Plasma universeFluctuations 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 starAccretion disk around a black hole:

MHD in general relativity regime

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

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

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 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 (??)

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

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” (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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The End