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The Astrophysical Jets – After 30 Years of Deliberation THE ASTROPHYSICAL JETS { AFTER 30 YEARS OF DELIBERATION Wolfgang Kundt Argelander Institute of Bonn University Auf dem Hugel¨ 71, D-53121 Bonn, Germany Abstract An update is presented of my 2004 semi-analytical model with Gopal Krishna for E x B-drifting jets, which may well describe sat- isfactorily all the astrophysical jet sources, or bipolar flows, both on galactic and on stellar scales. 1 Introduction Jet sources have been discovered in the sky, and mapped since more than 30 years, beginning at radio frequencies, closely followed by optical frequencies, then X-rays and γ-rays up to GeV energies, and recently even up to TeV energies, or even . PeV energies! Whilst more and more morphological and temporal details have been elaborated, the modes of their generation, propagation, termination, and evolution have found deploringly diverging treatments in the extended literature. This decades-long stagnation of in- sight, it appears to me, is predominantly due to the black-hole dictatorship in present-day astrophysics: Black Holes (BHs) lack persistent, time-varying magnetic fields (for pair formation, and for their post-acceleration via an outgoing strong wave), and lack quasi-static (high-density) deLaval nozzles for the formation of a pair of supersonic antipodal jets { as opposed to fast- rotating magnetized stars inside shearing accretion disks, or differentially rotating magnetized coronas of central galactic disks which have been the preferred jet sources in Kundt & Gopal-Krishna [1980, 2004] as well as in 1 Blome & Kundt [1988], and in Kundt [1979, 1989, 1996, 2001a,b, 2002, 2005, 2009a,b], to be revisited in section 4. In my mother language: Schwarze L¨ocher schlucken, sie spucken nicht. This compact review of jet formation will begin with a listing of the wide range of observed jet sources, in section 2, grouping them into a 4-headed family according to their different central engines: (a) newborn stars, (b) forming white dwarfs, (c) middle-aged binary neutron stars, and (d) nuclear- burning centers of galactic disks. Note that these four source types are expected to anchor a rapidly corotating transverse magnetic moment, whilst the often proposed (stellar-mass) `BH-Candidates' may have been mistaken for neutron stars inside of massive accretion disks, and the `supermassive BHs' at the centers of galaxies mistaken for nuclear-burning central galactic disks (BDs). Section 3 will collect a number of plausible constraints on a jet source to function, and sort between viable and non-viable mechanisms for their real- isation. The quasi-unique analytical class of jet solutions found in [Kundt & Krishna 2004] will then be reviewed in section 4, and its key features summarized in section 5. Quite similar approaches have been taken by Phil Morrison [1981], and by Peter Scheuer [1996], who are both, unfortunately, no longer with us. 2 The Bipolar-Flow Family Even though the astrophysical jet sources range through huge factors in fsize, age, power, mass(CE)g, CE := central engine, viz. range through respective factors .f108,107,109,109g, they appear astonishingly similar in their essential properties such as the jets' opening angle Θ, the jet/core power ratio, maximal speed, morphology, stability, spectrum, and variabil- ity. They tend to be divided into `micro-quasars' and `quasars' { the prefix \micro" alluding to a typical discriminating factor of 106 in their listed properties { a classification which essentially agrees with `stellar' and `galactic' CEs. Here is a table of the complete family of Jet Sources, or Bipolar Flows (BFs): Newborn Stars (YSOs) Forming White Dwarfs (inside PNe) Elderly Binary Neutron Stars Centers of Galactic Disks (AGN) For an easier comparison of the subsequent modeling with the best- studied astronomical jet sources, let us look at a few outstanding represen- tatives of the four classes: (a) Newborn stars, or young stellar objects (YSOs), tend to emit pre- dominantly thermal spectra, hence look often rather different from their more powerful and larger relatives of the BF family. Yet as already stressed in earlier publications, a few exceptions exist which look exactly like minia- ture copies of their bigger relatives, e.g. like fast expanding radio triples, of age . 103yr, see Blome & Kundt [1988], or Kundt [1996, 2001, 2002, 2005]. New is last year's discovery of half a dozen brown dwarfs with jets [Whelan et al 2009]: Even such YSOs, of subsolar mass, have strong enough magnetospheres in fast enough corotation to blow (feeble) jets. (b) Forming white dwarfs, inside planetary nebulae (PNe), have various morphologies, but at least some of them show clear evidences of feeble jets near their symmetry axes, see [Kundt 1996], and indications of two antipo- dal elongated lobes, and their various morphologies cannot be understood without multiple plasma components of different densities in extended in- teraction. Also, an increasing number of cataclysmic variables is joining the jet set. (c) This class, of BFs powered by elderly neutron stars, is likewise known since more than 30 years, with SS 433 as its most powerful, and most exotic representative: SS 433 is particularly famous for its multiple, transrelativis- tic and almost periodic optical and X-ray emission lines, which I understand as multiply excited recombination lines from dragged-along channel-wall ma- terial of the innermost parts of its precessing jets [Kundt 1996, 1998, 2001, 2005]. The channel-wall material may well stem from the wind of its (or- dinary) stellar companion. Its controversial distance { of 3 kpc { has been recently challenged by Lockman et al [2007], a paper with whose con- clusions I disagree: the 42 km/s association with W50 proposed by Dubner et al [1998] corresponds to a minimum of 21cm-line column depth in both emission and absorption, hence to a hole in HI, plausibly created by the SN. Just recently, Pakull et al [2010] have discovered a 20 times older brother of its kind, `nebula' S 26 in the outskirts of the Sculptor galaxy NGC 7793, which is similarly impressive even if somewhat fainter than SS 433. The authors may have overestimated its mechanical power by assuming that its lobes were filled homogeneously with (optically) radiat- ing matter, rather than with small-filling-factor filamentary inclusions, at about 103times higher densities, by 103times less matter, and therefore with 103times less mechanical power than stated. By taking care of a filling fac- tor f t10−3 of the optical source in its lobes, the properties of S 26 conform nicely with those of all the other class-(c) sources. With the probable exception of our Galactic center, neutron stars are the only jet class with central engines which have shown (eight cases of) emission of the 511 keV e-pair annihilation line, redshifted by some 7% [Kaiser & Hannikainen 2002], an indication of significant local pair excess. There is also narrow, and very broad, and partially redshifted emission of the 511 keV line from a vicinity of Felix Mirabel's `great annihilator' [1998]. Interesting, and still poorly understood are the frequently reported time- periodic motions of X-ray spectra of class-(c)-sources in the intensity-vs- hardness plane, and of their correlations with radio outbursts, and with flaring jet formation, on varying time scales between weeks and years, which take the shape of a repeatedly traversed turkey head, [K¨ording et al 2006]. They should eventually allow us to get a deeper insight into the quasi- periodic physical processes taking place near the jets' CE. Similar quasi- periodicities take place in the AGN sources, though on distinctly longer time scales, and detected in different frequency ranges [K¨ording et al 2008]. (d) Many new discoveries have been made relating to those luminous `un- resolved massive objects' (UMOs) at the centers of massive galaxies often called `supermassive black holes', or simply `active galactic nuclei' (AGN), which may instead be the dense, nuclear-burning centers of their massive disks. Their best known representative is the source Sgr A* at our own Galactic center, whose supposed BH nature has received another eight fierce- ful blows during the past four years. Serious doubts on its BH interpreta- tion were already expressed in [Kundt 1990, 2001b], among others because of its strong wind, mapped in the Brackett α and γ lines, of mass rate −2:5 3 10 M /yr, speed .10 km/s, which is seen to blow off tails from wind- zones of &8 stars within 1 lyr from Sgr A*. These doubts were enhanced when Aharonian et al [2004] detected Sgr A* in emission at TeV energies, because the temperature of an accreting BH (of mass M) is predicted to 1=4 be below 1 keV(M /M) , controlled by the Eddington limit on its lumi- nosity. Then came the news from Frank Eisenhauer, in his 16 Nov. 2007 Bonn colloquium, that the 16 yr-Kepler ellipse of the star S2 (around Sgr A*) did not close, by some 3 degrees, some 102:2 times larger than the general-relativistic periastron precession rate, cf. [Gualandris et al 2010] : Did the non-pointlike gravity of a massive central disk make itself felt? Such a high-density, flat central mass array had already indicated its presence by a monotonicly increasing estimated mass of Sgr A*, between 2003 and 2007, 6:41 6:58 6:63 during increasing approach, from 10 to 10 M , or even to 10 M , as well as by an increasing estimated distance d of Sgr A*, towards 8.33 kpc, in mild conflict with other, independent distance estimates, of d .8.1 kpc; (d allows the conversion of angular velocities into linear transverse velocities of a test star). A fourth, and fifth orbital anomaly of star S2 were reported by Gillessen et al [2009]: When approaching its peri-astron in 2002, S2 flared by half a magnitude, and six successive position measurements were shifted by .10 mas towards NE, reminiscent of an IR fata morgana caused by a 12 −3 discal medium of (high) number density ne t 10 cm .
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