling.

Among the processes that get kick-started into motion when galaxies collide is star formation. The gravitational interactions create shock waves and compress the gases in the various galaxies together, and that in turn starts a wave of star formation. Astronomers often refer to this activity as “starburst activity”.

Take a look at any given galaxy interaction with starburst activity, and the bluish-colored blobs of light you see are more than likely the sites of starburst clumps.

The folks at Subaru Telescope in Hawai’i have released a three-dimensional view of Stephan’s Quintet. The observers used special narrowband filters on the telescope’s Suprime-Cam instrument that let very specific wavelengths of light emitted by ionized hydrogen (what they call hydrogen-alpha or H?). Think of H? as light that is emitted by hydrogen that is being heated by some process—like starbirth. Its presence traces the existence of star formation.

In addition to star-forming activity, the images created using the Subaru data help astronomers pinpoint more accurate distances to the galaxies. The contrasting images show that NGC7320 (the galaxy at the lower left) is closer than the other four  galaxies. It is about 50 million light-years away while the other four galaxies are about 300 million light-years away. This explains the intriguing arrangement of the galaxies in Stephan’s Quintet. And, it helps astronomers track the process of star formation during the collisions, and can also give them a clue of what to look for in other galaxy interactions where hot young stars will eventually be one of the by-products of the galactic traffic jam.

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