Mon 20 Feb 2017
From (The Plasma Universe Wikipedia-like Encyclopedia)
- According to the conventional view, star formation is due to a Jeans collapse of a massive interstellar cloud. The difficulty associated with a cloud of less than 100-10 000 M⊙ have led to the invention of complicated mechanisms which are supposed to fragment the collapsing cloud. So far no convincing arguments have been presented for a star formation in this way. Among other difficulties it does not lead to the formation of a planetary system around the newborn star without a number of ad hoc assumptions. The real argument for spending so much work on the Jeans collapse seems to have been that no other mechanism has been seriously suggested.
- As an alternative to these views we shall here try a new approach based on the following three principles.
- Cosmic plasma physics should not be based on an obsolete formalism but on what is known about the properties of a plasma from laboratory experiments and in situ space measurements.
- Interstellar clouds are not necessarily contracted and kept together by gravitation. Magnetic fields of the type which is observed in the magnetosphere and heliosphere are likely to exist also in interstellar space. In the same way as in our neighbourhood, they will collect gas and compress it. In this way gas clouds of any size may be formed, even so small that self-gravitation cannot keep them together. As we have found in Part II, the electric currents necessary for such pinching are not excessive. In fact they are reasonable extrapolations from currents which have been measured in the heliosphere.
- Even if not kept together by gravitation, a cloud of dusty plasma is gravitationally unstable in the sense that dust is collecting at the centre of gravity. A dust ball is formed, which by its gravitation speeds up the sedimentation of dust, and – in a later phase – also accretes gas from its surroundings.
- The usual conclusion that magnetic fields necessarily counteract the collapse of an interstellar cloud is model dependent. In other, and at least equally reasonable magnetic field models, the magnetic field compresses the cloud. It is possible that dark clouds are formed and kept together by electromagnetic effects.
- In a dusty cloud gravitation collects the dust at the centre of gravity of the cloud. A dust ball is formed which, when it has grown large enough, collects gas from its surrounding. This process leads to the formation of a star.
- In a cloud with irregular structure a number of such dust balls may be formed which later join by a process which is similar to the 'planetesimal' formation of planets and satellites around the Sun. Such a `stellesimal' accretion may result in a body having the same mass and angular momentum as the primeval Sun.
- Both (2) and (3) result in a state around the star which is reconcilable with the state which an analysis of solar system data indicates to be a likely primeval state for planetary formation."
- Anthony L. Peratt, "Evolution of the Plasma Universe: II. The Formation of Systems of Galaxies" in IEEE Transactions on Plasma Science Vol. PS-14 No.6. See VIII. Alfvén-Carlqvist Model for Star Formation in Pinched Filaments. (Dec 1986) (Full text)
- Hannes Alfvén and Per Carlqvist, "Interstellar clouds and the formation of stars" in Astrophysics and Space Science, vol. 55, no. 2, May 1978, p. 487-509.