Observational Paradoxes in Extragalactic Astronomy J. Schneider, Meudon Chargé de Recherches at the CNRS, working in ABCDE the Groupe d’Astrophysique Relativiste, at the Meudon Observatory, Meudon. France. where λ is the value of the wavelength in the Chain VV 172 (Fig. 1) the ga­ of spectral lines at the emission and λ’ laxy B has a redshift of 30 000 km/s is their value at the observer ; H is the whereas the four other galaxies have present day value of the Hubble redshifts of 15 000 km/s ; in the Sey- constant, D is the present distance fert Sextet one galaxy has a redshift and c is the velocity of light. The pro­ of 20 000km/s whereas the five other duct zc is the symbolic recession redshifts are 4 500 km/s ; in Stephan's velocity, designated often shortly as Quintet (Fig. 2) the galaxy A has a redshift. redshift of 800 km/s whereas the Here it is important to realize that others have redshifts of 6 000 km/s. measuring the distance is very diffi­ How can such large differences be cult. For a quasar (QSO) no distance explained by conventional cosmology measurement has so far been pos­ as summarized in eq. (1) ? Certainly Fig. 1 Chain VV172 of five galaxies. sible. It is assumed however that the not by orbital motions of the objects above relation holds for these objects. around each other since the escape To understand astrophysical pheno­ velocities are of the order of 500 km/s. Certain extragalactic observations, mena the following basic working hy­ By the term HD/c ? But then one must because of their paradoxical aspects pothesis is made, i.e. the present conclude that these galaxies are so constitute a great mystery to astrono­ laws of microscopic physics are the close together in the sky as a result mers. These observations, which still same in a celestical body as those we of chance only. From the density of need confirmation, do not fit the cur­ know today on the Earth. One can call galaxies in the sky, one estimates rent picture of the Universe. In parti­ this the Fundamental Hypothesis of the probality to be very small that cular, the puzzle due to the observed Astrophysics. three coincidences occur. redshifts of some galaxies and qua­ With this the whole Universe is sars for which at present there is no described and one could in principle Astronomers became aware of these explanation will be considered here. stop here. In fact, it is at this point curiosities at about the same time as Today’s conventional cosmology that things start. the discovery of QSO’s. At that time rests on the empirically derived ex­ For several years it has been the cosmological origin of the redshift pansion law of Hubble which gives for known that a few groups of gala­ of quasars was questioned. A few the redshift of galaxies and quasars xies present the curious property that astronomers assumed that there might the redshift of one galaxy differs exist a different origin to the redshift z = λ’/λ — 1 = HD/c (1), greatly from that of the others : than the Doppler effect and the cosmic expansion. To check whether different galaxies were at the same distance and thus that their cosmological red­ shifts where the same, H. Arp studied galaxies connected by luminous fila­ ments. He found that even two objects connected by a bridge could have very discrepant redshifts. In Fig. 3, where the connection is well esta­ blished, the large galaxy has a red­ shift of 8 000 km/s and the compact companion a redshift of 19 000 km/s. There exist five other possible con­ nections between galaxies and com­ pact objects (see table I). The largest difference is found for the pair NGC 4319/M205 (Fig. 4) where the galaxy has a redshift of 2 000 km/s whereas the compact object (a QSO or a N- type galaxy) has a redshift of 20 000 km/s. However these latter con­ nections are not definitively confirmed Fig. 2 Stephan’s Quintet. and a large part of the controversy * Seminar given at CERN, Geneva on 12 February 1974. concerns their existence. 6 The DEPARTMENT of PHYSICS AND ASTRONOMY of the STATE UNI­ VERSITY of LEIDEN invites applicants for a position of Lector in the Physics of Metals The position, which has tenure, is comparable to that of an associate professor. • Applicants should have a good understanding of the physics of metals and a wide experience of research in solid state physics. • The task of the lector will be to lead a research team working on prob­ lems in metal physics in the Kamerlingh Onnes Laboratory. This work comprises, at present, thermal and transport properties of alloys, opti­ cal absorption, physical metallurgy etc. and is financially supported by the Foundation F.O.M. (Fundamental Research of Matter). • Knowledge of the Dutch language is not essential. • Salary ranges, with annual increases, from about 53,000 to 76,000 Dutch guilders. • Applications, with list of publications, curriculum vitae, and the names of at least two references should be sent to the chairman of the ap­ pointment committee Prof. W.J. Huiskamp, Kamerlingh Onnes Labo­ ratory, Nieuwsteeg 18, Leiden, Holland. Information can be obtained from Dr. G.J. van den Berg, Kamerlingh Onnes Laboratory. Fig. 3 Galaxy NGC 7603 (redshift 8 000 km/s) connected by a bridge of luminous matter to a compact companion at the bottom (redshift the Hubble distance deduced from to find something new to explain 19 000 km/s). Hubble law. Surprisingly however the redshift. Some astronomers, like Arp, distance of galaxy B turned out to be have proposed to give up the Funda­ For NGC 4319/M205 Arp obtained about the same than that of galaxy A, mental Hypothesis and envisaged that six photographs with a visible con­ disagreeing thus completely with the new physical laws applied in celesti- nection but other observers did not Hubble distance since the redshift of ca'I bodies. succeed in seeing the bridges. When that galaxy is 8 times larger. On the Theoreticians also have speculated two objects with different redshifts are other hand a group of radioastrono­ about new theories to explain these connected one can ask whether it is mers from the Meudon Observatory observations. One line of sought due the high redshift object or the low made a distance determination based to Hoyle and Narliker assumes that redshift one which does not satisfy on a different method, i.e. on a statis­ the electron rest mass is not an abso- the Hubble relation (1). What is remar­ tical and empirai correlation between kable is that whenever it was possible the absolute luminosity L and content to make a decision it was the high M in neutral hydrogen of a galaxy of redshift object that did not follow the given type. Here again the distance of law. the galaxy A measured in this way was Let us now return to the Stephan's in agreement with the Hubble distance; Quintet which I mentioned at the be­ and here again the distance of a high ginning. Here it was possible to go redshift member of the group, ga­ one step further since the distance laxy C, turned out to be in complete of the galaxies has been determined. disagreement with the Hubble law.* First Arp has determined the distri­ Moreover the discrepant shift which bution of the angular size of the H was at first sight the low redshift II regions of galaxies A and B (Fig. 2). in the Quintet turned out to be in fact H regions are large spheroidal sour- the high redshift ; thus the hypothesis n that anomalous shifts were towards ces of ionized hydrogen and their the red was strongly confirmed. Since angular diameter gives a distance the extra redshift can not be absorbed indication. The distance of galaxy A by any orbiting or ejection velocity measured in this way agreed with nor by a gravitational origin, one has TABLE I Galaxy zc Connected object zc N 7603 8 000 km/s anonymous 19 000 km/s N 7320 800 N 7320 C 6 000 N 4151 900 N 4156 6 000 IC 3483 100 IC 3483 7 000 N 4319 2 000 M 205 20 000 Fig. 4 Galaxy NGC 4319 connected by a lumi- nous bridge to quasar M 205 whose redshift is Anonymous < 100 000 ? PHL 1226 120 000 ten times larger. The real existence of the * See note on page 8. bridge is still controversed. 7 lute constant but changes from place 24 - 30 July to place in the Universe. Such a 9th International Conference on the Physics of Meetings Electronic and Atomic Collisions (ICPEAC) change would shift the energy levels Seattle, Wash., USA of atoms and thus the transition fre­ R. Geballe, Department of Physics, University of quencies. This assumption however For a full list of events see the latest Washington, Seattle, Wash. 98195 does not explain why the shift is sys­ Meetings Issue of Europhysics News 5, 5 (May 1974). Notification of the meet­ 18 - 21 August tematically towards the red. Another 3rd International Conference on Vapour Growth attempt was made by J.-C. Pecker, ings announced in this issue has been and Epitaxy J.-P. Vigier et al. from Paris : they received recently. Amsterdam, The Netherlands The order of information is: date, C.J.M. Rooymans, Philips Research Laboratories, assume a new type of inelastic inter­ Bldg. WA, Eindhoven action between the photon and a new title, venue, and contact for Inform­ massive boson.