Colliding galaxies cause incredibly bright starbust inside cloak of dust

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Two distant spiral galaxies are merging together, and behind a shroud of dust is a frenzy of star formation. This single region emits more infrared light than an entire galaxy, and is ten times brighter than anything else like it.

Although galaxy collisions are dramatic events on a large scale, individual stars aren't usually affected. Even in the most densely packed parts of a galaxy, there's still a trillion miles separating one star from another, leaving plenty of room for galaxies to merge together without stars and planets being put in harm's way.

Dust and gas clouds are a different story. They are vast enough to make at least a handful of collisions likely, and when they smash together they cause the gravitational collapse of any dense pockets of matter that might be around them. This in turn creates a generation of new stars, which emit massive, intense bursts of ultraviolet radiation. In this particular case, however, the dust cloud that covers this region redirects the light into the infrared spectrum.


Known as starbursts, these phenomena generally only occur near the center of galaxies where more raw materials are concentrated, by the collision of two dust clouds can recreate those star-forming conditions far away from either galaxy's center.

That's what's happening here as the pair of galaxies that make up II Zw 096 slowly merge together. The starburst region is only about 700 light-years across, paltry compared to the galaxies' full length of about 50,000 to 60,000 light-years. Even so, the star-forming region accounts for 80 percent of the infrared light emitted by both galaxies. The starburst is cranking out about 100 solar masses worth of stars every single year, the equivalent of producing 100 copies of our Sun every year.


This event has shocked its discoverers at the Spitzer Space Telescope, who never expected to find something so bright so far away from a galactic center. Astronomer and chief researcher Hanae Imani explains:

"This discovery proves that merging galaxies can generate powerful starbursts outside of the centers of the parent galaxies. The infrared light emission of the starburst dominates its host galaxy and rivals that of the most luminous galaxies we see that are relatively close to our home, the Milky Way. Most of the far-infrared emission in II Zw 096, and hence most of the power, is coming from a region that is not associated with the centers of the merging galaxies. This suggests that the appearances and interactions of distant, early galaxies during epochs when mergers were much more common than today in the Universe might be more complicated than we think."


[The Astronomical Journal]