Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Galaxy mergers not the major feeding mechanism for giant black holes

05.01.2011
A new study has obtained unexpected new insight into the feeding habits of the giant black holes, which are responsible for the emissions of some of the brightest objects in the universe: active galactic nuclei.

Previous models had often assumed that mergers between galaxies are instrumental in driving matter into these black holes. But this systematic study of 1400 galaxies – the largest sample ever examined for the purpose – presents strong evidence that, at least for the past eight billion years, black holes have acquired their food more peacefully. The study will be published in the Astrophysical Journal on January 10.


If major mergers are an important factor in transporting matter towards galaxies\' central black holes, which makes the black hole shine out brightly as an Active Galactic Nucleus (AGN), then distortions - the tell-tale traces of such mergers - should be more frequent for active galaxies (left) than inactive ones (right). Credit: NASA/ESA and M. Cisternas (MPIA)

The emissions of active galactic nuclei (AGN) are driven by matter falling into the galaxy's supermassive central black hole. But it is an open question in the physics of active galaxies how matter traverses the final hundreds of light-years to reach the immediate neighborhood of the black hole and be swallowed.

Following a study by David Sanders and collaborators from the late 1980s, most astronomers thought they had the answer: Mergers between galaxies of similar sizes ("major mergers") would dramatically disturb the galaxies' gas, and make some of it fall towards the central black hole.

While this is a plausible scenario, only a systematic study can show whether or not this is indeed how giant black holes acquire their food. This is what Mauricio Cisternas and Knud Jahnke from the Max Planck Institute for Astronomy (MPIA) set out to do in 2008. Cisternas explains: "A study of this scope has become possible only recently, with the large surveys undertaken using the HUBBLE Space Telescope. Before, there was simply no way to examine sufficiently many active galaxies at large cosmic distances in sufficient detail."

Cisternas and his collaborators obtained data for 140 active galactic nuclei (AGN), identified as such by X-ray observations from the XMM-Newton space telescope as part of the multi-wavelength survey COSMOS. Light from the most distant of these AGN has been traveling for almost 8 billion years to reach us (redshift z=1): We see those AGN as they were 8 billion years ago, and the sample probes most of the black hole growth during the second half of cosmic history.

What makes this study special is the systematic way the astronomers selected a "control group" of ordinary galaxies without an active black hole – in other words, which do not have a black hole swallowing copious amounts of matter. For each of the AGNs in the study, nine non-active galaxies at roughly the same redshift, and thus roughly in the same stage of cosmic evolution, were selected from the same HUBBLE images, for a grand total of 1400 galaxies. This selection procedure allowed for a direct comparison between AGN and a matching population of ordinary, inactive galaxies.

The tell-tale sign that a galaxy has undergone a major merger over the past few hundred millions of years are distortions of its shape. For galaxies this distant, on images of the given resolution, a computerized, automatic identification of the degree of distortion cannot currently compete with visual inspection of the images by astronomers. Co-author Knud Jahnke (MPIA) says: "We were faced with the problem of bias. We knew that mergers were a plausible driver of AGN activity, so would we be more likely to classify AGN as distorted because of what we expected to find?"

In order to eliminate possible bias, the researchers set up a blind study – standard operating procedure in fields like medicine or psychology, but unusual in astronomy. Cisternas removed tell-tale signs of galactic activity from the images so there would be no way to directly distinguish between the images of active and inactive galaxies.

The images were then given to ten galaxy experts based at eight different institutions, who were asked to judge each galaxy as "distorted" or "not distorted". While their individual judgements showed significant variation, there was unanimity on the crucial question: None of the classifications showed a significant difference between AGN and inactive galaxies. There was no significant correlation between a galaxy's activity and its distortion, between its black hole being well-fed and its involvement in a major merger.

While mergers are a common phenomenon, and are thought to play a role at least for some AGN, the study shows that they provide neither a universal nor a dominant mechanism for feeding black holes. By the study's statistics, at least 75%, and possibly all of AGN activity over the last 8 billion years must have a different explanation. Possible ways of transporting matter towards a central black hole include instabilities of structures like a spiral galaxy's bar, the collisions of giant molecular clouds within the galaxy, or the fly-by of another galaxy that does not lead to a merger ("galactic harrassment").

Could there still be a causal connection between mergers and activity in the more distant past? That is the next question the group is gearing up to address. Suitable data is bound to come from two ongoing observational programs ("Multi-Cycle Treasury Programs") with the HUBBLE Space Telescope, as well as from observations by its successor, the James Webb Space Telescope, which is scheduled for launch after 2014.

Contact

Mauricio Cisternas (lead author)
Max Planck Institute for Astronomy
Phone: +49 6221 528-335
E-Mail: cisternas@mpia.de
Dr. Knud Jahnke (second author)
Max Planck Institute for Astronomy
Phone +49 6221 528-398
E-Mail: jahnke@mpia.de
Dr. Markus Pössel (public relations)
Max Planck Institute for Astronomy
Phone: (+49|0) 6221 – 528 261
E-mail: pr@mpia.de
Background information
The work described here will be published as Cisternas et al., "The bulk of black hole growth since z~1 occurs in a secular universe: no major merger-AGN connection" in December 10, 2010 issue of the Astrophysical Journal (volume 726, p. 57ff.). The team members are Mauricio Cisternas, Knud Jahnke, Katherine J. Inskip (all Max Planck Institute for Astronomy), Jeyhan Kartaltepe (NOAO), Anton M. Koekemoer (STScI), Thorsten Lisker (Heidelberg University), Aday R. Robaina (MPIA and University of Barcelona), Marco Scodeggio (IASF-INAF), Kartik Sheth (California Institute of Technology), Jonathan R. Trump (University of Arizona), Rene Andrae (MPIA), Takamitsu Miyaji (UNAM, Mexico, and University of California at San Diego), Elisabeta Lusso (INAF - Astronomical Observatory of BOLOGNA), Marcella Brusa (Max Planck Institute for Extraterrestrial Physics), Peter Capak (Caltech), Nico Cappelluti (MPE), Francesca Civano (Harvard Smithsonian Center for Astrophysics), Olivier Ilbert (Laboratoire d’Astrophysique de Marseille), Chris D. Impey (University of Arizona), Alexie Leauthaud (LBNL and University of California), Simon J. Lilly (ETH Zürich), Mara Salvato (Max Planck Institute for Plasma Physics), Nick Z. Scoville (Caltech), and Yoshi Taniguchi (Ehime University, Japan).

Dr. Markus Pössel | Max-Planck-Institut
Further information:
http://www.mpia.de

More articles from Physics and Astronomy:

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

nachricht What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>