CR Suomijarvi chap1 6

Slide1: 

Hanoi, August 2005 Observations of Cosmic Rays Lecture 1: Origin of Cosmic Rays Tiina Suomijärvi Institut de Physique Nucléaire Université Paris XI-Orsay, IN2P3/CNRS France

Why to study cosmic rays ?: 

Why to study cosmic rays ? Cosmic rays span over an enormous range of energies, up to 1020 eV They are abundant and serve an important role in the energy balance of galaxy. Their energy density 1 eVcm-3 is comparable to that contained in the galactic magnetic field or in the cosmic microwave background. They are evidence of powerful astrophysical accelerators (supernovae, active galactic nuclei…) and can be used to study these accelerators

Why to study cosmic rays…: 

Why to study cosmic rays… They propagate through universe and can give information on properties of cosmic environment (magnetic fields, matter densities…) Their chemical composition, modulated by propagation, reflects the nucleosynthetic processes occurring at their origin and can also be used to measure age of astrophysical objects (cosmic ray clocks: 10Be t1/2 = 1.5 106y) They can be used to study the validity of physical laws in extreme conditions (violation of Lorentz invariance?) They can be messengers of « new physics » or yet unknown particles Composition (at ~GeV): 85% H (p) 12% He (a) 1% heavier nuclei 2% e± (³90% e- ) 10-5-10-4 antiprotons.

Dimensions and time scale: 

Dimensions and time scale Formation of galaxies Electroweak transition The unit of distance in astronomy is called the parallax-second, or parsec. It is defined to be the distance at which the mean radius of the Earth’s orbit about the sun subtends an angle of one second of arc. 1 pc = 3.08 1016 m = 3.26 light years

The large scale distribution of matter and radiation in the Universe: 

The large scale distribution of matter and radiation in the Universe Measurements of the cosmic microwave background (CMB): evidence for the overall isotropy of the Universe Discovered by Penzias and Wilson 1965 CMB is the cooled remnant of the early phase of the Universe

CMB from COBE measurements: 

CMB from COBE measurements The plane of the Milky Way Galaxy is horizontal across the middle of each picture. Sagittarius is in the center of the map,Orion is to the right, and Cygnus is to the left. The map including the dipole and Galaxy on the top, the dipole removed map in the middle, and the reduced map on the bottom. The dipole, is due to the motion of the solar system relative to distant matter in the universe. The blue and red spots correspond to regions of greater or lesser density in the early Universe. These "fossilized" relics record the distribution of matter and energy in the early Universe before the matter became organized into stars and galaxies. Spectrum of the CMB: COBE (Cosmic Background Explorer, launched in 1989) CMB spectrum: black body radiation with T=2.7 K corresponding to an energy density of 2.62 105 eV m-3

Distribution of visible matter: 

Distribution of visible matter Sky distribution of approximately 30000 galaxies from CfA Catalog. Plot is made in galactic coordinates. The distribution of galaxies is highly irregular, with huge holes, filaments and clusters occurring in the local Universe The Wilkinson Microwave Anisotropy Probe (WMAP) team has made the first detailed full-sky map of the oldest light in the universe. The most striking features about the CMB is its uniformity. Only with very sensitive instruments can detect fluctuations. By studying these fluctuations, one can learn about the origin of galaxies and large scale structures and measure the basic parameters of the Big Bang theory.

The Virgo cluster: 

The Virgo cluster The Virgo Cluster with its some 2000 member galaxies dominates our intergalactic neighborhood. It represents the physical center of our Local Supercluster and influences all the galaxies and galaxy groups by the gravitational attraction of its enormous mass. The center of the Virgo cluster is about 15-20 Mpc from our galaxy. The Virgo Cluster of Galaxies, and is centered on the giant elliptical galaxy M87. The two bright galaxies on the right (west) are (right-to-left) M84 and M86; starting from these two, a chain of galaxies ("Markarian's chain") stretches well to the upper (northern) middle of our image (and beyond, well to M88 which is slightly outside above the sky area photographed our image).

Hubble law: 

Hubble law Hubble 1929: the Universe of galaxies is in a state of uniform expansion. All galaxies are receding from our galaxy, the further away a galaxy is from us, the greater its velocity of recession v: v=H0r, r is the distance of the galaxy H0 is the Hubble constant ) The current value of the Hubble constant is still debated, values near the high and low ends of 50 and 100 km s-1/Mpc.

The galaxies: 

The galaxies Galaxies are the basic building blocks of the Universe. Basic distinction is between spiral and elliptical galaxies. Spiral galaxy: The Milky Way is the galaxy which is the home of our Solar System together with at least 200 billion other stars (more recent estimates have given numbers around 400 billion) and their planets, and thousands of clusters and nebulae Elliptical galaxy: The giant elliptical galaxy M87, also called Virgo A, is one of the most remarkable objects in the sky. It is perhaps the dominant galaxy in the Virgo Cluster of galaxies. M87's diameter corresponds to a linear extension of 120,000 light years, more than the diameter of our Milky Way's disk. It fills a much larger volume, and thus contains much more stars (and mass) than our galaxy, certainly several trillion (1012) solar masses. M51 M87 The Milky Way

Galaxies with active nuclei: 

Galaxies with active nuclei The first class of galaxies with active nuclei was discovered by Seyfert (1940): Seyfert galaxies. Spiral galaxies but posess star like nuclei Strong and broad emission lines The next class of galaxies with active nuclei discovered was the radio galaxies. Sources of vast fluxes of high energy particles and magnetic fields The first quasars were discovered early 1960 Look like star but has a luminosity much greater than galaxies. Radio quiet quasars, blazars, were discovered in 1965 BL Lacertae er BL-Lac objects are the most extreme examples of active galactic nuclei. Similar to quasars but luminosity vary rapidly (days): compact objects. Optical spectra featureless and radiation strongly polarized.

Model for generating energy in AGNs: 

Model for generating energy in AGNs Massive black hole Accretion disk Collimated jets When the jet is directed towards us the luminosity increases

Supernovae: 

Supernovae Supernova occur at the end of a star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. If the star is particularly massive, then its core will collapse and a huge amount of energy is released. This will cause a blast wave that ejects the star's envelope into interstellar space. The result of the collapse may be a rapidly rotating neutron star that can be observed many years later as a radio pulsar. Supernovae are rare events in our galaxy. There are many remnants of Supernovae explosions in our galaxy, that are seen as X-ray shell like structures caused by the shock wave propagating out into the interstellar medium. A famous remnant is the Crab Nebula which exploded in 1054: pulsar which rotates 30 times a second and emits a rotating beam of X-rays (like a lighthouse).

Supernova 1987A: 

Supernova 1987A The animation illustrates the events following the supernova 1987A outburst (Large Magellanic Cloud). The blue ring is previously observed material ejected from the star thousands of years ago. The expanding orange and yellow shell is multimillion degree, X-ray emitting gas produced by the explosion. Portions of the blue ring light up when struck by the X-ray shell.

Neutron stars: 

Neutron stars Neutron stars may appear in supernova remnants, as isolated objects, or in binary systems. When a neutron star is in a binary system, astronomers are able to measure its mass. For binary systems containing an unknown object, this information helps distinguish whether the object is a neutron star or a black hole, since black holes are more massive than neutron stars.

X-ray binaries: 

X-ray binaries

Pulsars: 

Pulsars Radio pulsars were discovered in 1967. Pulsars are isolated, rotating, magnetised neutron stars. They have jets of particles moving almost at the speed of light streaming out above their magnetic poles. Crab Nebula: example of a neutron star formed during a supernova explosion. Figures show the diffuse emission of the Crab Nebula surrounding the bright pulsar in both the "on" and "off" states, i.e. when the magnetic pole is "in" and "out" of the line-of-sight from Earth. The period is 33 ms.

Vela Pulsar: 

Vela Pulsar Chandra's image of the Vela Pulsar shows a dramatic bow-like structure at the leading edge of the cloud, or nebula, embedded in the Vela supernova remnant. As indicated by the arrow, the jets point in the same direction as the motion of the pulsar. The swept-back appearance of the nebula is due to the motion of the pulsar through the supernova remnant. The last few frames of this animation show the region of space around the rapidly rotating neutron stars in the Crab Nebula (left) compared with Vela (right). The inner Crab ring is 1 light year in diameter; in Vela it is 0.1 light year.

Gamma Ray Bursts: 

Gamma-ray bursts are short-lived bursts of gamma-ray photons. At least some of them are associated with a special type of supernovae, the explosions marking the deaths of especially massive stars. Lasting anywhere from a few milliseconds to several minutes, gamma-ray bursts (GRBs) shine hundreds of times brighter than a typical supernova. GRBs are detected roughly once per day from wholly random directions of the sky. GRBs were discovered in the late 1960s by U.S. military satellites which were on the look out for Soviet nuclear testing in violation of the atmospheric nuclear test ban treaty. Gamma Ray Bursts

Model for GRBs: 

Model for GRBs The star -- containing about 10 solar masses worth of helium, oxygen and heavier elements -- has depleted its nuclear fuel. This has triggered a Type Ic supernova / gamma-ray burst event. The core of the star has collapsed, without the star's outer part knowing. A black hole forms inside surrounded by a disk of accreting matter, and, within a few seconds, launched a jet of matter away from the black hole that ultimately made the gamma-ray burst. The jet (white plume) is breaking through the outer shell of the star, about nine seconds after its creation.

The interstellar medium: 

The interstellar medium The region between the stars in a galaxy have very low densities (they constitute a vacuum far better than can be produced artificially on the surface of the Earth), but are filled with gas, dust, and charged particles. Approximately 99% of the mass of the interstellar medium is in the form of gas with the remainder primarily in dust. The total mass of the gas and dust in the interstellar medium is about 15% of the total mass of visible matter in the Milky Way. Of the gas in the Milky Way, 90% by mass is hydrogen. The gas appears primarily in two forms 1. Cold clouds of atomic or molecular hydrogen 2. Hot ionized hydrogen near hot young stars Interstellar dust grains are typically a fraction of a micron across (approximately the wavelength of blue light), irregularly shaped, and composed of carbon and/or silicates. These dust clouds are visible if they absorb the light coming through them. The clouds of cold molecular and atomic hydrogen represent the raw material from which stars can be formed in the disk of the galaxy if they become gravitationally unstable and collapse.

Example: Orion Nebula: 

Example: Orion Nebula The Orion Nebula is relatively nearby, about 1500 light years away in the same spiral arm of the galaxy as our own Sun.

Example: The Pleiades Cluster: 

Example: The Pleiades Cluster The Pleiades Cluster is a young cluster of predominantly blue stars that is visible to the naked eye. There is still some dust left from the nebula in which they formed, and light reflecting from that dust causes the blue haze around each star of the cluster.

Magnetic Fields: 

Magnetic Fields The Milky Way galaxy contains an ordered, large-scale magnetic field of the value of about 4 mGauss (Earth's field at ground level is about 1 Gauss.) Observation methods: analysis of starlight polarization, modeling pulsar or Faraday rotation, Zeeman splitting of atomic or molecular lines, radio synchrotron emission of electrons A spiral galaxy like the Milky Way has three basic components to its visible matter which include the disk (containing the spiral arms), the halo, and the nucleus or central bulge. Because of the varying density in the galaxy's components, the magnetic field has a range of values. Magnetic field derived from galaxy simulation overlaid on the galaxy NGC 4151. The blue 'ribbons' are components of a vertical magnetic field while the green arrows depict both the axisymmetric and bisymmetric magnetic fields observed in galaxies of this morphological type. Estimations for extra-galactic magnetic field varies from 1 nGauss to 100 nGauss The strongest, naturally-occurring, fields are found on a new kind of neutron star called a magnetar. These fields can exceed 1015 Gauss.

Dark matter: 

Dark matter The basic principle for observations is that if we measure velocities in some region, then there has to be enough mass there for gravity to stop all the objects flying apart. Velocity measurements -> the amount of inferred mass is much more than can be explained by the luminous stuff -> Dark Matter Precise measurements of the cosmic microwave background -> dark matter makes up about 25% of the energy budget of the Universe; visible matter in the form of stars, gas, and dust only contributes about 4%. The leading candidate for this "dark matter" is the neutralino, the lightest supersymmetric particle. On astrophysical scales, collisions of neutralinos with ordinary matter are believed to slow them down. The scattered neutralinos, whose velocity is degraded after each collision, may then be gravitationally trapped by objects such as the Sun, Earth, and the black hole at the center of the Milky Way galaxy, where they can accumulate over cosmic time scales.

Acceleration of charges particles: 

Acceleration of charges particles The specific features of particle acceleration: A power law energy spectrum: dN(E) E-x dE where x is about 2.2-3. The acceleration of cosmic rays to energies of about 1020 eV The acceleration mechanism should result in chemical abundances of cosmic rays which are similar to cosmic abundances of the elements

General principles of acceleration: 

General principles of acceleration The acceleration mechanisms may be classified as dynamic, hydrodynamic and electromagnetic. Dynamic: Acceleration takes place through the collision of particles with clouds. Hydrodynamic: Acceleration of whole layers of plasma to high velocities. Electromagnetic: Particles accelerated by electric fields (magnetospheres of neutron stars). Acceleration of particles in electric and magnetic field: d/dt (gmv) = e(E+v x B) Static electric fields difficult to maintain due to the very high conductivity of ionised gases. Acceleration mechanism can only be associated with non-stationary electric fields. Static magnetic fields don’t do any work but if the magnetic field is time-varying work is done by induced electric field. Recent years: most effort to study particle acceleration is strong shock waves.

Slide29: 

Energy increased when passing the chock front Maximum energy obtained when particles confined in the acceleration site u R g = p/ qB < L Þ large dimension or strong B Þ 10 15 eV 1 pc B = 3 m G Supernova remnant Þ For energies of 1020 eV a chock of 1 Mpc needed ! Fermi mechanism (E. Fermi, Phys. Rev. 75 (1949) 1169)

Slide30: 

Candidate for acceleration up to extreme energies

Slide31: 

Shell-type supernova remnants Non-thermal radiation (radio to X-rays) -> synchrotron radiation of accelerated electrons Direct evidence for acceleration of electrons at outer shock from hard X-rays Chandra (SN1006) Supernova remnants are the most likely source of galactic cosmic rays below the knee : 10% of the mechanical energy from supernovae explosions matches the power needed to maintain the cosmic ray flux in the Galaxy

Slide32: 

- Neutron stars = rotating magnets Þ différence in voltage B Acceleration by electrostatic machines Pulsars as cosmic accelerators Huge magnetic fields, fast rotation needed

Synchrotron radiation: 

Synchrotron radiation High-energy e± (energy Ee) in a magnetic field B, emit preferentially at « critical energy » Ec (a = angle between B and electron velocity) 10 GeV electrons radiate -> radio 100 TeV electrons radiate -> X-rays

Inverse Compton radiation: 

Inverse Compton radiation Compton effect (g+e -> g +e) but in a frame where: High-energy electron + soft photon -> High-energy photon + electron Kinematics :

Hadronic processes: 

Hadronic processes Challenge for g-ray astronomy : are g -rays from leptonic (electrons) or hadronic (π0-> g g) origin ?

The Crab nebula: 

The Crab nebula Two components Synchrotron (from radio to few MeV) Inverse Compton (GeV to 100 TeV) Electrons accelerated to PeV; B≈10 nT

Production of particles and radiation by cosmic accelerators: 

Production of particles and radiation by cosmic accelerators Acceleration of charges particles Production of gammas and neutrinos in the radiation and gas around the accelerator

Exotic particles producing cosmic rays ?: 

Exotic particles producing cosmic rays ? Neutralinos and other exotic particles -> gammas, neutrinos Anti-matter

Propagation: The Greisen-Zatsepin-Kuzmin (GZK) effect: 

Propagation: The Greisen-Zatsepin-Kuzmin (GZK) effect Nucleons can produce pions on the cosmic microwave background nucleon  sources must be in cosmological backyard

Attenuation of gamma rays: 

Attenuation of gamma rays Pair production -> TeV photons are abserbed on infrared light, PeV photons on the CMB, EeV photons on radio-waves. Origin of infrered light: light emitted by galaxies since their formation, re-processed by dust and redshifted due to the expansion of the Universe Measuring the intensity of extragalactic background light is very difficult due to the presence of very high foregrounds (Solar system, Galaxy).

Slide41: 

g-ray absorption length vs. g -ray energy TeV 1 Mpc Only neutrinos propagate without attenuation !

Slide42: 

Effects of magnetic field Ultra-high energy cosmic rays point to sources. They are not confined to our Galaxy: extra-galactic visibility. Cosmic rays <1018 eV are confined to our Galaxy for about 107 years !

Conclusions: 

Conclusions Cosmic ray Physics started 1912 when Victor Hess discovered that mysterious radiation is coming from space. The observation of cosmic rays has potential for important discoveries in Astrophysics, Particle Physics and tests the Physics laws in extreme conditions. The observation of cosmic rays on Earth is not trivial: They are attenuated in the CMB and other radiation and matter in the Universe. They can be deviated in magnetic fields. They are rare.