Subscribe free to our newsletters via your
. 24/7 Space News .




TIME AND SPACE
Galaxy mergers not the trigger for most black hole feeding frenzies
by Tim Stephens
Santa Cruz CA (SPX) Oct 18, 2011


A survey of distant galaxies found that disk galaxies like those pictured above are just as likely to host active galactic nuclei as galaxies involved in disruptive mergers, like those in the images below. Credit: A. Koekemoer (Space Telescope Science Institute), NASA, ESA.

A survey of distant galaxies using the Hubble Space Telescope has put another nail in the coffin of the theory that galaxy mergers are the main trigger for turning quiescent supermassive black holes into radiation-blasting active galactic nuclei.

Led by astronomers at the University of California, Santa Cruz, the new study examined the morphology and structure of distant galaxies hosting active central black holes. The researchers found that these galaxies were no more likely to be involved in an ongoing merger than non-active galaxies of similar mass.

"Theoretical models show that a merger is a great way to trigger an active galactic nucleus, because it funnels a lot of gas to the center of the galaxy. But we found that most of the host galaxies did not look disturbed.

They look like disk galaxies, and a disk would be destroyed by a merger," said Dale Kocevski, a postdoctoral researcher at UC Santa Cruz and first author of a paper on the findings to be published in the Astrophysical Journal.

A supermassive black hole (millions or even billions of times the mass of the sun) sits at the core of most if not all large galaxies. But only a fraction of these are the bright radiation sources known as active galactic nuclei, which light up when the central black hole is actively gobbling up nearby gas clouds.

The galactic center glows brightly at all wavelengths because the gas heats up as it falls into the black hole and emits intense radiation.

"The problem has been how to get the gas into the center of the galaxy, rather than orbiting around in the disk," said coauthor Sandra Faber, University Professor of astronomy and astrophysics at UC Santa Cruz.

The study used new images from Hubble's WFC3 infrared camera taken as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). Faber, who leads the CANDELS project, said the images include galaxies at distances of nearly 11 billion light years. Looking deep into space gives astronomers a window back in time, revealing earlier stages in the evolution of the universe.

This study covered a period when the brightest active galaxies, known as quasars, were at their peak, and theoretical models predicted that galaxy collisions would be an important trigger, Faber said. "Theory says that collisions should be more important, but we did not find that," she said.

These are not the first findings to suggest that violent galactic mergers are not needed to fuel active black holes. Earlier imaging studies of galaxies at distances of up to 8 billion light years had also failed to find evidence that mergers were triggering most active galactic nuclei.

More recently a team of astronomers reached the same conclusions based on an analysis of the distribution of active galaxies out to almost 11 billion light years. But only Hubble's WFC3 could provide images showing the morphologies of galaxies at that distance.

"We were surprised to see that they look a lot like galaxies much closer to us," Faber said.

If galaxy collisions are not responsible for triggering active galactic nuclei, it suggests less violent processes within galaxies may play a greater role in feeding black holes, Kocevski said. "We call these secular processes. They happen randomly about ten percent of the time and are common in the local universe, such as when a star or a giant gas cloud gets too close and falls into the black hole."

Alternatively, the black holes may be fueled by a process that is unique to the early universe. "Recent theories suggest distant galaxies are fed by streams of cold gas, which can lead to violent instabilities in disk galaxies that result in large amounts of gas being funneled to the central black hole," Kocevski said. "Only with further study will we know for sure."

Kocevski and Faber worked with an international team of scientists from 21 institutions on the study, which was supported by NASA through a grant from the Space Telescope Science Institute (STScI). The paper's 38 coauthors are affiliated with UCSC, STScI, Max Planck Institute for Extraterrestrial Physics, Imperial College of Science, Johns Hopkins University, University of Michigan, Durham University, Laboratoire AIM Paris-Saclay, University of Nottingham, Hebrew University, University of Edinburgh, University of Maryland, National Observatory of Athens, University of Massachusetts, Carnegie Institution of Washington, University of Arizona, National Optical Astronomy Observatories, University of Missouri, UC Riverside, Institut de Ciencies del Cosmos, and NASA Goddard Space Flight Center.

About CANDELS

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) is a powerful imaging survey of the distant universe being carried out with the Hubble Space Telescope. It is the largest project in the history of Hubble, with 902 assigned orbits of observing time. CANDELS makes use of the near-infrared WFC3 camera and the visible-light ACS camera. Together, these two cameras give unprecedented panchromatic coverage of galaxies from optical wavelengths to the near-infrared. The power to look deeper into space and further back in time will enable CANDELS to construct a "cosmic movie" of galaxy evolution that follows the life histories of galaxies from infancy to the present time. This work will cap Hubble's revolutionary series of discoveries on cosmic evolution and bequeath a legacy of precious data to future generations of astronomers. CANDELS will also test the reality of cosmic dark energy by measuring the brightness of type Ia supernovae.

.


Related Links
Space Telescope Science Institute
Understanding Time and Space






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TIME AND SPACE
Astrophysicists Find Evidence of Black Holes' Destruction of Stars
New York NY (SPX) Oct 12, 2011
Astrophysicists have found evidence of black holes destroying stars, a long-sought phenomenon that provides a new window into general relativity. The research, reported in the latest issue of the Astrophysical Journal, also opens up a method to search for the possible existence of a large population of presently undetectable "intermediate mass" black holes which are hypothesized to be precursors ... read more


TIME AND SPACE
Subtly Shaded Map of Moon Reveals Titanium Treasure Troves

NASA's Moon Twins Going Their Own Way

Titanium treasure found on Moon

NASA Invites Students to Name Moon-Bound Spacecraft

TIME AND SPACE
New Mystery on Mars's Forgotten Plains

Russian scientists want to join Europe's ExoMars mission

UK Space Agency announces seed funding for Mars exploration

While the US Stalls, Europe Moves On to Mars

TIME AND SPACE
Astrotech Subsidiary Awarded Task Order for NASA Mission

ASU in space: 7 current missions, more in the wings

Branson opens world's first 'spaceport' in New Mexico

Branson opens Virgin Galactic Gateway to Space at Spaceport America

TIME AND SPACE
China's first space lab module in good condition

Takeoff For Tiangong

Snafu as China space launch set to US patriotic song

Civilians given chance to reach for the stars

TIME AND SPACE
Ultrasound 2: Taking Space Imaging to the Next Level

CU-Boulder to play key role in global student space experiment competition

It's All in the Mix With Fluid Physics in Space

DLR ROKVISS robotic arm returns from space

TIME AND SPACE
Soyuz is put through its paces for Thursday's launch

Russia blames scientists for rocket crashes

Space Exploration Technologies Ready to Compete for Upcoming DoD Launches

Huge stakes riding on maiden Soyuz launch from Kourou

TIME AND SPACE
UChicago launches search for distant worlds

UChicago launches search for distant worlds

Astronomers Find Elusive Planets in Decade-Old Hubble Data

University of Texas-led Team Discovers Unusual Multi-Planet System with NASA's Kepler Spacecraft

TIME AND SPACE
RIM out to rev up BlackBerry with new apps

RIM rallies developers to burnish BlackBerry

IBM stock sags on revenue target miss

Samsung seeks iPhone sales ban in Japan, Australia




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement