Similar effects are recorded for the fainter SS 433 : features around other spectral lines. In par­ ticular, all the satellites are blue- and red- shifted by the same amount AX/X at a A New Extraordinary given time, which is one of the main rea­ sons for interpreting the effect as due to a Object in Astrophysics Doppler shift (Δλ/λ = v/c). The simultaneous presence of a red- and Franco Ciatti, a blue-shift implies that we are observing two emitting regions, one of which is Asiago Astrophysical Observatory receding and the other approaching the observer. Moreover such large shifts re­ quire a very high value of the velocity-up to During the month of October 1980, was not completely new, several such ob­ one quarter of the , and by far theoretical and observational astronomers jects being known already. the highest value ever observed for any ob­ of many nations gathered in Rome to at­ Other groups of astronomers, Ciatti, ject inside our . tend an international meeting, sponsored Mammano and Vittone at the Asiago by the Accademia dei Lincei, with the title Observatory in Italy, and Margon with Twin Jets Model for SS 433 "SS 433: A New Extraordinary Object in several collaborators at the University of Astrophysics”. It was no aberration that California, observed SS 433 in the Autumn The most popular and widely accepted this colloquium was devoted to the study of 1978 and found quite strong emission model of SS 433 supposes that two beams of a single object, as the in question is lines at unusual positions, defying iden­ of matter are ejected from a central object certainly the most peculiar object discove­ tification with the elements usually found in opposite directions at high velocity. This red in the sky for several . In the past in stellar atmospheres. Furthermore, chan­ interpretation was first proposed by the few decades, many new types of celestial ges in intensity and wavelength were evi­ astrophysicists A. Fabian and M. Rees in object, quasars, pulsars and possibly black dent from one night to the next. For this England, and M. Milgrom in Israel. Their holes ... have been revealed: SS 433 is no reason, a systematic effort was made to considerations, based on the first scanty less important, as its properties make it follow the variations with time, until the data, still remain the basis of the model quite unique. star became too close to the Sun. which has since been developed by other Through the telescope, SS 433 appears Finally the essential features became authors. As the observed spectral features as a source of light of 15th magnitude: i.e., clear: in SS 433 the strongest emissions are rather narrow, with only a small velocity about 4000 times fainter than the faintest (due to hydrogen and neutral helium) pre­ dispersion, we must accept that the two one can observe on a clear night. It sent a triple set of lines: one of them is sta­ beams are well collimated: an angle of the lies in the of , close to tionary, near the laboratory wavelength, order of 5° being required for the cones of the galactic plane, in a region rich in stars while the other two are moving on both emitted matter. Moreover, in order to and gas and dust clouds. Twenty years sides across the spectrum. The wavelength explain the sinusoidal motion of the ago, following its observation by the variations cover a complete cycle in a "moving" lines over 165 d, we need a American astronomers C.B. Stephenson period of about 165 days, describing a modulation of the radial velocity with such and N. Sanduleak, it was included in a list sinusoidal curve of unprecedented ampli­ a period. This we deduce is caused by the of some hundreds of stars that showed tude (Fig. 1). For instance, the Hα line ejected beams tracing out a cone as they hydrogen emission lines, which usually in­ [λo = 6563 A) has two "satellites" which rotate around a fixed axis. In this way the dicate the presence of an extended enve­ reach a maximum separation of about projection of the beam velocity on the line lope of gas around the stellar body. The 900 A (one at 7700 A in the near infrared, of sight and so the recorded wavelengths number given was 433 from whence its the other at 5800 A in the yellow region). change with time. name. No other spectacular object has been found in the same list from among the Fig. 1 — Red- and blue-shifted systems of "moving" lines around (λQ = 6563 A) in SS 433, ac­ many stars of several well known classes. cording to the Asiago observations and other published data. Dashed lines indicate the best fit Subsequently, SS 433 was found and sinusoidal solution. Note the large amplitude, and the red-shift at the crossing points due to the lost several times by astronomers working relativistic in matter moving at v= c/4. at different frequencies beyond the con­ ventional "optical” region; e.g., a source of radio waves and X-rays was reported at its position in some Catalogues compiled from observations, that were both ground based and from satellites like Uhuru and Ariel 5, although positional accuracy was poor. Great attention to SS 433 was finally drawn in 1978, after the work of Canadian and British researchers, who reported a high time variability and a non-thermal emission mechanism. The precise position associated with these measurements, al­ lowed the source to be identified with the star SS 433, and this prompted optical astronomers to study its visible spectrum. The first detailed spectrogramme, obtained with the large Anglo-Australian Telescope, revealed unusual properties and provided further confirmation of its identity. However, a radio and X-ray emitting star 8 The motion of the jets from SS 433 is a precessional one, like that described by the Earth's rotational axis, and somewhat resembles that of water from a garden sprinkler. It is also important to note that the two sinusoidal curves do not cross over the stationary lines at zero velocity. The curves are bodily shifted to the red, as can be seen from computing the "barycentric" position of the blue- and red-shifted features for each date. This additional red- shift remains roughly constant with time, and amounts to more than 200 A at Hα. It can be entirely explained by the so called transverse caused by relati­ vistic time dilation, which makes moving clocks tick slower (commonly described in the "twins paradox"). In our case the clocks are replaced by the emitting atoms which are moving at high velocity, so that the spectral lines are recorded with a shift of about Δλ/λ = (v/c)2/2, quite apart Fig. 2 — Schematic picture of SS 433 inside the radio supernova remnant W 50. Its extensions, op­ from the radial velocity contributions. tical filaments, and the extended radio and X-ray structures elongated in the same direction, support Adopting the model of the precessing the model of double beam ejection. double jet, a kinematical analysis of the system has been carried out at Asiago more complex than assumed in the simple strong emission is produced also in the in­ covering data taken also by different model. ner regions. The radio data indicate a observers on 235 nights during 1978-80. In particular it seems clear that matter is distance of 3-4 x 103 (1 pc = 3.26 The motion of the spectral lines is exactly not flowing away from SS 433 continuous­ light years = 3 x 1016 m) in good agreement described by two sinusoidal curves: ly, but rather as discrete clouds of gas, like with independent estimates obtained from "bullets", each of them emerging with a the study of interstellar absorption lines in Zred = C1 + A cos and Zblue = C2-A costΦ particular velocity and at a somewhat un­ the optical spectrum of SS 433. where Z = Δλ/λ, and the suffix indicates predictable angle. Two or more pairs may This coincidence strongly supports the the direction of shift at maximum ampli­ be in evidence at a given time. An in­ idea of a physical connection between the tude. teresting feature is the persistence of spec­ two objects. Moreover SS 433 is located The angle formed by the direction of the tral features at a given wavelength for very close to the centre of the extended jets with the line of sight Ψ is derived from typically 3-4 days, during which time the source. In this case, we interpret the the expression line intensity generally fades away. These peculiar object SS 433 as the stellar rem­ cosψ = (cost cosθ + sini sinθ cosΦ), data are consistent with an individual nant (a , or possibly a black where / is the inclination to the line of sight bullet, having an emission length of some hole, depending on the mass of the pro­ of the axis of the precession cone, and 0 is 1013 m and moving at constant velocity. genitor) of a supernova which exploded a the aperture. The ambiguity between these Some consideration of the emission few 104 years ago. This age can be deduc­ angles is resolved later. A least squares fit mechanism also indicates typical dimen­ ed from the radio brightness and dimension of the data yields the following "average" sions of 101°-1011 m for the largest bullets, of W 50, if we adopt the usual model for parameters. and a density of the order of 1010 ne cm-3. the expansion of a supernova shock wave A particular type of deviation from the across the interstellar medium. W 50 thus Period P = 164.7 + 0.2 days; smooth predictable motion of the lines is a would be one of the oldest supernova rem­ ß = v/c = 0.256 ± 0.002; symmetric variation of both blue and red nants we observe, whereas the collapsed i = 78.6° ± 0.2°; curves. Over a few days the two shifts star in it would be relatively young, when θ = 20.2° ± 0.3°. change by 100 A with mirror-image sym­ compared with other members of X-ray The qualification "average" is necessary metry. This phenomenon has been record­ emitting binary systems. Only in the Crab as an evident variability is observed, in both ed several times, and it seems to be related and in Vela are neutron stars the intensity and shift, which does not to a particular phase in the 165 d period. (pulsars) of lesser age observed. always fall on the predicted curve but One first conclusion is that the antisym­ Other remarkable features of W 50 can oscillates round it without any apparent metry in the spectrum is caused by a single be considered as further support for the regularity. The lines are found inside a band physical mechanism, producing simulta­ model of a double jet from SS 433. First of about 100 A wide, and often they have a neously the same ejection and acceleration all its shape could be interpreted as the complex structure; two may appear in the on opposite sides of the central object. overlap of a circular region, centred on SS red or blue system, and sometimes also in 433, and two extensions to the east and both. This well-established finding might SS 433 as a Stellar Supernova Remnant west (the ansae, or "ears"). The orienta­ suggest that more than one pair of moving Having described the unusual pheno­ tion and width of these extensions on both elements is responsible for the observed mena seen in SS 433, let us consider its sides are in good agreement with the idea behaviour. Moreover, a kinematical analy­ location in the sky. Radio maps of the area of an interaction process taking place bet­ sis carried out night by night allows us to indicate the presence of an extended ween the relativistic jets and the surroun­ conclude that the ejection occurs with source of shell structure and with roughly ding, previously symmetric envelope, crea­ varying velocity, in the range from 0.2 to elliptical shape (1° x 1.5°). Observations at ted after the supernova event. In the same 0.3 c. Also the orientation deviates from different frequencies indicate non-thermal directions some faint filamentary nebulosi­ the predicted by up to 6-7°. We are thus radio emission from this source that was ties have been optically observed, which led to conclude that some perturbations af­ named W 50. It is thought to be a super­ are barely visible on the Palomar Sky fect the ejection mechanism, making it nova remnant, although it is not typical, as Survey plate. Whereas some authors have 9 also suggested the possibility that W 50 may result from the same activity as SS 433 (that is not necessarily implying a super­ nova for its origin), the analysis of the op­ tical spectrum (consistent with excitation by shock in a pre-compressed matter) and the morphology of the filaments, favour the supernova remnant hypothesis. This allows us to solve the ambiguity between the angles i and θ. The picture is indeed consistent with ejection occuring around i = 78°, close to the plane of the sky, and with an aperture θ = 20°. Other evidence for the reality of the jets is given by observations of the radio source SS 433 at the high resolution now at­ tainable with VLBI (Very Long Base-Line Interferometry) techniques using linked radio telescopes. The radio emission comes Fig. 3 — Possible model of SS 433 in binary system, with the relativistic jets outflowing from a thick from a compact core (less than 0.1") and undergoing precessional motion. an elongated structure (2”, that is 1016 m overall and at a distance of 3.5 kpc) which is interpreted as the double beam of relati­ fifty percent in the visible band. One dif­ luminosity is smaller by two orders of vistic matter, at a distance greater than the ficulty in discussing these data is that we magnitude. There remains, however, the optically emitting region. Its position angle are not sure where the stationary spectrum unique presence of the twin jets. coincides with the direction of the exten­ originates from: the companion star, Despite the intensive and fruitful oberva- sions and filaments in W 50. Moreover, it gaseous streams, an accretion disk, or tional efforts made over the past two years, has been possible to follow changes in the even a large region around the whole many questions about the true physical position angle of the radio source from 78° binary system. Taking into account the nature and evolutionary phase of the ob­ to 118°, in agreement with the precessional distance to SS 433, and the high obscura­ ject, are still open, and despite intensive motion occuring in the 165d period. Also, tion in that direction inside the Galaxy, we theoretical work the source of the huge the outward motion has been followed obtain a rather high total optical luminosi­ amount of energy required for the beam with time for some discrete blobs, ejected ty, of the order of Mv < — 5mag (L vis = 1030 ejection and acceleration, estimated to be at different times, each propagating with J/s) like that of an upper main sequence not less than 1031 and possibly 1033 J/s, is constant direction. star of the 0 class. Adding the photometric not known. To add to this, SS 433 has been observ­ data (similar depth of the two light It is peculiar that the relativistic gas is ed with the new Heao-2 (Einstein) satellite, minima), it seems that both components in seen only through spectral lines of low ex­ which is the most recent X-ray observato­ the system are of comparable brightness. citation like those of HI and Hel. Other ry, of good sensitivity and positional ac­ Another periodicity which coincides with questions concern the sharp collimation of curacy. The source consists of a core of 3" that of the precessional motion (165 d) the beams (for which magnetic fields, or coincident with the star (with luminosity of concerns the line intensities and the total funnelling along the rotation axis of a thick the order of Lx = 1028 J/s), and fainter luminosity. These reach their maximum disk, have been suggested) and the origin features extending at least up to ± 25' and minimum when the lines are respec­ of their 165 d precession. For this latter, from the central source (about 1018 m) in tively furthest apart and nearest together. several alternative explanations are propos­ the same direction as the radio jets. These In a model involving a bright star and an ac­ ed, including free precession of the neu­ extended X-ray cones are produced by the cretion disk of similar brightness, this tron star, relativistic Lense-Thirring preces­ outflowing matter over some hundreds of dependence would result from the varying sion of the compact object with a massive years, and are thus fairly wide since the orientation of the disk. The disk would be rotating disk, or motion of the plane of the precession effects are smoothed out. Their almost face-on at maximum separation of disk, either driven by the companion star width is possibly less than 2 x θ = 40° as if the moving lines, edge-on at their cross­ misaligned with the binary plane ("slaved the trajectories were not ballistic, owing over, while the ejection of the relativistic disk") or itself precessing under tidal forces perhaps to the interaction with the ambient jets would occur along an axis perpen­ ("master disk"). Of them all some type of medium that produces the X-ray emission. dicular to the plane of the disk (see Fig. 3). disk precession seems more appropriate as The characteristic features, discussed in An accretion disk forms in the presence it can explain the photometric variability this section, are sketched in Fig. 2. of binary mass transfer, as the angular and the observed irregularities in beam momentum of the accreting matter pre­ direction. SS 433 as a Binary System vents radial infall on to the companion. Many of these questions are connected A careful study of the stationary lines, Material in the disk that is produced, with the nature of the central object. Is this first neglected, has been carried out at the dissipates momentum by spiralling in­ a neutron star, or a more exotic ? Dominion Observatory in Canada. It has wards. This is found in many astrophysical Some of the proposed models for SS 433 revealed a clear wavelength oscillation with objects such as dwarf novae and X-ray postulate indeed the presence of a black a period of 13.2d indicating small radial emitting binaries. In our case, the mass loss hole, and the ejected beams are replaced velocity variations (of the order of may, in principle, be provoked by the by a ring of matter around it. In the ring, a ± 73 km/s). Photometric observations strong stellar wind from the bright compa­ high keplerian velocity is attained, and the secured by several groups have also shown nion star. Accretion is likely to occur at a emission from two opposite points repro­ a modulation with the same 13d periodici­ supercritical rate, which would favour the duces the observed curves for the moving ty, superposed on other irregular light formation of a large and thick disk and from lines. variations. this aspect, SS 433 turns out to be not so Such a ring would have to be small, and The mean light curve has a double peak­ different from other known binaries with a one has then the difficulty in these models ed shape, with total amplitude of about collapsed component, although its X-ray of explaining the high luminosity in the 10 lines, unless thermal emission is replaced European Journal of Physics by a coherent (lasing) mechanism. Also the Editorially, Volume 1 of the European Journal of Physics is complete and Number 4 should be low temperature in the relativistic regions published in the very near future. To show more clearly the scope of this journal of the European puts constraints on their distance from the Physical Society, aimed at physicists in the higher teaching establishments, we reproduce central source, which in turn would require below the titles of the articles in Numbers 3 and 4 (omitting the regular features such as News, a very high mass for the black hole. More- Book Reviews and Letters). would be a young active neutron star, or­ biting around an early type evolved compa­ Volume 1 Number 3 1980 nion, accompanied by a thick accretion An electrical network analogue of vibrations of a linear lattice. disk. In this scheme, the effects of a Nuclear statistics with a "poor man's detector": a laboratory experiment. systematic time delay for the light travel Induced electromotive forces. should be observable between the two Rayleigh's electrified water drops. emitting regions. Variations should indeed Ondes de choc et sillage. first be recorded from the blue-shifted A generalisation of the Ehrenfests' wind-tree model. Diffusion as an example of entropy increase and the associated lost opportuni­ system, formed closer to the observer, and ty to perform work. the delay between the two systems should Wavefront dislocations in the Aharonov-Bohm effect and its water wave vary systematically throughout the 165d analogue. period. Although this is not clearly visible in Non-linear partial differential equations in physics: 1. Earlier progress. the described line variations, an analysis The symmetry property in the Hilbert space formulation of quantum mechanics. applied to the whole sinusoidal curves Obtención de relaciones funcionales. seems to indicate that statistically signifi­ Two-dimensional vector algebra: application to plane fluid flow and horizontal cant differences do exist. A separation bet­ winds. ween the two regions of the order of ± 345 Electromagnetism using bivectors. astronomical units (± 5 x 1013 m) has been A general equation for the Doppler effect. indicated, but with a still rather high Volume 1 Number 4 1980 associated error. A project laboratory experiment on digital electronics, physics demonstrations on a microcomputer. Numerical methods and physics instruction. Double Jets in Other Astrophysical Teaching Monte-Carlo simulation with pocket calculators. Objects Teaching physics out of a bag of marbles. The probable presence of a double jet Tuneable half-wave plates: an exercise on the Poincaré sphere. from SS 433, besides its obvious intrinsic - introductory courses in astrophysics. interest, could be stimulating for the study En attendant Debye... Non-linear partial differential equations in physics: II. Recent advances. of very different objects, like of Plane waves and wave packets in elementary quantum mechanics. quasars which present two extended and Exact Aharanov-Bohm wavefunction obtained by applying Dirac's magnetic opposite radio lobes. The formation of phase factor. such lobes is also interpreted in terms of The Wigner function: I. The physical interpretation. the ejection of high speed particles, but on Eloge des théories fausses. a much larger energy and dimension scale. Anyway, the possibility is now eagerly be­ ing studied that SS 433 may be a reduced New I.O.M.s New Honorary Members: P.A.M. Dirac and Peter L. Kapitza version of the same process. If a single New Associate Members mechanism could be established which can Category 4A Riso National Laboratory, Roskilde, Denmark (Sw.Frs. 1.000. — ) work at different scales, SS 433 would help I.-G. Koh, Seoul, Korea General Electric Co. Ltd., Hirst Research Centre, Wembley, UK J.-P. Swings, Cointe-Ougrée, B (Sw.Frs. 2.500.-) in understanding the nature of the ejection M.Q. Tran, Lausanne, CH phenomena from active nuclei of galaxies. Category 4C German Physical Society Polish Physical Society SS 433 remains for the present unique. W. Arnold, Saarbrücken G. Bialkowski, Warsaw Belgian Physical Society W. Biem, Giessen K. Chalasinska-Macukow, Only one candidate source, CIRCINUS J. Ghijsen, Namur H. Bilz, Stuttgart Warsaw X-1, shows radio, X-ray and optical emis­ J.-P. Lagnaux, CERN H.-W. Drawin, Fontenay-aux-Roses, F H. Cofta, Poznan sion but the signature of relativistic motion Bulgarian Academy of Sciences W. Gunsser, Moorrege S. Gogolewski, Zielona Gora is missing. Other sources nevertheless M. Georgiev, Sofia H. Meuth, Seattle, USA M. Grynberg, Warsaw Danish Physical Society E.D. Mshelia, Maiduguri, Nigeria A. Hennel, Warsaw deserve further study. If SS 433 really is an G. Ottersbach, Haan E. Kluk, Katowice early phase in the evolution of a binary J. Als-Nielsen, Roskilde T. Andersen, Aarhus J. Pelzl, Bochum W. Majewski, Warsaw system with a collapsed component, its K. M. Bisgaard, Genthofte E. Preuss, Bonn J. Malecki, Poznan J. Pietrzak, Poznan large energy and mass requirements would B. Elbek, Roskilde Italian Physical Society P. Touborg, Odense M. Surma, Poznan imply that this phase of its evolution would A.G. Cavaliere, Rome T. Szoplik, Warsaw necessarily be short lived. It may therefore Eötvös Lorand Physical Society M. Masetti, Bologna A. Szymanski, Rzeszow be the rare example of a still undetected Z. Horvath, Budapest S. Szymura, Czestochowa phenomenon. Z. Kocsis, Veszprém The Netherlands' Physical Society H. Wrembel, Slupsk Z. Szilvassy, Balatonfured E. Barbian, Nieuwegein B. Wyslocki, Czestochowa In the relatively short time since the Finnish Physical Society H. de Kluiver, Utrecht A. Ziabicki, Warsaw discovery of its extraordinary properties, K. Eskola, Helsinki F. M. Mueller, Nijmegen Swedish Physical Society SS 433 has already been the subject of P. Ketolainen, Joensuu M. Venema, Nieuwegein K.-G. Rensfelt, Bromma J. Tuominen, Helsinki more than 150 papers and scientific com­ Physical Section, Union of Yugoslav S. Wahlborn, Täby munications. If the observational and inter­ Hellenic Physical Society Societies of Mathematicians, Physi­ Swiss Physical Society pretative efforts continue with the same in­ J. Spyridelis, Thessaloniki cists and Astronomers J. Buttet, Lausanne tensity over the next years, we may reaso­ The Institute of Physics S. Savic, Belgrade A. Chatelain, Lausanne nably hope to obtain a better insight into its P.J. Duke, Warrington Y.S. Sayasov, Fribourg W. Eissner, Warrington Spanish Royal Society of Physics Turkish Physical Society physical nature and disclose the mecha­ E. Jones, Coppet, CH and Chemistry M.E. Özsan, Ankara nism which makes this star so unusual and P. Krejcik, Darmstadt, D J.R. Sanmartin, Madrid M. Tomak, Ankara exciting. T.J. Quinn, Sèvres, F V. Vento Torres, Saclay, F C. Yalcin, Ankara 11