spiral structure Matter ghost matter astrophysics.6:
Spiral structure.(p10)
- Impact of the different parameters.
As mentioned previously, the values of parameters are sharp. Going too far from them, and the spiral structure will no more appear. No equilibrium will be reached. We tried to compute several simulations around these optimal settings. Let us sum up here our empirical experience:
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The epicyclic frequency runs the numbers of the arms. A value w = 1 gives a two-arms structure, while = 2 gives four arms. When it lies between two integers the spiral structure becomes very uncertain.
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The ratio of negative to positive mass m controls the curvature of the arms. The structure of the former example corresponds to = 3.
Under = 3, the halo is unstable and dissipates before a spiral structure appears. It means that dissipative process (dynamic friction) heats the positive matter, which escapes through the halo.
For values over 3 the galaxy will be more and more compact. A steering-wheel appears around five. A barred spiral complete this structure. For higher masses ratio m the cluster is too much under pressure and no spiral structure seem to be viable (but, as pointed out earlier this could be an artifact due to the relatively low number of points).
The different galaxy schemes have been drawn on figure 15, versus the mass-ratio. The impacts of the parameters and (related to the thermal velocities) have not been explored.
Fig. 17:** Schematic grand design versus mass ratio** .
- Conclusion.
These results look interesting, but we have to be modest for several reasons. First of all we deal with 2d simulations, not 3d simulations. Strictly talking this does not describe the behaviour of mass points, located in a plane, imbeded in their own gravitational field, but the behaviour of "strings" interacting through gravitational (and anti-gravitational) forces. This comes from the form of the Poisson equation (36), which refers to a three dimensional medium. We just can hope that fully 3d simulations, applying to a flat system, with z-motions ,would provide similar results.
Suppose it would do. This model suggests a new mechanism which would drive the spiral structure of the galaxies. We find two regimes. First a dynamic friction slows down the central core. Then gravitational resonance process drives the system and arms forms, due to tidal effects. They do not dissipate by thermal effects, like in others works (the negative halo acts like a barrier and prevents their dissipation). These structures remain stable over an impressive number of turns (50). In fact, their origin is quite different. We find bars, stear-weels designs. It seems to be a promizing way to explore.
On another hand, this "2d galaxy" owns no gas. Basically, it is composed by 10,000 "stars" ou "groups of stars". The interaction with the second set of 10,000 objects (whose nature is not precised, except they own a negative
mass) provides a non-linear effect, a spiral pattern. If we could add some gas in this system, owing a positive mass (one order of magnitude lower than the mass of the "stellar material" : 10,000 positive mass objects), and whose elements would own a lower thermal velocity, this gas should rotate faster, in order to balance the gravitational force and to compensate the weakness its own pressure force effect. This gas should react to the non-homogeneous field, due to "set of stars" and enhance the spiral structure. If the velocity contrast between the gas and the stellar material would be large everywhere, this should produce spiral shock wave pattern, as observed. If such a program could be achieved, we could get a more realistic description of a galaxy.
References
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Achnowledgements :
This work is supported by the french CNRS and by the A. Dreyer Brevets et Développement company.
Déposé sous pli cacheté à l'Académie des Sciences de Paris, 1998.
Commentaires.
This work dates from 1994. It was only possible because Frédéric Landsheat, who was then a student at the German center for particle physics DAISY had access to a large system. It was entirely done in secret. When, having defended his thesis on data acquisition systems, he joined another center, this activity was interrupted. No additional work has been done since then and we have not succeeded in attracting French researchers, who have the appropriate computing means, to this research topic.
If a team, in France or abroad, wanted to resume these exploratory studies, we would be very happy. This work was submitted to many peer-reviewed publications, always accompanied by the film showing the birth of the barred galaxy, which was very suggestive. But none of them submitted it to a referee, contenting themselves with stereotypical answers like:
- Sorry, we don't publish speculative works.
This essay is just a very rough draft. A galaxy is far from being a system reducible to a single population of mass points. Moreover, the spiral structure phenomenon does not affect the entire galaxy, but mainly the interstellar gas, the population I being much less sensitive to the phenomenon. Therefore, simulations with two populations describing the galaxy itself would be necessary. It would also be necessary to represent the galaxy as it is, surrounded by ghost matter, if this model is valid, that is, surrounded by repulsive matter and relatively hot.
The parameters modulating the initial conditions are numerous. Ratio of average densities, agitation velocity in the two media, density profile in the galaxy, velocity profile. The transition to 3d poses the problem of the power of current systems, which is insufficient...