| 12 | | If they’re only marginally magnetically critical, they will have a tendency to collapse along field lines rather than across them. This will result in an increase of the density in the collapsing cloud, while not effecting the field strength. (i.e., were collapse perpendicular to the field lines, drag between the field and collapsing gas would cause the field to get pulled in with the gas/distorted -- increasing its strength). Zeeman measurements support this concept -- showing that up until ~ 10^3 cm^(-3), field strength is measured as constant, but above that density, the field grows with density -- indicating collapse perpendicular to the field. So first the cloud collapses along field lines (making sheets), and then once the self-gravity wins out, it will begin collapsing radially within the sheets (forming filaments). |
| | 12 | For marginally magnetically critical clouds, collapse first occurs along field lines rather than across them, as there is no magnetic support in that direction. This results in an increase in density without a concomitant change in field strength (were collapse occurring perpendicular to the field lines, drag between charged particles and field would cause field distortion, increasing its strength). Zeeman measurements support this concept -- showing that up until ~ 10^3^ cm^-3^, field strength is constant. Above that density, the field grows with density -- indicating collapse perpendicular to the field. This type of collapse can lead to sheets, filaments, and knots, depending on the degree of initial anisotropy in the mass distribution. As an example, you can imagine a cloud collapsing along field lines will make sheets, and then once the self-gravity wins out, it will begin collapsing radially within the sheets, forming filaments. |
