A twisted starburst galaxy

A spectacular new picture of the nearby starbursting galaxy NGC 1313, taken by the Gemini Observatory, shows giant regions of intense star formation whose origin are still a mystery.

The mysterious starburst galaxy NGC 1313. Image: Gemini Observatory/AURA/Travis Rector (University of Alaska, Anchorage).

NGC 1313 is a barred spiral galaxy 15 million light years away in the Southern Hemisphere constellation of Reticulum. Bubbles of interstellar gas, ripples and shock fronts from violent supernovae, and brilliant clusters of massive stars light up its 50,000 light year extent, but there is no explanation for all this activity. Usually when a galaxy enters starburst, it is because its gas has been stirred up by a gravitational interaction with a neighbouring galaxy, but NGC 1313 is a loner, drifting through empty space away from packs of other galaxies. The central stellar bar cannot be to blame either; although in other galaxies bars are often the focus of much star formation, in the case of NGC 1313 the majority of the action is taking place along the edges of the oddly twisted and asymmetric spiral arms.

Equally mysterious is an enormous ‘superbubble’; a cavity within the galaxy’s interstellar gas that has disconnected some of the star-forming regions on the right of the picture. The edge of this bubble is causing gas to pile up and form stars.

“What triggered the superbubble is still a mystery,” says Dr Stuart Ryder of the Anglo–Australian Observatory. “It would have required a thousand supernovae to go off in the space of just a few million years, or else something punched its way through the disc and set it off like ripples in a pond.”

The Gemini image used narrowband filters to better capture the light of gas ionised by the intense star formation. Red indicates ionised hydrogen, blue reveals helium and green points to oxygen. The star-forming regions are evident as the fiery-coloured areas.