Project B8;     (2007 - 2014)

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Gravitational Waves from Oscillations and Instabilities of Relativistic Stars

    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

Figure:
Computer simulation of the interior of an oscillating neutron star

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.

Researchers

  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

Publications

[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., Kr├╝ger, 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

Theses

[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)