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 - Radius ~10 km - Mass 1.4 M sun - Born from core collapse supernova (or possibly from white dwarf accreting mass from companion; Type Ia supernova) - Spindown and cooldown in ~10 7 years, after which difficult to observe (faint) - Highly magnetised neutron stars (B ~10 11 T) are called magnetars

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, K, per nucleon) - URCA-process cooling, T 8 - Indirect URCA cooling, T 6 - Convection due to temperature and lepton number gradients (density so high that neutrinos trapped inside core) ==> dynamo action, even larger B- field - Radiative cooling, T 4 - Dynamo action takes ~30 seconds

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

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

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.

Pulsar model

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 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 (??)

Pulsar statistics - Spindown: motion to the right - The higher the magnetic field, the faster the spindown → magnetars observable only for ~10 4 years here - normal pulsars observable for ~10 7 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

Equation of state is unknown!

Accretion to a compact object

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” (10 7 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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The End