The biggest black holes prevent star creation

Posted by Emma Woollacott

Scientists using the Herschel Space Observatory have discovered that galaxies with the most powerful, active black holes at their heart produce fewer stars.

All large galaxies are believed to contain supermassive black holes at their hearts. When gas falls upon them, it's accelerated and heated, releasing torrents of energy - and it's this that seems to be responsible.

"To understand how active galactic nuclei affect star formation over the history of the universe, we investigated a time when star formation was most vigorous, between eight and 12 billion years ago," says  James Bock, a senior research scientist at NASA's Jet Propulsion Laboratory.

"At that epoch, galaxies were forming stars 10 times more rapidly than they are today on average. Many of these galaxies are incredibly luminous, more than 1,000 times brighter than our Milky Way."

The team used Herschel data on 65 galaxies, observed in the far-infrared. These readings were compared with X-rays from the active central black holes in the galaxies, measured by NASA’s Chandra X-ray Observatory.

At lower intensities, they found, the black holes' brightness and star formation increased in sync. However, star formation dropped right off in galaxies with the most energetic central black holes.

The reason appears to be that when a black hole ingests too much, it starts releasing large amounts of radiation that prevents raw material from coalescing into new stars.

"Now that we see the relationship between active supermassive black holes and star formation, we want to know more about how this process works," says Bill Danchi, Herschel program scientist at NASA Headquarters in Washington.

"Does star formation get disrupted from the beginning with the formation of the brightest galaxies of this type, or do all active black holes eventually shut off star formation, and energetic ones do this more quickly than less active ones?"