Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Giant Black Holes and Disks on the Balance

31.12.2002


Quasars and active galactic nuclei (AGN) are likely powered by matter accretion onto a super-massive black hole located at their center. Before being swallowed by the black hole, matter spirals towards the center, while forming an accretion disc. Unfortunately, such a disc is too small so that one can in general solve it with present day telescopes. But the technique of radio interferometry with very long base (VLBI, with base length of the size of the earth’s radius) make it possible somehow. In some objects, very intense maser emission from small molecular clouds containing water vapor and probably related to the disc have been detected. From the rotation curve of the masing disc, one can deduce some of its properties (the disc mass, its size).



Jean-Marc Huré, from the Laboratory Universe and Theories (LUTH) at Observatory of Paris-Meudon and University Paris VII, comes to show that in galaxy NGC 1068, the accretion disc would have a mass comparable with that of the black hole (with about 9 million solar masses), and a size reaching one parsec (3 light-years). Such informations bring an additional proof that the discs of quasars and AGN are indeed gigantic systems.

Quasars were discovered at the end of the Sixties. They are, with their low luminosity analogues called "Active Galactic Nuclei" (or AGN), among the most luminous objects in the Universe. Today still, all the mechanisms which could release such a power are far from being understood. However, it seems rather well established that the matter accretion on a super-massive black hole is the key-process.


The structure and the dynamics of the accretion disc remain quite mysterious. The disc is not directly observable because the resolution of current telescopes is still insufficient. It is primarily studied at short wavelengths (UV, X and gamma rays). But short wavelength spectra give information only on the internal regions of the disc (scale of the micro-parsec), very close to the black hole. The external parts of the disc (the milliparsec-scale) are made up of colder gas and radiate in the visible, infra-red, and mm bands. One suspects that at these distances, the mass of the disc (generally regarded as small) starts to play a role on its own dynamics, and thus on its evolution and its structure. At the parsec scale for example, models indicate that the mass of the disc could reach (even exceed) that of the black hole. One then expects very particular effects, like a non-keplerian rotation, and the generation of gravitational instabilities (spiral waves, etc.) who could lead to the formation of compact objects in the disc itself (like stars or planets) (Collin & Zahn, 1999, A & A, 344, 433). A point is that, the accretion disc is made of a certain amount of gas and dust, and thus it inevitably generates a certain gravity field. When this mass exceeds a fraction of the central mass (about 10% typically), then the departure to the keplerian rotation law is significant: the centrifugal force is no more compensated by the central attraction only but by the combined gravitational attraction of the black hole and of the disc.

From this point of view, an interesting case is that of active galaxy (of Seyfert-2 type) NGC 1068. One observed in this object an intense maser emission of water molecules at a distance ranging between 0.65 and 1.1 parsec of the black hole. These emissions would take place at the surface of the disc. The external rotation curve deduced from Doppler shifts does not resemble the kepler law. A recent calculation by Jean-Marc Huré, from the Observatory of Paris-Meudon and University PAris VII, (employing an inversion method of the Poisson’s equation) comes to support the assumption that the external disc could be well responsible for this non-keplerian behavior (Huré J.M., A & A Let, 2002, 395,21).

The results state indeed that one can reproduce this rotation curve provided that the outer disc has quite specific properties. Thus, parameters of the disc have been obtained. In particular, the disc would have a mass close to that of the black hole (approximately 9 million solar masses) and would be in a marginally stable state with respect to self-gravity. In addition to the constraints on the disc structure, the study also gives a value of the mass of the central black hole, inaccessible in such a galaxy by usual methods (briefly, because of a strong obscuration of this system by a torus of dust which interposes on the line of sight).

Another interesting galaxy is NGC 4258 : in this object, maser emission was also detected but here, the rotation of the disc seems in perfect agreement with Kepler’s law. Would the disc of NGC 4258 be thus not very massive, contrary to the case of NGC 1068? It is what everyone thinks... However a similar study (Huré J-M., astro-ph/0210421) shows that such a conclusion is far from being acquired. Indeed, it is possible to reproduce a keplerian rotation curve with a disc finally rather massive, reducing by 25% the mass of the black hole that one seemed to know quasi-perfectly.

The moral of the history is that the mass in the central parsec of the AGN and the Quasars is probably not concentrated into the black hole only. Other objects orbiting at these distances, to begin with the accretion disc, might contain a noticeable (even dominant) fraction of it. The inversion method used here enables to see indirectly how the mass is spatially distributed, to refine or to correct our estimations of black hole masses, and gradually to unveil the external part of the accretion discs.

Jean-Pierre Luminet | alfa
Further information:
http://luth2.obspm.fr/Compress/dec02_hure.en.html

More articles from Physics and Astronomy:

nachricht Extremely close look at electron advances frontiers in particle physics
19.10.2018 | National Science Foundation

nachricht Blue phosphorus -- mapped and measured for the first time
16.10.2018 | Helmholtz-Zentrum Berlin für Materialien und Energie

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: Goodbye, silicon? On the way to new electronic materials with metal-organic networks

Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz (Germany) together with scientists from Dresden, Leipzig, Sofia (Bulgaria) and Madrid (Spain) have now developed and characterized a novel, metal-organic material which displays electrical properties mimicking those of highly crystalline silicon. The material which can easily be fabricated at room temperature could serve as a replacement for expensive conventional inorganic materials used in optoelectronics.

Silicon, a so called semiconductor, is currently widely employed for the development of components such as solar cells, LEDs or computer chips. High purity...

Im Focus: Storage & Transport of highly volatile Gases made safer & cheaper by the use of “Kinetic Trapping"

Augsburg chemists present a new technology for compressing, storing and transporting highly volatile gases in porous frameworks/New prospects for gas-powered vehicles

Storage of highly volatile gases has always been a major technological challenge, not least for use in the automotive sector, for, for example, methane or...

Im Focus: Disrupting crystalline order to restore superfluidity

When we put water in a freezer, water molecules crystallize and form ice. This change from one phase of matter to another is called a phase transition. While this transition, and countless others that occur in nature, typically takes place at the same fixed conditions, such as the freezing point, one can ask how it can be influenced in a controlled way.

We are all familiar with such control of the freezing transition, as it is an essential ingredient in the art of making a sorbet or a slushy. To make a cold...

Im Focus: Micro energy harvesters for the Internet of Things

Fraunhofer IWS Dresden scientists print electronic layers with polymer ink

Thin organic layers provide machines and equipment with new functions. They enable, for example, tiny energy recuperators. In future, these will be installed...

Im Focus: Dynamik einzelner Proteine

Neue Messmethode erlaubt es Forschenden, die Bewegung von Molekülen lange und genau zu verfolgen

Das Zusammenspiel aus Struktur und Dynamik bestimmt die Funktion von Proteinen, den molekularen Werkzeugen der Zelle. Durch Fortschritte in der...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Conference to pave the way for new therapies

17.10.2018 | Event News

Berlin5GWeek: Private industrial networks and temporary 5G connectivity islands

16.10.2018 | Event News

5th International Conference on Cellular Materials (CellMAT), Scientific Programme online

02.10.2018 | Event News

 
Latest News

Mineral discoveries in the Galapagos Islands pose a puzzle as to their formation and origin

19.10.2018 | Earth Sciences

Less animal experiments on the horizon: Multi-organ chip awarded

19.10.2018 | Life Sciences

New method uses just a drop of blood to monitor lung cancer treatment

19.10.2018 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>