Principal Investigators: Kostas Kokkotas

*
The aim of project B8 is the study of linear and non-linear oscillations
of relativistic stars, with and without magnetic fields. The oscillations
and possible instabilities of relativistic stars can reveal a wealth of
information for their internal structure and dynamics via the emitted
gravitational waves. In this project a detailed study of the dynamics
of both old and newly born stars (uniformly or differentially rotating)
will provide the means to develop what is called gravitational wave
asteroseismology.
*

In the area of relativistic astrophysics, one of the most outstanding questions that is currently under intense investigation is the birth and evolution of compact objects. The reason is that we currently do not know the initial rotational evolution of these stars, due to the lack of relevant observations. For example, if relativistic stars rotate rapidly at birth, this would have important implications in several areas of physics. As a consequence of Einstein's theory of relativity, it is predicted that the violent pulsations excited immediately after the birth of a rotating proto-neutron star result in the emission of copious amounts of gravitational radiation.

Figure: |

In addition, Chandrasekhar, Friedman and Schutz have discovered that
certain pulsation modes grow exponentially, but only if the proto-neutron
star is rapidly rotating. The detection of gravitational waves from
pulsating neutron stars will allow the study of their interior,
in the same way as helio-seismology provides information about the
interior of the Sun. It is expected that the identification of specific
pulsation frequencies in the observational data will reveal the true
properties of matter at densities that cannot be probed today by any
other experiment. Thus, there is significant interest in this problem
also by the high-energy-physics community, since the discovery of the
true properties of matter at extremely high energies will allow
significant advances in theoretical physics and possibly new discoveries
and applications will follow. There are many issues related to compact
stars that have been explored, but there are no final answers yet.
These are:

A. how fast do neutron stars rotate at birth?

B. What are the frequencies of gravitational waves emitted by
pulsations of such stars?

C. Are there any processes through which the nearby (old) neutron
stars may emit detectable gravitational waves? And

D. what are the saturation amplitudes which can be reached by
the rotational instabilities of rotating stars?

In this project we plan to investigate and answer these types of
questions using analytic and numerical techniques.

Kostas Kokkotas | PI, PI 2007 | ||

Daniela Doneva | Postdoc, 2011 | ||

Former Associates | |||

Erich Gaertig | Postdoc, 2007-2014 | ||

Burkhard Zink | Postdoc, 2009-2013 | ||

Andrea Passamonti | Postdoc, 2010-2013 | ||

Beatrix Willburger | PhD Student, 2008 | ||

Wolfgang Kastaun | Postdoc, 2007-2010 | ||

Hajime Sotani | Postdoc, 2007-2010 | ||

Kostas Glampedakis | Postdoc, 2008-2011 | ||

Paul Lasky | Postdoc, 2009-2011 | ||

Miltos Vavoulidis | PhD Student, 2007-2008 | ||

Simos Konstantinidis | PhD Student, 2010-2011 |

[1]
*Universal I-Q relations for rapidly rotating neutron and strange stars in scalar-tensor theories*

Doneva D., Yazadjiev S., Staykov K. V., Kokkotas K.D.,
ArXiv e-prints (2014)

[2]
*Breakdown of I-Love-Q Universality in Rapidly Rotating Relativistic Stars*

Doneva D., Yazadjiev S., Stergioulas N., Kokkotas K.,
Ap. J. Letters, 781, LL6 (2014)

[3]
*Orbital and epicyclic frequencies around rapidly rotating neutron stars in scalar-tensor theories of gravity*

Doneva D., Yazadjiev S., Stergioulas N., Kokkotas, K.D., Athanasiadis, T.M.,
Phys. Rev. D, 90, 044004 (2014)

[4]
*Electromagnetic waves from neutron stars and black holes driven by polar gravitational perturbations*

Sotani, H., Kokkotas, K.D., Laguna, P., Sopuerta, C.F. (2014).,
General Relativity and Gravitation, 46, 1675 (2014)

[5]
*Non-perturbative and self-consistent models of neutron stars in R-squared gravity*

Yazadjiev S., Doneva D., Kokkotas K. D., Staykov K. V.,
Journal of Cosmology and Astroparticle Physics, 6, 003 (2014)

[6]
*Gravitational wave asteroseismology of fast rotating neutron stars with realistic equations of state*

Doneva D., Gaertig E., Kokkotas K. D., Krüger, C.,
Phys. Rev. D, 88, 044052 (2013)

[7]
*Rapidly rotating neutron stars in scalar-tensor theories of gravity*

Doneva D., Yazadjiev S., Stergioulas N., Kokkotas, K.,
Phys. Rev. D, 88, 084060 (2013)

[8]
*Evolution of the f-mode instability in neutron stars and gravitational wave detectability*

Passamonti A., Gaertig ., Kokkotas H.D., Doneva D.,
Phys. Rev. D, 87, 084010 (2013)

[9]
*Gravitationally driven electromagnetic perturbations of neutron stars and black holes*

Sotani H., Kokkotas H.D., Laguna P., Sopuerta C.F,
Phys. Rev. D, 87, 084018 (2013)

[10]
*Stability study of a model for the Klein-Gordon equation in Kerr spacetime*

H.R. Beyer, M. Alcubierre, M. Megevand, J.C. Degollado,
arXiv:1206.5187

[11]
*Nonradial oscillations of anisotropic neutron stars in the Cowling approximation*

D. D. Doneva, S.S. Yazadjiev,
Phys. Rev. D 2012, 85, 124023

[12]
*Nuclear Equation of State on r-modes instabilities in neutron stars*

Ch. C. Moustakidis,
arXiv:1205.4897v1

[13]
*Symmetry energy effects on location of the inner edge of neutron star crusts*

Ch. C. Moustakidis,
Phys. Rev. C 2012, 86, 015801

[14]
*Nonlinear viscous damping and gravitational wave detectability of the f-mode instability in neutron stars*

A. Passamonti, K. Glampedakis,
MNRAS 2012, 422, 3327

[15]
*Towards real neutron star seismology: Accounting for elasticity and superfluidity*

A. Passamonti, N. Andersson,
MNRAS 2012, 419, 638

[16]
*Possible dark energy imprints in gravitational wave spectrum of mixed neutron-dark-energy stars*

S.S. Yazadjiev, D.D. Doneva,
arXiv:1112.4375v1 (JCAP submitted)

[17]
*The f-mode instability in relativistic neutron stars*

E. Gaertig, K. Glampedakis, K., Kokkotas, K.D., Zink, B.,
Phys. Rev. Letters 2011, 107, 101102

[18]
*Gravitational wave asteroseismology with fast rotating neutron stars*

E. Gaertig, K.D. Kokkotas,
Phys. Rev. D 2011, 83, 064031

[19]
*Hydrodynamics of rapidly rotating superfluid neutron stars with mutual friction*

A. Passamonti, N. Andersson,
MNRAS 2011, 413, 47

[20]
*Solitons and Black Holes in a Generalized Skyrme Model with Dilaton-Quarkonium field*

D.D. Doneva, I.Zh. Stefanov, S.S. Yazadjiev,
Phys. Rev. D 2011, 83, 124007

[21]
*Time Evolution of the Radial Perturbations and Linear Stability of Solitons and Black Holes in a Generalized Skyrme Model*

D.D. Doneva, K.D. Kokkotas, I.Zh. Ivanov, S.S. Yazadjiev,
Phys. Rev. D 2011, 84, 084021

[22]
*Slowly rotating relativistic stars in tensor-vector-scalar theory*

H. Sotani,
Phys.Rev. D 2010, 81, 084006

[23]
*On the frequency band of the f-mode CFS instability*

B. Zink, O. Korobkin, E. Schnetter, N. Stergioulas,
Phys.Rev. D 2010, 81, 084055

[24]
*Oscillations and instabilities of fast and differentially rotating relativistic stars*

C. Krueger, E. Gaertig, K.D.Kokkotas,
Phys.Rev. D 2010, 81, 084019

[25]
*MYRIAD: A new N-body code for simulations of Star Clusters*

S. Konstantinidis, K.D. Kokkotas,
A&A in press (2010)

[26]
*Gravitational wave asteroseismology with fast rotating neutron stars*

E. Gaertig, K.D. Kokkotas,
arXiv:1005.5228

[27]
*g-modes in rotating neutron stars*

E. Gaertig, K.D. Kokkotas,
Proceedings of the 12th Marcel Grossmann, Paris, 2009

[28]
*Neutron Star Dynamics and Gravitational Waves*

K.D. Kokkotas, A. Colaiuda, E. Gaertig,
Journal of Physics: Conference Series Volume 222 012031, 2009

[29]
*Gravitational waves from neutron stars: Promises and challenges*

N. Andersson, V. Ferrari, D. I. Jones, K. D. Kokkotas, B. Krishnan, J. Read, L. Rezzolla, and B. Zink,
arXiv:0912.0384

[30]
*Oscillations and instabilities of fast rotating neutron stars*

E. Gaertig, K.D. Kokkotas,
Journal of Physics: Conference Series, 189, 012016, 2009

[31]
*Black holes and neutron stars in the generalized tensor-vector-scalar theory*

P.D. Lasky,
Phys.Rev. D 2009, 80, 081501

[32]
*Probing Tensor-Vector-Scalar Theory with Gravitational Wave Asteroseismology*

H. Sotani,
Phys.Rev. D 2009, 80, 064035

[33]
*Gravitational Radiation from Collapsing Magnetized Dust. II - Polar Parity Perturbation*

H. Sotani,
Phys.Rev. D 2009, 79, 084037

[34]
*Stellar Oscillations in Tensor-Vector-Scalar Theory*

H. Sotani,
Phys.Rev. D 2009, 79, 064033

[35]
*Relativistic g-modes in rapidly rotating neutron stars*

E. Gaertig, K. D. Kokkotas,
Phys. Rev D 2009, 80, 064026

[36]
*Alfvén Polar Oscillations of Relativistic Stars*

H. Sotani, K. D. Kokkotas,
MNRAS 2009, 395, 1163

[37]
*On the oscillations of dissipative superfluid neutron stars*

N. Andersson, K. Glampedakis, B. Haskell,
Phys. Rev. D 2009, 79, 103009

[38]
*Superfluid signatures in magnetar seismology*

N. Andersson, K. Glampedakis, L. Samuelsson,
MNRAS 2009, 396, 894

[39]
*On the Quasi-Periodic Oscillations of Magnetars*

A. Colaiuda, H. Beyer, K. D. Kokkotas,
MNRAS 2009, 296, 1441

[40]
*Structure of neutron stars in tensor-vector-scalar theory*

P.D. Lasky, H. Sotani, D. Giannios,
Phys. Rev. D 2008, 78, 104019

[41]
*Gravitational Wave Astronomy*

K.D. Kokkotas,
Reviews in Modern Astrophysics, Vol 20, p. 140 "Cosmic Matter", WILEY-VCH, Edi.S. Röser (2008)

[42]
*Oscillations of rapidly rotating relativistic stars*

E. Gaertig, K.D. Kokkotas,
Phys. Rev. D 2008, 78, 064063

[43]
*Pressure gradients, shell crossing singularities and acoustic oscillations - application to inhomogeneous cosmological models*

Krzysztof Bolejko, Paul Lasky,
MNRAS 2008, 391, L59

[44]
*Inertial modes of rigidly rotating neutron stars in Cowling approximation*

Wolfgang Kastaun,
Phys. Rev. D 2008, 77, 124019

[45]
*Non-axisymmetric oscillations of differentially rotating relativistic stars*

A. Passamonti, A. Stavridis, K. D. Kokkotas,
Phys. Rev. D 2008, 77, 024029

[46]
*Crustal Oscillations of Slowly Rotating Relativistic Stars*

M. Vavoulidis, K.D. Kokkotas and A. Stavridis,
MNRAS 2008, 384, 1711

[47]
*Gravitational Waves*

K.D. Kokkotas,
ACTA PHYSICA POLONICA B, Volume:38, Issue:12, pages 3891-3923, 2007

[48]
*Constraints on the Magnetic Field Geometry of Magnetars*

H. Sotani, A. Colaiuda, K. D. Kokkotas,
MNRAS 2008, 385, 2161

[49]
*Alfven QPOs in Magnetars*

H. Sotani, K.D. Kokkotas and N. Stergioulas,
MNRAS 2008, 385, L5

[50]
*Torsional Oscillations of Slowly Rotating Relativistic Stars*

M. Vavoulidis, A. Stavridis, K.D. Kokkotas and H. Beyer,
MNRAS 2007, 377, 1553

[51]
*Non-radial Oscillations of Slowly and Differentially Rotating Compact Stars*

A. Stavridis, A. Passamonti and K.D. Kokkotas,
Phys. Rev. D 2007, 75, 064019

[52]
*Study of the gravitational wave emission from stellar systems*

S. Konstantinidis,
Phd Thesis, Aristotle University of Thessaloniki (2011)

[53]
*Simulating the gravitational field of a non-rotating neutron star on GPUs*

G. Tantilian,
Master Thesis, Aristotle University of Thessaloniki (2011)

[54]
*Linear Oscillations of Compact Stars in the Cowling Approximation*

E. Gärtig,
PhD thesis, University of Tübingen (2008)

[55]
*The Structure of Magnetized Axisymmetric Equilibria*

M. Bölling,
Diploma thesis, University of Tübingen (2008)

[56]
*Black-Hole Oscillations : Astrophysics and Thermodynamics*

I. Gerritsen,
Diploma thesis, University of Tübingen (2008)

[57]
*Gravitational Collapse of a Magnetized Star*

N. Oppermann,
Diploma thesis, University of Tübingen (2009)

[58]
*Differentially Rotating Neutron Stars in the Cowling Approximation*

C. Krüger,
Diploma thesis, University of Tübingen (2009)

[59]
*Rotating Relativistic Stars*

M. Vavoulidis,
PhD thesis, University of Thessaloniki (2008)