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Black holes : observations Lecture 7: Horizon and exotics

Black holes : observations Lecture 7: Horizon and exotics. Sergei Popov ( SAI MSU ). Plan of the lecture. Primordial BHs. Limits. Emission of evaporating BHs . The horizon problem . Black holes and fundamental theories . Alternatives to BHs . Constraints. Main reviews and articles

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Black holes : observations Lecture 7: Horizon and exotics

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  1. Black holes: observationsLecture 7: Horizon and exotics Sergei Popov (SAI MSU)

  2. Plan of the lecture • Primordial BHs. Limits. • Emission of evaporating BHs. • The horizon problem. • Black holes and fundamental theories. • Alternatives to BHs. Constraints. • Main reviews and articles • astro-ph/0504034Primordial Black Holes - Recent Developments • astro-ph/0304478 Gamma Rays from Primordial Black Holes • in Supersymmetric Scenarios • gr-qc/0304042 Do black holes radiate? • gr-qc/0506078 Black Holes in Astrophysics • astro-ph/0207270 No observational proof of the black-hole event-horizon • gr-qc/0507101 Black holes and fundamental physics • astro-ph/0401549Constraining Alternate Models of Black Holes: Type I X-ray Bursts on Accreting Fermion-Fermion and Boson-Fermion Stars

  3. Primordial black holes Primordial black holes(PBH)are formed with masses about the massinside a horizon at the given moment (particle horizon). Hawking radiation BHs with M>1026 g have temperatures lower than the CMB radiation. The time for complete evaporation

  4. EGRET and constraints onPBH Background radiation at energies: 30 MeV – 120 GeV. The upper limit on the density of PBHs

  5. Constraints on cosmological parameters from data on PBH Data on PBHs in principle can provide constraints on different cosmologicalparameters related to the density fluctuations. For example, on the parametern, characterising the power spectrum of fluctuations. About other constraints seeCarr (2005) astro-ph/0504034

  6. Particle emission during PBH evaporation When a BH mass is below 1014g,it starts to emit hadrons.

  7. Particle spectrum for uniform distribution of PBHs

  8. PBHand antiprotons Antiprotons are detected in cosmic rays. They are secondary particles. Properties of these secondaryantiprotons should be different fromproperties of antiprotons generatedduring PBH evaporation at energies0.1-1 GeV. Comparison between calculationsand the observed spectrum ofantiprotons provides a limit onthe spatial density of PBHs. (Barrau et al. 2003, taken fromCarr 2005)

  9. Spectra in different models The spectrum can be non-thermal.This is due to creation of particleswhich then demonstrate series oftransformations (decays) and interactions; only at the very end we have photons. And their spectrum is different from the thermal(i.e. from the blackbody). However, the situation is not that clear(see recent criticizm in arXiv: 0709.2380). (arXiv: 0706.3778)

  10. The horizon problem • What can be a 100% proof that we observe a BH? • Of course, only a direct evidence for the horizon existence! • But it is very difficult to prove it! • One can try to follow three routes: • To look for direct evidence for the horizon. • To try to prove the absence of a surface. • To falsify the alternative models. • The first approach is not very realistic (astro-ph/0207270 Abramowicz et al.) Only in future we can hope to have direct images from the horizon vicinity(for example, forSgr A* the corresponding size is 0.02 milliarcseconds), or to have data from BH coalescence via GW detection. (seeNarayan gr-qc/0506078)

  11. Dreams about direct images Prototype: 100 microarcsecs MAXIM: 100 nanoarcsecs 33 satelliteswith X-ray opticsand a detector in 500 km away. (Narayan 2005) TheMAXIM Project (Cash 2002) http://beyondeinstein.nasa.gov/press/images/maxim/

  12. Absence of surface Here we mostly discuss close binaries with accretion • Lack of pulsations • No burster-like bursts • Nowhere to collect matter. • (however, see below about some alternatives) • Low accretion efficiency (also forSgr A*) • ADAF. Energy is taken under horizon. • No boundary layer (Sunyaev, Revnivtsev 2000) • Analysis of power spectra. • Cut-off in BH candidates above 50 Hz.

  13. Parameters of different models Fermion stars: Mf=223 MeV (non-interacting) Mmax=12.61 M0 R(M=10M0)= 252 km= 8.6 Rsh Collapse after adding 0.782 M0of gas. Bozon stars: Mb=2.4 10-17MeV, λ=100 Mmax=12.57 M0 R(M=10M0)= 153 km (99.9% of mass) Collapse after adding 0.863 M0of gas. Model parameters are constrainedby limits on the maximum sizeof an object derived from QPOsat 450 Hz (astro-ph/0401459)

  14. Stability respect to flares on a surface Rmin=9/8 Rsh Potentially, smaller radii are possible,but such objects should beunstable in GR. Still, if they are possible, then one can “hide” bursts due tohigh redshift. (astro-ph/0401459)

  15. Timing characteristics of surface bursts (astro-ph/0401459)

  16. Stability respect to flares inside an object Fermion stars Bozon stars (astro-ph/0401459)

  17. Timing characteristics of internal bursts (astro-ph/0401459)

  18. BHs and fundamental theories • Thermodynamics of BHs and Hawking radiation. • Testing alternative theories of gravity. • Black holes and extra dimensions • Accelerator experiments Under some reasonable assumptionsastrophysical data can providestrong and important constraintson parameters of fundamental theories.

  19. Brane worlds and black holes In astro-ph/0612611 the authors discussconstraints on parameters of world on branebasing on observations of XTE J1118+408. The idea is the following. In many scenariosof brane world BHs lifetimes are short.An estimated of a lower limit on the ageof a BH can provide a stronger limitthan laboratory experiments. (see alsoastro-ph/0401466)

  20. BH spin and testing the GR (astro-ph/0402213)

  21. QPO in GRO 1655-40 If the interpretation of QPOs inthis source is correct, than we can “look inside” 3Rg. The observed frequency is 450 Hz.Uncertainties (dashed lines) aredue to uncertainty in the mass: 5.8-7.9 solar masses. However, this conclusion cruciallydepends on our understanding ofthe QPO phenomenon. Here it is assumed that fQPO<fAZIM=(GM)1/2/2πR3/2 (astro-ph/0402213)

  22. Alternatives • Gravastar - GRAvitational VAcuum STAR (Mazur, Mottola gr-qc/0109035) • Dark energy stars (Chaplin astro-ph/0503200) • Boson stars (see, for example, Colpi et al. 1986 Phys. Rev. Lett.) • Fermion balls (see discussion in Yuan et al. astro-ph/0401549) • Evaporation before horizon formation(Vachaspati et al. gr-qc/0609024 ) Except general theoretical criticizm, some models are closed by absence of burster-like flares (Yuan et al. astro-ph/0401549). This is not the case for models like those proposed by Vachaspati et al. However, they are activley critisized by theorists. Taking all together, black hole – is the most conservative hypothesis!

  23. GRAvitational VAcuum STAR Vacuum outside, Vacuum inside Do not produce Hawking radiation. Can be distinguished in coalescence. Schwarzschild De Sitter (Mazur, Mottola gr-qc/0109035)

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