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CHALLENGES OF RELATIVISTIC ASTROPHYSICS Reuven Opher (Univ. of Sao Paulo/Cornell. Univ.)

CHALLENGES OF RELATIVISTIC ASTROPHYSICS

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Reuven Opher ( Univ. of Sao Paulo/Cornell. Univ.) . CHALLENGES OF RELATIVISTIC ASTROPHYSICS . WHAT ARE THE BIGGEST PROBLEMS THAT NEED TO BE SOLVED IN RELATIVISTIC ASTROPHYSICS? IF YOU WERE ASKED TO NAME SIX, WHAT WOULD THEY BE?. HERE ARE MINE!. SUBJECTS. Dark Energy (2) Dark Matter - PowerPoint PPT Presentation

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Page 1: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGES OF RELATIVISTIC ASTROPHYSICS

Reuven Opher(Univ. of Sao Paulo/Cornell. Univ.)

Page 2: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

WHAT ARE THE BIGGEST PROBLEMS THAT NEED TO BE SOLVED IN RELATIVISTIC ASTROPHYSICS?

IF YOU WERE ASKED TO NAME SIX, WHAT WOULD THEY BE?

Page 3: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

HERE ARE MINE!

Page 4: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

SUBJECTS(1) Dark Energy(2) Dark Matter(3) Highest Energy Cosmic Rays(4) Primordial Universe(5) New Physics at > 2 x Nuclear Density (6) Gamma Ray Bursts

Page 5: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (1): WHAT IS CAUSING THE RECENT ACCELERATION OF THE UNIVERSE?

Gravity always decelerates, so this so-called “Dark Energy” that solves the acceleration problem, acts like “Anti-Gravity”.WHAT IS IT?

Page 6: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (2a): WHERE ARE THE PREDICTED ABUNDANT SMALL DARK

MATTER HALOS ?

The standard theory predicts that there are thousands of small massive non-baryonic “Dark Matter” halos in the Milky Way.

WHERE ARE THEY?

Page 7: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (2b): WHERE ARE THE PREDICTED SMALL DARK MATTER HALOS WITH CUSPS?

The standard theory predicts that in the small non-baryonic “Dark Matter” halos there are cusps.(In a cusp the density goes to infinity as the radius goes to zero.)WHERE ARE THESE CUSPS?

Page 8: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (3): WHAT IS THE MOST POWERFUL COSMIC ACCELERATOR?

It accelerates particles to energies ten million times higher than the most powerful accelerator on Earth.

WHAT IS IT?

Page 9: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (4): WHAT IS THE SELF-CONSISTENT THEORY OF PRIMORDIAL INFLATION?

There is considerable observational evidence indicating that a primordial inflation period occurred.BUT: (1) AT WHAT ENERGY?(2) WHAT NEW PHYSICS IS INVOLVED? (3) IS IT SUFFICIENTLY CLOSE TO THE PLANCK ENERGY THAT QUANTUM GRAVITY EFFECTS ARE IMPORTANT?(4) ARE THE POTENTIALS USED UNREASONABLE?

Page 10: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (5): WHAT IS THE BEST WAY TO DETECT THE NEW PHYSICS

At > 2 x NUCLEAR DENSITY IN NEUTRON STARS?

Page 11: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (6): WHAT IS THE ENERGY SOURCE OF GAMMA RAY BURSTS (GRBs)?

When a GRB explodes it is brighter than the whole universe.It emits in one second what the Sun emits in its lifetime.WHAT IS ITS ENERGY SOURCE?

Page 12: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

(1) DARK ENERGY

Page 13: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (1): WHAT IS CAUSING THE RECENT ACCELERATION OF THE

UNIVERSE?

Page 14: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

IS VACUUM ENERGY THE SOURCE?

All existing data is consistent with the Dark Energy being a small vacuum energy density.

The main problem is that theory predicts that the vacuum energy density is 120 orders of magnitude bigger than what is observed.

Page 15: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ALTERNATE THEORIES INSTEAD OF VACUUM ENERGY

Cosmic Axion Tracker FieldExponential Potential SpintessenceK-Essence Ghost CondensateThawing Model Freezing ModelPhantom Energy f(R) TheoriesScalar-Tensor Theory Palatini FormalismBrane World Gravity Modified Gravity(R.R. Caldwell and M. Kamionkowski, Ann. Rev. Nucl. Sci. 59, 397 (2009))(J.A. Frieman, M.S. Turner and D. Huterer, Ann. Rev. Astron. Astrophys. 46, 385 (2008))

Because of the large number of theories, we all agree that no final answer has been found.

Page 16: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

MY BEST CANDIDATES FOR DARK ENERGY

(1) THERE IS A PHYSICAL REASON WHY THE VACUUM ENERGY IS SMALL.

(2) DARK ENERGY IS A MANIFESTATION OF THE GROWTH OF INHOMOGENEITY IN THE UNIVERSE.

Page 17: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

WHAT IS NEEDED

At a given redshift, due to Dark Energy, objects are more distant, older and contains more volume.

We need, then, many more precise observations as a function of redshift of:(1) STANDARD CANDLES (e.g., Supernovae Ia),

(2) STANDARD RULERS(e.g. Baryon Acoustic Oscillations),

(3) STANDARD DENSITIES (e.g. Clusters of galaxies, galaxies and Dark Matter Halos)(observed with gravitational lensing)).

Page 18: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

(2) DARK MATTER

Page 19: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (2a): WHERE ARE THE PREDICTED ABUNDANT SMALL DARK MATTER HALOS ?

The standard theory predicts that there are thousands of small massive non-baryonic “Dark Matter” halos in the Milky Way.

WHERE ARE THEY?

Page 20: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

DARK MATTER HALOS WITHOUT STARS

Primordial Magnetic Fields strongly influence the baryon gas fraction of a Dark Matter halo and can prevent small Dark Matter halos to have visible stars. (R. De Souza, L.F. Rodrigues and R. Opher, MNRAS 410, 2199 (2011))

Page 21: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (2b): WHERE ARE THE PREDICTED SMALL DARK MATTER

HALOS WITH CUSPS? The standard theory predicts that there are thousands of small non-baryonic “Dark Matter” halos with cusp central densities in the Milky Way.WHERE ARE THE CUSPS?

Page 22: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

DARK MATTER HALOS WITHOUT PREDICTED CENTRAL CUSPS

A single supernova explosion in a small Dark Matter halo can transform a cusp into a core (a finite density at the center). (R. De Souza, L.F. Rodrigues, E. Ishida and R. Opher, MNRAS 415, 2969 (2011))

(The supernova expels the baryonic matter which perturbs the gravitational potential sufficiently to transform the cusp into a core.)

Page 23: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

WHAT IS NEEDED

(1) Gravitational lensing detection of small Dark Matter Halos that have no stars, to see if they exist.

(2) Observing stellar orbits in small galaxies with Dark Matter halos to determine the gravitational potential and the central Dark Matter halo density, to see if it is a cusp or not.

Page 24: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (3): WHAT IS THE MOST POWERFUL COSMIC

ACCELERATOR?

Page 25: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

THE HIGHEST ENERGY COSMIC RAYS

The highest energy cosmic rays have energies 1020 eV, ten million times more energetic than the most energetic particles accelerated on earth (e.g., in the LHC in CERN, Switzerland).

WHAT IS THE ACCELERATOR?

Page 26: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

GENERALLY ACCEPTED THEORY OF THE ACCELERATION OF COSMIC RAYS IN SHOCKS

It is generally accepted that the acceleration of high energy cosmic rays, until at least 1015 eV, isFirst Order Fermi acceleration in a supernova shock.

In this process, particles bounce back and forth between the downstream turbulence and the upstream Alfven waves that were produced by a streaming instability of the accelerated particles.

Assuming that the shock velocity is higher than the Alfven velocity, the particles gain energy each time they bounce off the Alfven waves streaming into the shock.

Page 27: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CONDITIONS FOR ACCELERATION

The limit ~ 1015 eV is due to the radius of curvature of the accelerated particle ( proton) not being greater than the size of the supernova remnant in the ambient magnetic field ~ 5-10 microgauss.

We can only reach ~ 1020 eV if : a) the Magnetic Field is amplified; and/or b) the acceleration region is bigger; and/or c) the accelerated particle is an iron nucleus and not a proton.

Page 28: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ACCELERATION IN THE BIG POWERFULACTIVE GALACTIC NUCLEI (AGN)

SHOCKS

The highest energy cosmic rays, ~ 1020 eV, need to come from a distance < 75 Mpc.

The few AGNs < 75 Mpc are not strongly correlated with the high energy cosmic rays 1020 eV.(K-H. Kampert et al., arXiv: 1207.4823)

Page 29: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CREATION OF LARGE MAGNETIC FIELDS

A very large random Magnetic Field, much greater than the ambient Magnetic Field ( 5-10 microgauss), can be generated by the cosmic ray streaming instability in the precursor of supernova shocks.(A.R. Bell, MNRAS 353, 550 (2004))THUS THE ACCELERATED PARTICLES NOT ONLY PRODUCE ALFVEN WAVES BUT ALSO CREATE LARGE MAGNETIC FIELDS.

Page 30: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ACCELERATION IN SUPERNOVA SHOCKS WHERE THE MAGNETIC FIELD HAS BEEN AMPLIFIED

The Magnetic Fields in young supernovae remnants are observed to be amplified to 150-500 microgauss.(H.J. Volk, E.G. Berezhko and L.T. Ksenfontov, A&A 433, 229 (2005)Younger supernovae remnants have stronger fields.

Page 31: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ACCELERATION OF IRON NUCLEI IN SUPERNOVA SHOCKS WHERE THE MAGNETIC FIELD HAS BEEN AMPLIFIED

Iron nuclei can be accelerated to ~ 1019 eV in these amplified Magnetic Fields in supernova remnants.(V. Ptuskin, V. Zirakashvili and E-S. Seo, Ap. J. 718, 31 (2010)) A factor of ten, however, is missing to reach 1020 eV.

Page 32: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ELIMINATING THE SHOCK IN FIRST ORDER FERMI ACCELERATION

The First-Order Fermi accelerated particles can slow down the incoming matter into the shock, eliminating the shock entirely, and the source might be observed as just a smooth adiabatic compression. (G. Medina-Tanco and R. Opher, Astron. Ap. 240, 178 (1990)THESE COMPRESSIONS COULD BE AROUND GALAXIES AND CLUSTERS OF GALAXIES, WITH NO SHOCK BEING OBSERVED.

Page 33: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

WHAT IS NEEDED

More data on the highest energy cosmic rays to

localize and identify the sources and their nature

(protons or iron nuclei).

Page 34: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (4): WHAT IS THE SELF-CONSISTENT THEORY OF PRIMORDIAL INFLATION?

Page 35: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

EVOLUTION OF THE UNIVERSE

Page 36: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

VARIOUS SUCCESSES OF ASSUMING A PRIMORDIAL INFLATION ERA

(1) Non-causally connected regions today were causally connected in the past;(2) The universe has little curvature today (Kinetic Energy ~ Potential Energy);(3) The density perturbation spectrum is almost scale invarient ( independent of scale, they have the same amplitude when they enter the horizon); (4) Relics of gauge symmetry breaking are not observed(e.g. monopoles);(5) Almost Gaussian perturbations ( one part in a thousand); and(6) Perturbation modes began with the same phase (could have been random).

BUT……

Page 37: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ENERGY SCALE OF INFLATION

The energy scale of inflation is predicted to be on the order of 1016 GeV, VERY MUCH HIGHER THAN THE ENERGIES OF THE STANDARD MODEL OF PARTICLE PHYSICS ~ 104 GeV.

FROM 104 GeV to 1016 GeV there could easily be new physics.

Page 38: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

THE POPULAR CHAOTIC INFLATION MODEL

The popular chaotic inflation model of a massive scalar field F with a mass m and a potential equal to m2F2/2, the mass needs to be m ~ 4 x 1012GeV to satisfy observations.

FOR AN EXPECTED INFLATION PERIOD ~ 1016GeV, THE MASS IS EXTREMELY SMALL AND UNNATURAL.

Page 39: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

AMPLITUDE OF DENSITY FLUCTUATIONS

In the standard model of Inflation, the amplitude of the density fluctuations at the Inflation Era is 3H3/V’, where H is the Hubble radius in the Inflation Era and V’ is the derivitive of the Inflation potential with respect to the field.

THE THEORY DOES NOT GIVE THE VALUE OF V’TO OBTAIN THE OBSERVED DENSITY FLUCTUATION ( ~ 10-5).

Page 40: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

FLATNESS OF INFLATION POTENTIAL

The present popular model of inflation requires a very flat slow-roll potential to obtain the observed density fluctuations, in which the potential, V ~ (1016 GeV)4, changes negligibly with a change in the field, DF ~ Mpl ~ 1019 GeV or V/(DF)4 < 10-12 .

NO KNOWN PARTICLE HAS SUCH A FLAT POTENTIAL.

Page 41: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

INFLATION FROM QUANTUM GRAVITY

Non-commutation of space and time and Lorentz Invariance Violation , indicated by quantum-gravity, can produce inflation. (U. Machado and R. Opher, Class. Quant. Grav. 29, 065003, (2012))(U. Machado and R. Opher, arXiv:1211.6478)

Page 42: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

WHAT IS NEEDED(1) Detailed observations of Tensor Fluctuations.

(2) Detailed observations of Gaussianity Fluctuations .

(3) Investigation of Lorentz Invariance Violation.

The Tensor Fluctuations give information on the energy and the fields and potentials of the inflation era.

The Gaussinaity can give information on, for example, the possible existence of Cosmic Strings, predicted by String Theory.

Page 43: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

WHAT IS NEEDED

Lorentz Invariance Violation can be investigated by measuring the velocity of high energy photons.

(A deviation from the velocity of light as a function of E/Epl might be expected, where E is the energy of the photon and Epl is the Planck energy.)

Page 44: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (5): WHAT IS THE NEW PHYSICS At > 2 x NUCLEAR DENSITY IN NEUTRON STARS?

Page 45: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

NEW PHYSICS AT THE CENTER OF NEUTRON STARS

Most models of dense matter predict that at the density > 2 times nuclear density in Neutron Stars, the formation of exotic matter takes place ( e.g., free quarks).(J.M. Lattimir and M. Prakash, Phys. Rep. 442, 109 (2007))

Page 46: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

SUPERFLUIDITY IN NEUTRON STARS

The cooling Neutron Star, in the Cassiopeia A supernova remnant, gives evidence for superfluidity in the core.(P.S. Shternin et al., arXiv:1012.0045)

Page 47: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

DETECTING THE NEW PHYSICS IN NEUTRON STARS

Tidal Polarizability, dependent on the new physics at the center of Neutron Stars, is measureable in the Gravitational Wave signal of merging Neutron Star binaries.(T. Damour et. Al., arXiv:1203.4352E.E. Flanagan and T. Hinderer, Phys. Rev. D77, 021502 (2008)J.E. Vines and E.E. Flanagan, arXiv:1009.4919,C. Messenger and J. Read, arXiv:1107.5725)

Page 48: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

WHAT IS NEEDED(1) GRAVITATIONAL WAVE DETECTIONAdvanced LIGO is expected to detect ~ 40 ( with an uncertainty of 0.4-400) binary neutron star merger events per year and could detect the Tidal Polarizability.( J. Abadie et. al., Class. Quant. Grav. 27, 17001 (2010))

(2) DETECTION OF M vs R OF NEUTRON STARS.

Page 49: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CHALLENGE (6): WHAT IS THE ENERGY SOURCE OF GAMMA RAY BURSTS (GRBs)?

Page 50: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ARTIST VISION OF A GRB AND ITS RELATIVISTIC JETS

Page 51: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

OBSERVING RELATIVISTIC JETS OF GRBs

Evidence of the Relativistic Jets of GRBs is the observed achromatic break from radio to X-rays. (Predicted to occur when the Lorentz factor becomes equal to one over the opening angle).(S.B. Cenko et al., Ap. J. 711, 641 (2010))

Page 52: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ENERGY SOURCE: A SPINNING BLACK HOLE IN A MAGNETIC FIELD?

A Relativistic Jet is produced with a maximum power:P ~ 1051 B2 M2 ergs/swhere B is in units of 1015G and M is in solar mass units.(J.C.M. McKinney, A. Tchekhovsky and R. D. Blandford, MNRAS 423, 3083 (2012))(R.D. Blandford and R.L. Znajek, MNRAS 179, 433 (1977))

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ENERGY SOURCE: A SPINNING BLACK HOLE IN A MAGNETIC FIELD?

The 1015G could come from the collapse of a Neutron Star (Magnetar) with a field > 1013G.

The 1015G could also come from a spinning Neutron Star which amplifies its Magnetic Field by the dynamo effect during collapse.

Page 54: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

ENERGY SOURCE: A SPINNING BLACK HOLE IN A MAGNETIC FIELD?

FOR M SEVERAL SOLAR MASSES AND B ~ 1015G, THE POWER OBTAINED IS COMPARABLE TO THAT OF GRBs.

THE SPINNING BLACK HOLE IN THE MAGNETIC FIELD COULD COME FROM THE COLLAPSE OF A MASSIVE STAR.

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WHAT IS NEEDED

MORE DETAILED SPECTROSCOPIC DATA OF GRBs AT SHORT TIMES.

Page 56: CHALLENGES OF RELATIVISTIC ASTROPHYSICS

CONCLUSION

WE MIGHT NOT ANSWER THESE CHALLENGES IN THE NEXT TEN YEARS,

BUT

WE CERTAINLY WILL ENJOY OURSELVES TRYING!!