testing general relativity - ulisboa · 2015-12-19 · p. pani - testing general relativity @ gr...
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Testing General Relativitywith present and future astrophysical observations
Paolo PaniSapienza University of Rome & Instituto Superior Técnico, Lisbon
Berti+, Topical Review Class.Quant.Grav. 32 (2015) 24, 243001;
Gair+, Living Rev. Relativity 16 (2013), 7;
Yunes & Siemens, Living Rev. Relativity 16 (2013), 9
GR 100 Years in Lisbon, IST 18-19 December 2015
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P. Pani - Testing General Relativity @ GR 100 Years in Lisbon 2
Outline
Testing gravity: why bother?
– A compass to navigate the modified-gravity atlas
– Approaches and tests
Astrophysical tests of gravity
– GW emission, propagation, polarization
– Tests of compact objects, black-hole paradigm
– Probing Dark Matter with strong gravity
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Why testing gravity?
Strong-field regime unexplored
Dark energy
Dark matter
Quantum gravity Singularities
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Was Einstein right?“Why do you spend so much time testing GR? We know that the theory is right.”
– S. Chandrasekhar to his postdoc Clifford Will
Will, Living Reviews (2014)
Local Lorentz invarianceWeak equivalence principle
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Is Einstein still right?
QED~1920s 10-9 meters
10-15 metersQCD
~1950s
Mechanics~1700ish 10-3 meters
Classical tests of GR~1920s10-7
0.1-1 Compact objects~2010s-2020s
Newton~1700ish
10-11
Lengthscale Grav. Potential[G M/(c^2 r)]
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Is Einstein still right?
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How could Einstein be wrong?
Auxilary fields
Eddington-inspired Born-Infeld
[adapted from Clifton, Ferreira, Padilla, Skordis, Phys. Rep. 2011]
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How could Einstein be wrong?Berti+, Topical Review in CQG (2015) [1501.07274]
Lovelock's theorem:
[Sotiriou, Lect.Notes Phys. 892 (2015) 3-24]
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How could Einstein be wrong?Berti+, Topical Review in CQG (2015) [1501.07274]
Lovelock's theorem:
[Sotiriou, Lect.Notes Phys. 892 (2015) 3-24]
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Properties of (some) modified theoriesBerti+, Topical Review in Class.Quant.Grav. 32 (2015) 24, 243001]
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Part IIAstrophysical tests of GR
Image credit: Tanja Bode of Georgia Tech
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Probes of strong-field gravity
Gravitational waves– Emission
– Propagation
– Polarization
Black holes– No-hair theorems
– Stability
Neutron stars– Degeneracy with EoS
Exotic objects
GW detectors
(aLIGO, aVIRGO, KAGRA,…, eLISA)
Radio telescopes
(Timing, PTAs, SKA)
VLBI, VLTI, NIR
(Event Horizon Telescope, GRAVITY,...)
Satellites
(NICER, LOFT,...)
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Tests of GW polarizations/speed
Metric theory → 6 polarizations
“Multipolarity” & energy loss
– Monopole, dipole, quadrupole,….
Propagation
– Graviton dispersion relation
– eLISA projected bound on the graviton mass:
– GW phase VS EM phase
– Parity violations (amplitude birefringence)
[Will, Living Review Relativity 2006-2014]
[Gair+, Living Review Relativity 2012]
[Will 1997, Berti 2004]
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Tests of the BH no-hair theorem
Emission from accreting BHs (continuum fitting, K-alpha line)
Quasiperiodic oscillations (QPOs)
Ringdown
BH shadows
EMRIs/IMRIs
[Bambi+, 2011-2015]
[Maselli+, 2015]
[Berti, Cardoso, Starinets, 2009]
[Cunha+ 2015, Johanssen+, 2015]
[Ryan, 1999]
In my entire scientific life [...] the most shattering experience has been the realization that an exact solution of Einstein's equations of general relativity, discovered by [...] Roy Kerr, provides the absolutely exact representation of untold numbers of massive black holes that populate the universe.
S. Chandrasekhar
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BH solutions beyond GRBerti+, Topical Review in Class.Quant.Grav. 32 (2015) 24, 243001]
Same metric does NOT mean same dynamics!
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QNM Zoo & Ringdown tests
EDGB gravity
Boson stars
…
Parametrized Ringdown Approach
– Lack of theory
– Excitation?
[Barausse, Cardoso, Pani; 2014]
Chern-Simons Gravastar
dRGT massive gravity
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NS solutions beyond GRBerti+, Topical Review in Class.Quant.Grav. 32 (2015) 24, 243001]
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Part IIIChallenging GR
A biased overview
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Spontaneous scalarization
In static stars In NS-NS binaries
In BHs with matter
[Damour & Esposito-Farese, Phys.Rev.Lett. 70 (1993) 2220-2223]
[Barausse, Palenzuela, Lehner, Phys.Rev. D87 (2013) 081506]
[Cardoso, Carucci, Pani, Sotiriou, Phys.Rev.Lett. 111 (2013) 111101]
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Floating orbits in ST gravity
Generic effect → only needs light boson coupled to matter
Floating orbit at Ωp ~ μ
S
[Cardoso, Chakrabarti, Pani, Berti, Gualteri+, Phys.Rev.Lett. 107 (2011) 241101]
Narrow resonances → fragile?
Energy flux balance:
Excitation of the scalar QNMs → resonances
Superradiant energy extraction[Brito, Cardoso, Pani, “Superradiance” (2015)]
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Bounds on Lorentz violations
[Yagi, Blas, Yunes, Barausse, Phys.Rev.Lett. 112 (2014) 16, 161101]
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Instabilities in massive gravity
[de Rham, Gabadadze, Tolley, Phys.Rev.Lett. 106 (2011) 231101]
(Bidiagonal) Schwarzschild BHs are Gregory-Laflamme unstable! [Babichev & Fabbri, Class.Quant.Grav. 30 (2013) 152001][Brito, Cardoso, Pani; Phys.Rev. D87 (2013) 12, 124024]
Nonbidiagonal BHs are stable[Babichev & Fabbri, Phys.Rev. D89 (2014) 081502]
[Babichev, Brito, Pani; arXiv:1512.04058]
(Bidiagonal) Kerr BHs are superradiantly unstable [Brito, Cardoso, Pani; Phys.Rev. D87 (2013) 12, 124024]
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Singularity avoidance
Singularity-avoidance inside BHs
Pani, Cardoso, Delsate, PRL 2011
Pani & Sotiriou, PRL 2012
Modified mass-radius diagram for white dwarfs
Pani, Delsate, Cardoso, PRD 2011
Banados & Ferreira, PRL 2010
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Testing the BH paradigm
[Macedo, Pani, Cardoso, Crispino, Astrophys.J. 774 (2013) 48]
BH mimickers unstable?
Ergoregion instability
Fragmentation?
Light-ring → horizonCardoso+, Phys.Rev. D90 (2014) 044069
Friedman, Commun.Math.Phys.,63,243 1978
EMRIs around boson stars[Kesden, Gair, Kamionkowski; Phys.Rev. D71 (2005) 044015]
QNMexcitation
No horizonHigher frequency
[Pani+, Phys.Rev. D81 (2010) 084011 ]
[Macedo+, Phys.Rev. D88 (2013) 6, 064046]
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Probing DM with strong gravity
Observations of highly-spinning BHs → bounds on ultralight particles
[R. Brito, V. Cardoso, P. Pani; “Superradiance” - Springer (2015)]
[BH mass]
[BH
angula
r m
om
entu
m]
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GR, live long and prosper
After a century, General Relativity keeps surprising us
Recent conceptual, observational and technical breakthroughs
Entering a new exciting area of astrophysics@extreme gravity
“Black holes teach us that [...] the laws of physics that we regard as ‘sacred,’ as immutable, are anything but.”
J.A. Wheeler
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This work is supported by the European Community through
the Marie Curie IEF contracts aStronGR-2011-298297 and
AstroGRAphy-2013-623439, and by FCT - Portugal through
projects IF/00293/2013.
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Backup slides“Nothing is More Necessary
than the Unnecessary”
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Which approach to test gravity?
Null experiments Direct approach
- Inefficient
- Need strong motivation
+ More precise
Smoking guns
- Inefficient
+ Large corrections
+ New effects
Parametrizations
+ Efficient
- Small corrections
- Sufficiently general?
- Reference quantities?
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Probing DM with binary pulsars
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Part IVCan environmental effects spoil
precision GW astrophysics?
Barausse, Cardoso, Pani; Phys.Rev. D89 (2014) 10, 104059
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Env. corrections to GW dephasing
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Env. corrections to BH ringdown
QNMs are NOT ringdown modes!
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[Credit: Ana
Sousa]