In General > s.a. black holes [alternatives]; black-hole phenomenology and types.
* Idea: Objects characterized by pointlike appearance (almost stellar, earlier called quasi-stellar objects or QSOs) and large redshifts (peaking at z ~ 2).
* Nature: They are almost certainly brilliant luminous cores of galaxies, powered by infalling matter.
* Evidence: Other galaxies have similar central engines, with a wide range of luminosities, and all quasars within z ~ 0.7 show a faint fuzzy nebulosity, which often resembles a normal galaxy in appearance and spectrum.
* Energy source: Cannot be just nuclear reactions, and the most attractive possibility is the presence of large (~ 10 MSun) black holes, with matter falling into them and converting up to 50% of its mass into radiation.
* Interactions: The fraction of them in interaction with other galaxies is far greater than the corresponding fraction for all galaxies; This indicates that the presence of a quasar nucleus is strongly related to the interaction with another galaxy; The mechanism could be that if there is already a compact massive nucleus, matter coming from the other, smaller galaxy could be funneled into it.
* Puzzle: 1996, Some quasars seem to be (visually) associated with other galaxies, but have a very different redshift; No good explanation has been found yet.

@ General, reviews: Weedman 86 [III]; Rech(92)oct, p1118; Disney SA(98)jun; Osmer IAU-ap/99; Lacy ap/06; Makarov a1202-conf [quasometry].
@ History: Kellermann JAHH-a1304; Hazard et al IAU(14)-a1412 [discovery of the first Quasar 3C273]; Kellermann IAU(14)-a1412; Antonucci a1501 [and AGN, unsatisfactory progress in understanding].
@ Unconventional redshift interpretation: Arp et al ap/05 [periodicities]; Arp a0711 [evolving intrinsic redshift]; Hartnett ASS(08)-a0712, Hartnett & Hirano ASS(09) [periodicities].
@ Other unconventional: Moret-Bailly ap/03, ap/04 [as neutron stars!].
@ Related topics: Dau et al PRL(12)-a1204 [using quasars as standard clocks for measuring redshifts].
> Related topics: see cosmic strings [quasar alignment].

* Idea: Galactic miniatures of the far more distant quasars, obtained when accreting neutron stars eject relativistic particles orthogonal to the accretion disk, instead of confining disk-material down to the magnetic poles and creating the two emitting caps typical for a X-ray pulsar.
@ Reviews: Ribo ASP-ap/04; Massi Hab(05)ap, ap/06-proc; Mirabel PoS-ap/07.

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