Black holes not guilty of shutting down star formation

January 22nd, 2009 - 12:22 pm ICT by ANI  

Washington, Jan 22 (ANI): A team of astronomers from Yale University has found evidence that indicates black holes are not responsible for shutting down star formation.

They discovered that galaxies stop forming stars long before their central supermassive black holes reach their most powerful stage.

Until recently, astronomers believed that active galactic nuclei (AGN), the supermassive, extremely energetic black holes at the centers of many young galaxies, were responsible for shutting down star formation in their host galaxies once they grew large enough.

It was thought that AGN feed on the surrounding galactic material, producing enormous amounts of energy (expelled in the form of light) and heat the surrounding material so that it can no longer cool and condense into stars.

But, new research shows that this shutting-down process appears to take place much earlier in the AGNs lifetime, well before it starts shining brightly.

This high-luminosity phase, when the AGN are at their biggest and brightest and most powerful, is not the phase responsible for the shutdown of star formation, said Kevin Schawinski, a postdoctoral associate in Yales astronomy department and lead author of the study.

The researchers analyzed images of 177 galaxies taken by two different space telescopes to create a comprehensive view of galaxies with AGN, including ones where the AGN were both obscured by the galaxys dust and gas, and ones where there was an unobstructed view of the AGN from the Earths vantage point.

Until now, some astronomers believed they cant see AGN in any galaxies that are still actively forming stars simply because the light from the AGN is obscured by the galaxys gas and dust.

Schawinski and his team are the first to show that in fact there are no bright AGN at the centers of star-forming galaxies.

By subtracting out the light from the AGN, the team discovered that all of the galaxies with bright AGN had stopped forming stars several hundred million years earlier.

The key result is the finding that there is a lack of AGN in galaxies that are currently forming stars, said Meg Urry, head of the Yale team and director of the Yale Center for Astronomy and Astrophysics. That tells us the AGN doesnt turn on until long after the stars stop forming, Urry added.

As for the real culprit, responsible for shutting down star formation, its possible that an earlier, low-luminosity phase is responsible, said Schawinski.

Either way, this result shows that our previous understanding of how the shutting-down process works wasnt as simple as we thought, he added. (ANI)

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