New Gas Shuts Down Star Production in NGC 3226 Instead of Rejuvenating It

December 17, 2014

After it destroyed it’s neighbouring galaxy and took it’s gas and dust, the star production in NGC 3226 slowed down instead of being sped up by new material, making it a unique observation.

NGC 3226 with red central region where the star formation stopped and blue outer regions with young stars suggesting the galaxy was actively producing stars before acquiring a new material.

NGC 3226 with red central region where the star formation stopped and blue outer regions with young stars suggesting the galaxy was actively producing stars before acquiring a new material. Credit: NASA/CFHT/NRAO/JPL-Caltech/Duc/Cuillandre

Regular galaxies come in two variants - red elliptical galaxies full of old red stars and blue spiral galaxies where star formation is frequent, giving them the blue colour. Red galaxies have mostly depleted their gas and dust reserves needed for star formation, while blue galaxies still have plenty of juice in them.

It can happen for an old red galaxy to devour another galaxy and with newly acquired gas and dust to rejuvenate itself, begin to produce more stars again and start living it’s second youth. Recent study of the NGC 3226 galaxy 50 million light-years away shows a unique case where exactly the opposite happened.

Data from Hubble, Spitzer and Herschel telescopes show that NGC 3226 star birth rate actually declined because of the new material. For stars to form, dust and gas have to be cold. They have to cool enough to collapse under their own weight and form the star. When they are too hot, the particles are simply too far away. This is the problem that NGC 3226 is currently facing - new dust and gas particles are colliding with existing material in the galaxy, heating up the galaxy’s central region.

"We have explored the fantastic potential of big data archives from NASA's Hubble, Spitzer and ESA's Herschel observatory to pull together a picture of an elliptical galaxy that has undergone huge changes in its recent past due to violent collisions with its neighbuors," said Philip Appleton. He is the project scientist for the NASA Herschel Science Center at the California Institute of Technology, Pasadena, USA. "These collisions are modifying not only its structure and color, but also the condition of the gas that resides in it, making it hard -- at the moment -- for the galaxy to form many stars."

New gas and dust wouldn’t have been the problem if the supermassive black hole in the centre of NGC 3226 pulled the most of this new material to itself as supermassive black holes usually do. In this case, the majority of gas and dust are nowhere near the black hole.

"We are discovering that gas does not simply funnel down into the centre of a galaxy and feed the supermassive black hole known to be lurking there," Appleton said. "Rather, it gets hung up in a warm disk, shutting down star formation and probably frustrating the black hole's growth by being too turbulent at this point in time."

Sure, as the new material cools down, star will begin to form, but what is interesting here is that the blue colour in the outer regions of NGC 3226 suggests that the galaxy was already forming stars at some rate before the new material arrived and ruined the party for everyone. This is a unique observation that show’s a different scenario is possible.

"NGC 3226 will continue to evolve and may hatch abundant new stars in the future," said Appleton. "We're learning that the transition from young- to old-looking galaxies is not a one-way, but a two-way street."

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