Overfed black holes shut down galactic star-making, says new study involving CU-Boulder


Galaxies with the most powerful, active black holes at their cores produce fewer stars than galaxies with less active black holes, according to a new study involving the University of Colorado Boulder using the Herschel Space Observatory.

The results from Hershel, a European Space Agency-led mission involving NASA, demonstrate that black holes suppressed galactic star formation when the universe was less than half its current age. The team made observations with the Spectral and Photometric Imaging Receiver, or SPIRE instrument, onboard Herschel, said CU-Boulder Professor Jason Glenn, a co-author on the study.

“We want to know how star formation and black hole activity are linked,” said Mathew Page of University College London’s Mullard Space Science Laboratory in the United Kingdom, lead study author. “The two processes increase together up to a point, but the most energetic black holes appear to turn off star formation.”

A paper on the subject involving more than two dozen institutions is being published in the May 10 issue of Nature. CU-Boulder is receiving more than $2 million from NASA’s Jet Propulsion Laboratory in Pasadena for the combined support of SPIRE instrument development and science data analysis during the lifetime of the orbiting telescope.

Previous studies of nearby galaxies have suggested that active, massive black holes in the centers of galaxies can quench star formation as they heat up and eject energy, dispersing the reservoirs of cold gas that are required to create new stars. But the relationship of giant, luminous black holes -- known as active galactic nuclei -- to star formation has been unclear, Glenn said.

“By using data from Herschel, we now have the first direct evidence that the larger, more energetic black holes were quenching star formation billions of years ago,” said Glenn of CU-Boulder’s astrophysical and planetary sciences department. “The study shows a correlation between the amount of black hole accretion -- essentially the amount of material falling into it -- and the limiting of star formation.”

Supermassive black holes, with masses as large as many millions of suns, are believed to reside in the hearts of all large galaxies. When gas and dust fall into them, the matter is accelerated and heated, releasing great torrents of energy. Earlier in the history of the universe, these objects were often much brighter and more energetic, and star formation also was livelier back then, according to the research team.

The team used Herschel to observe 65 distant galaxies thought to be between 8 billion and 12 billion years old -- a time when galaxies were forming stars at about 30 to 100 times the current rate and when some galaxies were more than 1,000 times brighter than our Milky Way. Made in the far infrared portion of the electromagnetic spectrum with SPIRE, the observations were part of the Herschel Multi-tiered Extragalactic Survey, or HerMES, which involves more than 100 astronomers from six countries, including Glenn.

The bulk of the energy released by developing stars in the observed galaxies was in the form of visible and ultraviolet light that was absorbed by surrounding dust clouds, making it invisible to most telescopes, said Glenn, also a fellow at CU-Boulder’s Center for Astrophysics and Space Astronomy. But the heated dust clouds around the developing stars were observed by SPIRE to glow in the far infrared, or submillimeter wavelengths, allowing astronomers to estimate rates of star formation.

Herschel is the first space observatory to make high-resolution images at submillimeter wavelengths, which are longer than visible and infrared light waves and shorter than radio waves, said Glenn. SPIRE was designed to look for emissions from clouds and dust in galaxies linked to star formation back to roughly 13 billion years ago -- just a billion or so years after the big bang, he said.

Herschel science instruments were provided by a consortia of European institutes and with participation by NASA. NASA’s Herschel Project Office is based at JPL, which contributed technology for two of Herschel’s three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at Caltech, supports the U.S. astronomical community. Caltech manages JPL for NASA.

For more information on the Herschel Space Observatory visit http://www.esa.int/SPECIALS/Herschel/index.html orhttp://www.nasa.gov/herschel. For more information on CU-Boulder’s Center for Astrophysics and Space Astronomy visithttp://casa.colorado.edu/. For more information on CU-Boulder’s astrophysical and planetary sciences department visithttp://aps.colorado.edu/.

Jason Glenn, 303-735-5904
Jim Scott, CU media relations, 303-492-3114