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Plasma universe

Plasma universe. Fluctuations in the primordial plasma are observed in the cosmic microwave background. ESA Planck satellite to be launched in 2007. Data from WMAP of NASA. Shock wave from a dying star. Accretion disk around a black hole: MHD in general relativity regime. Neutron stars.

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Plasma universe

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  1. Plasma universe Fluctuations in the primordial plasma are observed in the cosmic microwave background ESA Planck satellite to be launched in 2007 Data from WMAP of NASA Shock wave from a dying star Accretion disk around a black hole: MHD in general relativity regime

  2. Neutron stars - Radius ~10 km - Mass 1.4 Msun - Born from core collapse supernova (or possibly from white dwarf accreting mass from companion; Type Ia supernova) - Spindown and cooldown in ~107 years, after which difficult to observe (faint) - Highly magnetised neutron stars (B ~1011 T) are called magnetars

  3. Neutron star formation - Massive star’s core burns into iron - Iron core collapses. Angular momentum conservation causes rotation to increase, and rotation is also differential. BA=const causes existing magnetic field to multiply. - When neutron star density reached, gravitational collapse energy has heated matter to ~0.1 fraction of its rest mass ( ~ 100 MeV, 1012 K, per nucleon) - URCA-process cooling, T8 - Indirect URCA cooling, T6 - Convection due to temperature and lepton number gradients (density so high that neutrinos trapped inside core) ==> dynamo action, even larger B-field - Radiative cooling, T4 - Dynamo action takes ~30 seconds

  4. Neutron star life - Initially (most probably) rapidly rotating, ~1 ms - Spindown due to magnetic breaking (dipole radiation) - Spindown rate depends on strength of magnetic field (this is the main reason we know the values of the fields) - Some modest decraese of the magnetic field may also occur (this is not well known) - Neutron star magnetosphere contains electron-positron plasma, if the rotation rate is high enough - Somehow, this plasma produces coherent radio emission ==> pulsar - When rotation rate decreases below critical limit, radio emission stops, after which detection is only possible by thermal X-rays (difficult) - Irregularities: Glitches (abrupt spinrate changes), Starquakes, Decoupled rotation rates of superfluid neutrons and iron lattice in the crust

  5. Magnetars (magneettitähdet) - Very highly magnetised neutron stars - Strong magnetic breaking, rapid spindown (~10000 years), easily observable (=”live”) only short time, therefore probably much more common than low number of known examples (~ 10) would indicate - Starquakes and glitches produce gamma ray bursts. The most energetic ones (gamma flares) are so strong that they increase conductivity of Earth’s ionosphere from galactic centre distance (10 kpc) - “Soft gamma-ray repeaters” (SGRs) and “anomalous X-ray pulsars” (AXPs) - Biosphere-killing potential of the same order of magnitude as that or supernovae and gamma ray bursts (?) - Short gamma ray bursts (GRBs) may be due to magnetar gamma flares

  6. Neutron star magnetospheres Fast rotating neutron stars can be observed as pulsars (fastest ones about 1 ms) → speed of light limits the size of the pulsar Very high energies → quantum effects e.g., e– - e+ pair production and annihilation: e– + e+ → 2  (511 keV gamma rays). Plasma is necessary for radio emission.

  7. Pulsar model

  8. Neutron star observational issues - Gravitational redshift - Dependence of electron energy levels and ionisation potentials on magnetic field (generally, they increase in high field) ==> difficulty of doing spectral analysis - Recent indications for “solar-type”, non-dipolar and complex, locally strong magnetic fields. Magnetar-class fields of 1010-1011 T may occur locally even on normal neutron stars (?) - Magnetic dipole radiation (note: NOT the same as pulsar radiation, which has higher frequency) lower than any plasma frequency around ==> it must heat the surrounding plasma (??)

  9. Pulsar statistics - Spindown: motion to the right - The higher the magnetic field, the faster the spindown → magnetars observable only for ~104 years here - normal pulsars observable for ~107 years - Critical field: electron Larmor radius equal to its deBroglie wavelength → photon splitting, possible disappearance of e+e- plasma from high-field region - the Galaxy may contain millions of dead magnetars

  10. Equation of state is unknown!

  11. Accretion to a compact object

  12. Millisecond pulsars - Very high rotation rate (~1 ms) - Very slow decline of rotation rate ==> “weak” magnetic field - Always (?) in binary star systems Scenario: - Double star, heavier partner undergoes supernova and becomes neutron star. Probably it has time to slowdown and “die” (107 years) while companion still in main sequence - Lighter partner becomes red giant, fills his Roche limit ==> mass flow, accretion disk - The SMALLER the magnetic field, the SMALLER the corotating inner magnetosphere, the HIGHER the Keplerian angular velocity at the corotation boundary and the HIGHER the spinup effect of mass accretion

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  14. The End

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