| 1. |
- Aalto, Susanne, 1964
(author)
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Chemistry in luminous AGN and starburst galaxies
- 2008
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In: Astrophysics and Space Science. - : Springer Science and Business Media LLC. - 1572-946X .- 0004-640X. ; 313:1-3, s. 273-278
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Journal article (peer-reviewed)abstract
- Molecular line emission is a useful tool for probing the highly obscured inner kpc of starburst galaxies and buried AGNs. Molecular line ratios serve as diagnostic tools of the physical conditions of the gas-but also of its chemical properties. Both provide important clues to the type and evolutionary stage of the nuclear activity. While CO emission remains the main tracer for molecular distribution and dynamics, molecules such as HCN, HNC, HCO+, CN and HC3N are useful for probing the properties of the denser (n greater than or similar to 10(4) cm(-3)), star-forming gas. Here I discuss current views on how line emission from these species can be interpreted in luminous galaxies. HNC, HCO+ and CN are all species that can be associated both with photon dominated regions (PDRs) in starbursts-as well as X-ray dominated regions (XDRs) associated with AGN activity. HC3N line emission may identify galaxies where the starburst is in the early stage of its evolution.
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| 2. |
- Abramowicz, Marek A, 1945, et al.
(author)
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Epicyclic frequencies derived from the effective potential: simple and practical formulae
- 2005
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In: Astrophys. Space Sci.. - : Springer Science and Business Media LLC. - 0004-640X. ; 300:1-3, s. 127-136
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Journal article (peer-reviewed)abstract
- We present and discuss a short and simple derivation of orbital epicyclic frequencies for circular geodesic orbits in stationary and axially symmetric spacetimes. Such spacetimes include as special cases analytically known black hole Kerr and Schwarzschild spacetimes, as well as the analytic Hartle-Thorne spacetime and all numerically constructed spacetimes relevant for rotating neutron stars. Our derivation follows directly from energy and angular momentum conservation and it uses the concept of the effective potential. It has never been published, except for a few special cases, but it has already become a part of the common knowledge in the field.
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| 3. |
- Alfvén, Hannes
(author)
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Annihilation model of quasi-stellar objects
- 1979
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In: Astrophysics and Space Science. - : Kluwer Academic Publishers. - 0004-640X .- 1572-946X. ; 64:2, s. 401-419
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Journal article (peer-reviewed)abstract
- The possibility that annihilation is a major source of energy in cosmic physics is discussed. Since Klein suggested that the Universe might be matter-antimatter symmetric over two decades ago, there have been a significant number of papers developing the consequences of this view. These, however, have been largely ignored in the general literature. There have also been a number of papers claiming to prove that there cannot be antimatter anywhere in the observable Universe. In the first part of this paper an assessment of the differing views is given, and it is shown that none of the arguments against antimatter is convincing. The existence of antimatter is not in conflict with any observational fact. The reason for the negative attitude towards the existence of antimatter seems to be that this view is in conflict with a number of speculative but ‘generally accepted’ theories. However, recent magnetospheric and heliospheric research, includingin situ measurements of cosmic plasmas, is now drastically changing cosmic plasma physics in a way that leads to growing scepticism about quite a few of the speculative theories.An attempt is made to develop a simple phenomenological model of QSOs based on star-antistar collisions. This model can account for such basic observational properties as the acceleration to very large (non-cosmological) velocities, the existence of broad emission lines, and at the same time narrow absorption lines with different redshifts. The absence of blueshifts is also explained. The model predicts that relatively young QSOs should be at cosmological distances whereas the old ones may very well be much closer to us than indicated by their redshift.
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| 4. |
- Alfvén, Hannes
(author)
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Double radio-sources and new approach to cosmical plasma physics
- 1978
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In: Astrophysics and Space Science. - : Kluwer Academic Publishers. - 0004-640X .- 1572-946X. ; 54:2, s. 279-292
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Journal article (peer-reviewed)abstract
- The methodology of cosmic plasma physics is discussed. It is very hazardous to try to describe plasma phenomena by theories which have not been carefully tested experimentally. One present approach is to rely on laboratory measurements andin situ measurements in the magnetosphere and heliosphere, and to approach galactic phenomena by scaling up the wellknown phenomena to galactic dimensions. A summary is given of laboratory investigations of electric double layers, a phenomenon which is known to be very important in laboratory discharges. A summary is also given of thein situ measurements in the magnetosphere by which the importance of electric double layers in the Earth's surrounding is established. The scaling laws between laboratory and magnetospheric double layers are studied. The successful scaling between laboratory and magnetospheric phenomena encourages an extrapolation to heliospheric phenomena. A further extrapolation to galactic phenomena leads to a theory of double radio sources.In analogy with the Sun which, acting as a homopolar inductor, energizes the heliospheric current system, a rotating magnetized galaxy should produce a similar current system. From analogy with laboratory and magnetospheric current systems it is argued that the galactic current might produce double layers where a large energy dissipation takes place. This leads to a theory of the double radio sources which, within the necessary wide limits of uncertainty, is quantitatively reconcilable with observations.
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| 5. |
- Alfvén, Hannes
(author)
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Hubble expansion in a Euclidean framework
- 1979
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In: Astrophysics and Space Science. - : Kluwer Academic Publishers. - 0004-640X .- 1572-946X. ; 66:1, s. 23-37
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Journal article (peer-reviewed)abstract
- There now seems to be strong evidence for a non-cosmological interpretation of the QSO redshift — in any case, so strong that it is of interest to investigate the consequences. The purpose of this paper is to construct a model of the Hubble expansion which is as far as possible from the conventional Big Bang model without coming in conflict with any well-established observational results (while introducing no new laws of physics). This leads to an essentially Euclidean metagalactic model (see Table I) with very little mass outside one-third or half of the Hubble radius. The total kinetic energy of the Hubble expansion need only to be about 5% of the rest mass energy.Present observations support backwards in time extrapolation of the Hubble expansion to a ‘minimum size galaxy’R m , which may have any value in 0Some of the conclusions based on the Big Bang hypothesis are criticized and in several cases alternative interpretations are suggested. A comparison between the Euclidean and the conventional models is given in Table III.
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| 6. |
- Alfvén, Hannes, et al.
(author)
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Inter-stellar clouds and formation of stars
- 1978
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In: Astrophysics and Space Science. - : Springer Nature. - 0004-640X .- 1572-946X. ; 55:2, s. 487-509
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Journal article (peer-reviewed)abstract
- Part I gives a survey of the drastic revision of cosmic plasma physics which is precipitated by the exploration of the magnetosphere throughin situ measurements. The ‘pseudo-plasma formalism’, which until now has almost completely dominated theoretical astrophysics, must be replaced by an experimentally based approach involving the introduction of a number of neglected plasma phenomena, such as electric double layers, critical velocity, and pinch effect. The general belief that star light is the main ionizer is shown to be doubtful; hydromagnetic conversion of gravitational and kinetic energy may often be much more important.In Part II the revised plasma physics is applied to dark clouds and star formation. Magnetic fields do not necessarily counteract the contraction of a cloud; they may just as well ‘pinch’ the cloud. Magnetic compression may be the main mechanism for forming interstellar clouds and keeping them together.Part III treats the formation of stars in a dusty cosmic plasma cloud. Star formation is due to an instability, but it is very unlikely that it has anything to do with the Jeans instability. A reasonable mechanism is that the sedimentation of ‘dust’ (including solid bodies of different size) is triggering off a gravitationally assisted accretion. A ‘stellesimal’ accretion analogous to the planetesimal accretion leads to the formation of a star surrounded by a very low density hollow in the cloud. Matter falling in from the cloud towards the star is the raw material for the formation of planets and satellites.The study of the evolution of a dark cloud leads to a scenario of planet formation which is reconcilable with the results obtained from studies based on solar system data. This means that the new approach to cosmical plasma physics discussed in Part I logically leads to a consistent picture of the evolution of dark clouds and the formation of solar systems.
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| 7. |
- Alfvén, Hannes
(author)
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On hierarchical cosmology
- 1983
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In: Astrophysics and Space Science. - : Kluwer Academic Publishers. - 0004-640X .- 1572-946X. ; 89:2, s. 313-324
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Journal article (peer-reviewed)abstract
- Progress in laboratory studies of plasmas and in the methods of transferring the results to cosmic conditions, together within situ measurements in the magnetospheres, are now causing a ‘paradigm transition’ in cosmic plasma physics. This involves an introduction ofinhomogeneous models with double layers, filaments, ‘cell walls’, etc.Independently, it has been discovered that the mass distribution in the universe is highly inhomogeneous; indeed,hierarchical. According to de Vaucouleurs, the escape velocity of cosmic structures is 102–103 times below the Laplace-Schwarzschild limit, leaving avoid region which is identified as a key problem in cosmology.It is shown that a plasma instability in the dispersed medium of the structures may produce this void and, hence, explain the hierarchical structure. The energy which is necessary may derive either from gravitation or from annihilation caused by a breakdown of cell walls. The latter alternative is discussed in detail. It leads to a ‘Fireworks Model’ of the evolution of the metagalaxy.It is questioned whether the homogeneous four-dimensional big bang model can survive in an universe which is inhomogeneous and three-dimensional.
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| 8. |
- Alfvén, Hannes
(author)
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Saturnian rings
- 1976
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In: Astrophysics and Space Science. - : Kluwer Academic Publishers. - 0004-640X .- 1572-946X. ; 43:1, s. 97-104
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Journal article (peer-reviewed)abstract
- The structure of the Saturnian rings is compared with the asteroidal belt and the relative importance of the resonance effects and the cosmogonic effects is evaluated. No visible correspondence to the Kirkwood gaps is expected theoretically, nor is there any observational evidence for such effects. The only possible resonance is the 1:1 resonance with Saturn's spin period.Cosmogonic ‘shadow’ effects are responsible for the main features of the ring structure, including Cassini's division, the limit between the B and C ring, and possibly also Guérin's division.
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| 9. |
- Alfvén, Hannes
(author)
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Solar-system history as recorded in the Saturnian ring structure
- 1983
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In: Astrophysics and Space Science. - : Kluwer Academic Publishers. - 0004-640X .- 1572-946X. ; 97:1, s. 79-94
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Journal article (peer-reviewed)abstract
- The paper is based on Holberg's analysis of the Voyager photographs in both reflected and transparent light, combined with occultation data of stars seen through the rings.Besides rapidly varying phenomena (spokes, braided ring, etc.), which according to Mendis are due to gravito-electromagnetic effects, the ring consists of abulk structure, a fine structure, and also ahyperfine structure, showing more than 10000 ringlets.The large number of ringlets can be explained by the Baxter-Thompson ‘negative diffusion’. This gives the ringlets a stability which makes it possible to interprete them as ‘fossils’, which originated at cosmogonic times.It is shown that thebulk structure can be explained by the combined ‘cosmogonic shadows’ of Mimas, the co-orbiting satellites, and the Shepherd satellites. This structure originated at the transition from the plasma phase to the planetesimal phase (which probably took place 4–5×109 y ago).Further, Holberg has discovered that the shadows are not simple void region but exhibit a certain characteristic ‘signature’. This is not yet understood theoretically.Parts of thefine structure are explained by Holberg as resonances with the satellites. Parts are here interpreted as cosmogonic shadow effects. However, there are a number of ringlets which can neither be explained by cosmogonic nor by resonance effects.The most important conclusion is that an analysis of the ring data is likely to lead to areconstruction of the plasma-planetesimal transition with an accuracy of a few percent.
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| 10. |
- Alfvén, Hannes
(author)
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The Voyager-1 - Saturn encounter and the cosmogonic shadow effect
- 1981
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In: Astrophysics and Space Science. - : Kluwer Academic Publishers. - 0004-640X .- 1572-946X. ; 79:2, s. 491-505
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Journal article (peer-reviewed)abstract
- If an electrically conducting medium (e.g. a dusty plasma) rotates around a gravitating central body, which possesses an axisymmetric dipole field, the medium is supported to two-thirds by the centrifugal force and to one-third by electromagnetic forces under the condition that the magnetic field is strong enough to controll the motion. If the electromagnetic forces disappear — e.g. by a de-ionisation of the dusty plasma — the medium will fall down to two-thirds of its original central distance. The result of this process will be a ‘cosmogonic shadow effect’ which is described in some detail.The Voyager 1/Saturn results demonstrate that the macro-structure of the Saturnian ring system can be explained as a result of this effect working at the formation of the system. The agreement between the theoretical results and the observations is better than a few percent.A similar analysis of the asteroidal belt shows that its macro-structure can also be explained by the cosmogonic shadow effect. The agreement between theory and observations is perhaps even better than in the Saturnian ring system.The observational results demonstrate that during their formation both the Saturnian ring and the asteroidal belt passed a plasma state dominated by electromagnetic effects.
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