N-body studies of galactic nuclei with massive black holes [Elektronische Ressource] / presented by Miguel Preto

English
190 Pages
Read an excerpt
Gain access to the library to view online
Learn more

Description

Dissertationsubmitted to theCombined Faculties for the Natural Sciences and forMathematicsof the Ruperto-Carola University of Heidelberg,Germanyfor the degree ofDoctor of Natural Sciencespresented byDiplom-Physiker Miguel Pretoborn in Lisbon, PortugalOral examination: 17 July 2007N-body studies of galactic nucleiwith massive black holesReferees: Prof. Dr. Rainer Spurzem Dr. Ralf KlesseniiAbstractMassive black holes (MBHs) are ubiquituous in galactic nuclei. The collisional dynamics ofthese dense stellar systems is studied with high resolution, direct N-body simulations andits results are thoroughly compared with those obtained from the Fokker-Planck equation,written in energy space. The predictions from the Fokker-Planck equation are validated bythe N-body results and it is concluded that the formation of a Bahcall-Wolf cusp around aMBH is a robust prediction for the old stellar populations of spheroidal systems older thanthe relaxation time as measured at the hole’s in uence radius. The mass segregation andthe scaling relations predicted for stars in di eren t mass ranges are also con r med.N-Body simulations of galaxy mergers show that binary MBHs can form with very higheccentricities after the parent galaxies settle into a newly merged nucleus. These high ec-centricities should lead to a coalescence on a very rapid time scale, as the MBHs shouldemmit strong bursts of gravitational waves at each pericenter passage.

Subjects

Informations

Published by
Published 01 January 2007
Reads 8
Language English
Document size 4 MB
Report a problem

Dissertation
submitted to the
Combined Faculties for the Natural Sciences and for
Mathematics
of the Ruperto-Carola University of Heidelberg,
Germany
for the degree of
Doctor of Natural Sciences
presented by
Diplom-Physiker Miguel Preto
born in Lisbon, Portugal
Oral examination: 17 July 2007N-body studies of galactic nuclei
with massive black holes
Referees: Prof. Dr. Rainer Spurzem Dr. Ralf Klessen
iiAbstract
Massive black holes (MBHs) are ubiquituous in galactic nuclei. The collisional dynamics of
these dense stellar systems is studied with high resolution, direct N-body simulations and
its results are thoroughly compared with those obtained from the Fokker-Planck equation,
written in energy space. The predictions from the Fokker-Planck equation are validated by
the N-body results and it is concluded that the formation of a Bahcall-Wolf cusp around a
MBH is a robust prediction for the old stellar populations of spheroidal systems older than
the relaxation time as measured at the hole’s in uence radius. The mass segregation and
the scaling relations predicted for stars in di eren t mass ranges are also con r med.
N-Body simulations of galaxy mergers show that binary MBHs can form with very high
eccentricities after the parent galaxies settle into a newly merged nucleus. These high ec-
centricities should lead to a coalescence on a very rapid time scale, as the MBHs should
emmit strong bursts of gravitational waves at each pericenter passage. The rst harmonics
of the gravitational wave strain amplitude h are estimated as the massive binary with mass
5 6 10 10 M enters the Laser Interferometer Space Antenna (LISA) frequency band.
We conclude that large-scale N-body modelling of galactic nuclei with one (several)
MBH(s) is possible with the currently available software (Sverre Aarseth’s NBODY codes
and developments therefrom) and hardware (ARI GRAPE cluster).
Zusammenfassung
Massereiche Schwarze L ocher (MSL) sind in Galaktischen Zentren allgegenwa rtig. Mit
Hilfe hochau osender, direkter N-Korper-Simulationen wird hier die sto dominierte Dy-
namik solcher dichten stellaren Systeme untersucht. Die Ergebnisse werden mit L osungen
der im Energie-Raum formulierten Fokker-Planck Gleichung verglichen. Die Vorhersagen
der Fokker-Planck Gleichung werden durch die N-Korper Ergebnisse best atigt. Es wird
gefolgert, dass fur die alte stellare Komponente sph aroidaler Systeme, die alter als die Re-
laxationszeit sind (gemessen am Ein u r adius des Schwarzen Lochs), die Entstehung eines
iii


sogenannten Bahcall-Wolf cusps um MSL eine robuste Vorhersage ist. Die fur Sterne unter-
schiedlicher Massenbereiche vorhergesagten Skalierungsbeziehungen und Massensegregation
werden ebenfalls best atigt.
N-Korper Simulationen von Galaxienverschmelzungen zeigen, dass, nachdem die beteiligten
Galaxien einen neuen gemeinsamen Kern gebildet haben, bin are MSL mit sehr hohen Exzen-
trizit aten entstehen k onnen. Hohe Exzentrizit aten sollten jedoch zur Verschmelzung der
bin aren MSL auf extrem kurzen Zeitskalen fuhren, da die MSL bei jedem Durchlauf durch
das Perizentrum erh oht Gravitationswellen abstrahlen sollten. Die ersten Harmonischen der
5Gravitationswellenamplitude h werden fur massereiche Bin arsysteme im Bereich sim10 {
610 M berechnet, die in das Frequenzband der Laser Interferometer Space Antenna (LISA)
fallen.
Wir folgern, dass die gro r aumige N-Korper Modellierung galaktischer Zentren, die ein
Schwarzes Loch (oder mehrere) enthalten, mit der z.Zt. verfugbaren Software (z.B. Sverre
Aarseth’s NBODY Codes bzw. den darauf aufbauenden Weiterentwicklungen) und Hardware
(z.B. ARI GRAPE cluster) m oglich ist.
iv




Dedication
Para a Madalena
vviAcknowledgments
First and foremost it is a great pleasure to thank my advisor Rainer Spurzem for all the
great support and enthusiasm during the last few years. His help and guidance through the
technical details of the N-body codes and his always pertinent hints to the relevant literature
were, at many times, absolutely essential. In more than one sense, it is true that without
his great generosity I would not be here writing these lines. Many thanks for everything,
Rainer!
I would also like to thank very much the other members of my PhD thesis committee:
Professors Immo Appenzeller, Ralf Klessen and Ulrich Platt.
All my colleagues at the ARI were very nice at all times. I thank all of them for their
great simpathy and very humane atittude to life in general. To all of them: Peter Berczik,
Ingo Berentzen, Andrea Borch, Jonathan Downing, Andreas Ernst, Jose Fiestas, Ovidiu
Furdui, Patrick Glaschke, Chingis Omarov, Kristina W acken, many thanks for everything.
In particular, to Jose Fiestas with whom I share the o ce, I would like to remember
here the many enjoyable conversations we had on many subjects ranging from our favorite
scienti c topics of galactic dynamics, black holes and the Fokker-Planck approximations, to
many other things of life.
I would also want to specially thank Ingo Berentzen, with whom I also had extensive dis-
cussions on Post-Newtonian dynamics, for his very sound and sober atittude of approaching
science and doing research.
I look forward to continue collaborating with you both.
I have also greatly enjoyed the wonderful atmosphere of Heidelberg, quite unique in the
world in my opinion. It was also very nice to be able to row with friends from the Heidelberger
Ruderklub, and I have enjoyed very much the Neckar valley as seen from the water.
viiviii