Urry sheds light upon black holes

Supermassive black holes form the center of many galaxies, including our own Milky Way, but many of these bodies remained hidden until a Yale researcher went looking for them.

Ongoing research at the Yale Center for Astronomy and Astrophysics has shed light on these obscured relics of chaotic and violent galaxy creation with the aid of space-based telescopes. Center director Meg Urry said her deep-space telescope work has yielded “a census of black holes in the early universe.”

Urry led a team of astronomers analyzing space telescope data as part of the National Aeronautics and Space Administration’s Great Observatories Origins Deep Survey. The team’s results, published earlier this year, used new evidence provided by the Spitzer, Chandra X and Hubble telescopes to prove the existence of four times as many active galactic nuclei than were previously known. These nuclei are bodies often hundreds of times more massive than the sun.

The research was based upon the “unified model” of AGN, a theory Urry helped formulate in the early 1990s.

“An AGN consists of a supermassive black hole at the center, then a disc of material falling into the black hole,” Ezequiel Treister GRD ’06, a member of Urry’s team, said. “Energy from the stuff falling in is what we receive.”

Ranga Chary of the Spitzer Science Center at the California Institute of Technology, another GOODS team member, said space dust absorbs light emitted by the disc surrounding the black hole. The light is then re-released at higher wavelengths, which were previously unobservable. Researchers analyze this low frequency light to determine what fraction of it comes from AGN and what fraction comes from star formation within the same galaxy. This information allows astronomers to study the interplay between black hole formation and galaxy formation.

Since signals from all stellar objects travel at the speed of light, highly sensitive telescope images of distant galaxies afforded the team an opportunity to look back billions of years in time to what Urry said were “the teenage years of black holes.” By studying galaxies during their maturing phases, researchers can learn how the Milky Way may have evolved.

“[The research] basically tells us how we came to be here as we are,” Chary said. “By taking snapshots of the universe at different times, we are able to understand how the universe formed.”

Chary said only half of the GOODS data has been analyzed, and much more work remains to be done. In particular, scientists have yet to determine exactly what AGN evolution reveals about the development of galaxies. More study is required before definite conclusions can be made. The task of deciphering and interpreting all the data from the telescopes will require considerable time.

“We are releasing most of the data to the astronomical community, so anyone is free to work on it,” Chary said.

The completion of this GOODS project will lead to more studies, further analyzing the primitive universe, Treister said.

“We always need to go deeper,” Treister said.

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