Major questions in astrophysics and particle physics

P Darriulat, Ha Noi, October 2008

SCALES IN THE

UNIVERSE

Mass (solar masses)vs. size (cm)80 orders of magnitude in

ordinate60 orders in magnitude in

abscissa

HEISENBERGLIMIT

Pion (M=140MeV, R=1fm)

Parton (q, g)m, r << M. R

MR~ ħ

Gravity energy in wave packet of size L and mass M

is ~ GM2/LMust be less than ΔE = ħ/L

Hence M < √(ħ/G)This is the Planck mass

MPlanck ~ 1019 GeV

rr

∞

V=√ (2MG/r)

V=0

M

SCHWARZSCHILDLIMIT

Schwarzschild metric

ds2=dt2–dl2

V=√ (2MG/r) γ = 1/√(1–V2)=1/√(1–MG/r)

ds2=(γdt)2–(dl/γ)2

Hence a singularity at

r=2MG=3 km/MSun

ħ=c=G=1Heisenberg limit MR=1

Schwarzschild limit R/M=2Planck scale essentially at the

intersection, R=M=1that is 10-33cm and 1019GeV

Beyond this limit gravity and quantum physics are incompatible

Need new physicsSuperstrings

STARS AND GALAXIES

Spectacular progress over past decades in understanding how stars are born, how

they live on the main sequence and how they die

(white dwarfs, neutron stars, black holes)

Main problems are a) Formation of galaxiesand galactic black holes

b) UHE cosmic rays

c) Dark matter

The birth of starsLeft: NGC604 in Triangulum, 2.7Mly away (HST) one of the

largest SFR known to us in a nearby spiral. Right: a SFR in the Milky Way, (Trapezium in Orion nebula).

NS

WDMS

Chandrasekhar

BH

Sun

The death of stars

HN

SN II

SN Ia

Not to scale!

SN1987a and the Crab nebula SN1054

MS Star White dwarf Neutron star

R(km) 106 104 10 -102

D(kg/m3) 103 109 1015-1018

T(s) 106 102 10-4-10−2

H(T) 1 104 108-1010

Conservation of mass, angular momentum and magnetic flux

Object R0 (km) M/M☼ RSch

Earth 6.4 10–6 9 mm

Sun 7 105 1 3 km

Sgr A* BH 3.106 107 km

Cyg X1 SBH 10 30 km

Cyg A GBH 5.109 1.5 1010 km

Nucl. Matt*. 9 3 9 km

* Remember M☼ ~1057 GeV

Stellar black holes

Many stellar black holes (mostly members of binaries) are known today.

The most massive is in M33, 16 solar masses, 1 Mpc away and orbits its companion (70 solar

masses!) in 3.5 days. Discovery released in October 2007.

The least massive is 3.8 solar masses, 3 kpc away, discovery released in January 2008.

Intermediate mass black holes are also known, such as one of 4±1 104 solar masses at

the centre of the globular cluster ω Cen.

Cyg X1, the most famous stellar black holeOne of the most intense X-ray sources in the sky, 8.7

solar masses, 2 kpc away, orbits its companion variable blue supergiant in 5.6 days, discovered in 1964 (rocket flight), then Uhuru (Giacconi et al.),

extensively studied, sometimes called microquasar

X-ray (HERO) Artist impression

GRB 080319B, visible by naked eye, 7.5 Gly awayCollapse of a very massive star into a black hole.

Many galactic black holes have been studied, two of them in many details:

Sgr A*, in the centre of our galaxy,

10 kpc away from us,3 million solar masses

Cen A, in the centre of a nearby galaxy,

10 Mpc away from us,200 million solar masses

Cyg A

Sagittarius A* was first seen as an intense radio source

Zooming in more at 6 cm wave length

The highest resolution VLA image, 2ly×2ly

At visible wave lengths nothing to be seen but dustAlready in the near infrared one starts to see the

galactic centre glowing.

Zooming in

Stars are observed in infrared as orbiting around a 3million solar masses black hole

2-8 keV Chandra and Naos Conica VLT mid infrared. Sgr A* <1.4 arcsec in diameter, consistent with

accretion disc of a 3 million solar masses black hole.

A particularly striking occurrence of three strong flares within a bit more than a day.

Twenty times as many active X ray binaries as expected, suggesting that ten thousand stellar black holes may be orbiting Sgr A*

including enhanced population of stellar black holes. It is compact, flary,

jetty and the accretion disk is surrounded by a ring of dust

(1 to 2 pc radius) fed by dense clouds 10 to 20 pc

away and three arms of hot gas (>10000K) spiralling

toward SgrA*

Sgr A*: a short summaryOverwhelming evidence in favour of a black hole, 3 million solar masses as measured from Keplerian movement of stars

around it, anchored at the centre of the Galaxy, in a very dense environment (1 million times larger than that of the Sun)

Cen A is one of the brightest radio sources in the sky

Centaurus A (NGC1528) contains the closest AGN, 33 Mpc away from us,

X-rays (Chandra) reveal two jets

The Black hole has a mass of 100 to 200

million solar masses

Visible: an elliptical (white glow) having collided with a spiral

(revealed by the dark dust band across it )

In the visible, the elliptical is obscured by dust, infrared reveals the spiral.

Star forming regions are present.

Ripples are remnant of a gigantic explosion some ten million years ago

High resolution composite image of the Cen A jet

Composite images showing all Cen A main features

Cen A: a short summary

Overwhelming evidence in favour of a black hole:

It is compact, massive, jetty and the accretion disk is

surrounded by a circumnuclear ring, all features consistent with

what can be expected for a 200 million solar masses

black hole (measured from Keplerian flow of gas

around it).

Formation of galaxiesand galactic black holes

Increasing evidence that early galaxies (Universe less than 1 Gy old) were small and often colliding/merging

in the then much denser Universe. Many questions still unanswered.

Less massive galactic black holes conceivably formed by merging of stellar black holes in the dense

environment of galaxy centres. But more massive galactic black holes more difficult to understand.

Again possible important role of early galaxy collisions and merging.

The Antennae galaxy, 20 or so Mpc away from us

Left: ground

telescope. Right:

zooming with HST

Details reveal intense star formation activity

Other documented examples, including collisions of >2 galaxies

HST, IR

Other examples of multiple collisions

The Cartwheel Galaxy, a collision between two galaxies

Abell 754 is made of the merging of two

small clusters

NGC1700, 30 kpc in diameter, intense X-ray

source (Chandra)likely to result from a collision between an elliptical and a spiral

M82 may have collided with M81 and produce NGC3077. It has an AGN in its centre

Central region (HST) Subaru

Chandra UV radio

M94 (UV) centre of NGC4314

Spectacular rings of stars are visible near the centres of

active galaxies

Image of the galaxy cluster Abell 400 (blue=X, pink=radio)

showing jets from two merging AGNs.

Cosmic rays

Evidence for acceleration around the shock of young SNRs for galactic

cosmic rays.Extragalactic cosmic ray astronomy

taking off (Auger)suggesting AGNs as sources

(probably again diffusive shock acceleration).

Shell SNRs and plerions, studied in great detail by X-ray (synchrotron and inverse Compton) and γ-ray (π0

decays) astronomy are seen to accelerate galactic cosmic rays near the shell (shock wave)

Cassiopeia A (Chandra) Crab Nebula (Chandra)

X ray images allow for very high resolutions

KeplerSNR 1604

TychoSNR 1572

N 49

Den

sity

Radius

Forward shock

Reverse shock Cas A Tycho’s

Bd = 10 μG

Bd = 500 μG

Direct evidence for

magnetic field

amplification

RX J1713: Chandra observes variable shock structure, suggestive of substantial magnetic field amplification

Colliding galaxies and merging galaxy clusters are sites of large scale shocks

Abell 3667

X-ray surface brightness

Turbulent gas flow

XMM temperature map (U.G. Briel et al)

Radio emission: Remnant of large scale (>1 Mpc) particle acceleration site

Auger: The first four-fold eventMay 2007, ~1019 eV

Circles of 3.1o on 27 UHECR detected by Auger Red crosses are 472 AGN (318 in field of view)

having z<0.018 (D<75Mpc) Solid line shows field of view (zenith angle < 60o)

Color tells exposureDashed line is super galactic plane

DARK MATTER

Main evidences are from stellar rotation curves (v=cte instead of v=1/√r) and from binding energy of clusters of galaxies. Also from gravitational lensing and stability of spirals. Must be cold (to allow galaxies to form). The most popular candidate today is the LSP (lightest SUSY partner). ΩCDM=22±3%

MORE ON DARK MATTER The galaxy cluster Abell 2029 contains thousands of galaxies (optical image, right) enveloped in a gigantic cloud of hot gas (X-ray image, left), and an amount of dark matter equivalent to more than a hundred trillion Suns. At the center of this cluster is an enormous, elliptically shaped galaxy that is thought to have been formed from the mergers of many smaller galaxies. X-rays are produced by the multimillion degree gas which is confined to the cluster primarily by the gravity of dark matter.

Their temperature and intensity distributions

allow for mapping that of dark matter in the inner

region of the galaxy cluster. Results are consistent with the

predictions of cold dark matter models.

GLOBAL (MIS)UNDERSTANDING

OF THE DYNAMICS OF THE UNIVERSE

Direct measurement of the present rate of expansion

(Hubble constant)+

Red shift and inhomogeneities of CMB

+ Hypothesis of homogeneity at

large scales

PREDICTA 4 times denser Universe than we know of: DARK ENERGY

HUBBLE EXPANSION

From Cepheids

to SN Ia

H=71±3km/s/Mpc

But large redshift galaxies are too

faint:

q=-d2a/adt2/H2

=-.66±.10 → w=p/ρ= -1.0±0.2

Cosmic Microwave Background

At an age of ~ 400 kyr (z~1000) the universe had a temperature in the eV region: electrons and nuclei combined into atoms. It then became transparent to the left over photons that can still be observed today, redshifted by a factor of ~1000.

This tells us about the state of the universe at that time and about its evolution thereafter.

A perfect black body spectrum

• Evidence for thermal equilibrium

• T=2.725(1)K

tells us about redshift

between now and then

Angular aperture of inhomogeneities can’t be larger than ratio of horizons between then and now (400ky/14Gy) multiplied by redshift (1000)

Δθ<~1o

CMB INHOMOGENEITIES

From COBE to WMAP

FOURIER ANALYSIS (spherical harmonics)

Below some threshold in l the

amplitudes of the Ylm

terms should therefore cancel.

The position of the first peak (l~220) tells us about Ω:

Ω=1.02±0.02

the universe is flat

WMAP SUMMARY (March 2006)

Name Symbol (unit) Value error + error –

Hubble constant H(km/s/Mpc) 70.9 2.4 3.2

Baryon fraction ΩB (%) 4.44 0.42 0.35

Matter fraction ΩB+CDM (%) 26.6 2.5 4.0

Critical density ρcrit (10–26kg/m3) 0.94 0.06 0.09

Dark energy ΩΛ (%) 73.2 4.0 2.5

Redshift reionization zion 10.5 2.6 2.9

Age of Universe T(Gy) 13.73 0.13 0.17

Equation of state w – 0.926 0.051 0.075

Spatial curvature k – 0.010 0.014 0.012

NUCLEOSYNTHESISDepending on the expansion

rate when the density and temperature of the Universe corresponded to significant

nuclear physics cross sections (MeV scale) one can predict deuterium and helium

abundances. As 8Be is unstable, there was not

enough time to form 12C, the next even-even nucleus. Comparing to measured

abundances gives ΩM=4.4%, of which a third or so is

made of stars and the rest of hot gases in galaxy clusters.

Global outcome

Putting all these data together we get a consistent picture of a flat universe,

13.7±0.2Gyr old, and having the following energy content:

4% of nuclei (~1% in stars and ~3% in hot gas), 23% of dark matter and the remaining 73%, called dark energy, are a complete mystery

ENERGY CONTENT OF THE UNIVERSE

Concordance for an accelerating

expansion and an equation of state of dark energy having

w= -1, hence corresponding to a

cosmological constantDark Energy 73%

CDM 23%

Baryons 4% + < 1%

DARK ENERGY

w q n

Matter dominated 0 1/2 2/3

Radiation dominated 1/3 1 1/2

Inflation; dark energy −1 −1 ∞

Accepting the CMB result that the Universe

is flat, 73% of the energy density is unexplained:

dark energy. Agrees with fainter distant galaxies

(q= 0.67± 0.25) Concordance with the

predictions of a cosmological constant

(Λ-CDM model) w= –0.93± 0.06

EINSTEIN-STRAUSS’s SWISS CHEESEAND WALLS & VOIDS STRUCTURE

A local static Schwarzschild metric can be reconciled with

an expanding Friedmann-Robertson-Walker metric in a Swiss cheese picture. But what about walls and voids? There the argument does not

apply.

ρe

M

2Rb

Schwarzschild

FRW

Some people claim that this may be mimicking dark energy.

Schematic evolution of the universe

PARTICLESSpace-time symmetry

+Exchange symmetries

+Gauge invariance

→Standard model of massless

particles+

Higgs mechanism and symmetry breaking

→Standard model of massive

particles

Scale: LHC scale (sub TeV)

Standard model of massless particles : space-time symmetry

• Poincaré group of Lorentz transformations:

- translations (energy-momentum is a 4-vector),

- space rotations (spin)

- Lorentz boosts (space-time rotations, left and right representations, Dirac spinors, antiparticle-particle relation)

- Supersymmetry (relating fermions to bosons)• Particles defined by covariant spin and mass • The Standard Model starts by assuming the existence of a

single spin ½ fermion species, f • Particle-sparticle doublets (R-parity)

Standard model of massless particles : exchange symmetry

• The single fermion species (out of some 1080 fermions in the universe!) may exist in different forms, specified by indices: fi,j,k…

• Group symmetries define the exchange from one index to another: Ui1,i2

• SU(3)×SU(2)×U(1) describes colour×weak-isospin×charge (hypercharge) exchanges associated with strong, weak and electromagnetic forces respectively

• Quark-lepton symmetry and three families are not understood. Unification is believed to take place at GUT scale, >~1016 GeV, close to the Planck scale (1019GeV)

Major questions: three families, lepton-quark symmetryQuarks: (u,d) (c,s) (t,b)

Leptons: (e, νe) (μ, νμ) (τ, ντ)

Standard model of massless particles : gauge invariance

• Gauge invariance (local) requires that we may choose the phases of the fields as we like at any point of space-time and ascertain that the exchanged states still satisfy Dirac equation. It is not possible.

• The way out is to introduce massless gauge vector bosons that compensate exactly for the effect. We need as many as there are generators in the exchange group. They couple directly to the fermion field

• U(1) gives the photon; SU(2) gives three weak bosons, W+, W- and Z; SU(3) gives 8 gluons.In fact the photon and weak bosons mix with weak (Weinberg) angle θW , sin2 θW = 0.23

Standard model of massive particles : spontaneous symmetry breaking,

Higgs mechanism• The favoured way to generate masses uses the fact

that SU(2)×U(1) symmetry breaking relates to non-zero masses (mass terms are of the form fLfR)

• Introducing a pair of complex scalar fields with a locus of degenerate minima generates 3 Goldstone bosons that give masses to the weak bosons and a 4th scalar: the Higgs boson

• More complex schemes are possible with several Higgs bosons, but the mechanism remains the same

• However no Higgs boson has yet been observed, the current mass limit is 114 GeV.

Current limit on Higgs mass (from LEP)

Standard model of massive particles : Supersymmetry

The Higgs mechanism generates weak boson masses commensurate with the only available scale,

MPlanck=1019 GeV, rather than 100 or so GeV as required.The favoured way to prevent this to happen is to introduce

supersymmetry (SUSY), a symmetry between bosons and fermions.

While fermions are prevented to acquire large masses by SU(2)×U(1) symmetry, SUSY will do it for bosons.

SUSY is in fact a fundamental symmetry of space-time. Its commutators are proportional to momentum and gauging it

generates gravity (SUGRA)However, no SUSY partner of any known particle has yet

been observed. They are expected in the 100 to 1000 GeV range.

PLANCK SCALE

At or near the Planck scale is the place where

superstrings are attempting to answer nearly all of our

unanswered questions.Close to it (less than three orders of magnitude) are

the Grand unification scaleand the domain of inflation

which is ruling the evolution of the very early

Universe

InflationThere are serious hints in favor of a “grand unification”

of the electroweak and strong forces at a mass MGUT

~a few 1016 GeV, close to the Planck mass (1019 GeV)

What happened at that time brings up a number of problems: flatness, causality, monopoles, ρa4 . All of these are elegantly solved by assuming an exponential expansion (constant H) during these very early times (t<10-33 s) due to a metastable state having energy density ~MGUT

4

However we know of no realistic detailed model of such an inflation mechanism

The major questionsAt the largest scale (horizon) What is “dark energy” hiding?

Near or at Planck scale:Unification of gravity with quantum physics

Inflation, the early UniverseThree flavours, lepton-quark symmetry, grand unification

Near or at LHC scaleMass generation, where is (are) the Higgs(es)?

Is the world supersymmetric?What is dark matter made of?

With LHC taking off three of the seven major questions which we were able to identify are likely

to receive an answer in the few years to come.

After nearly twenty years of preparation the LHC community will now harvest the fruits of their hard

work.

Thanks to them we all shall live exciting times.

Best wishes to them for big successes with the expected and good surprises with the unexpected!

It is great time for students to join the particle physics community!

Good luck to all of you!

Thank you for your attention!