Abstract
The early evolution of the magnetic field and angular momentum of newly formed protostars are studied, using three-dimensional resistive MHD nested grid simulations. Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we calculate the cloud evolution from the molecular cloud core (nc ≃ 104 cm-3 and r = 4.6 × 105AU, where nc and r are the central density and radius, respectively) to the stellar core (nc ≃ 1022 cm-3;r ∼ 1 R⊙). The magnetic field strengths at the centers of clouds with the same initial angular momentum but different magnetic field strengths converge to a certain value as the clouds collapse for nc ≲ 1012 cm-3. For 1012 cm-3 ≲ nc ≲ 1016 cm-3, ohmic dissipation largely removes the magnetic field from a collapsing cloud core, and the magnetic field lines, which are strongly twisted for nc ≲ 1012 cm-3, are decollimated. The magnetic field lines are twisted and amplified again for nc ≳ 1016 cm-3, because the magnetic field is recoupled with warm gas. Finally, protostars at their formation epoch (nc ≃ 1021 cm-3) have magnetic fields of ∼0.1 -1 kG, which is comparable to observations. The magnetic field strength of a protostar depends slightly on the angular momentum of the host cloud. A protostar formed from a slowly rotating cloud core has a stronger magnetic field. The evolution of the angular momentum is closely related to the evolution of the magnetic field. The angular momentum in a collapsing cloud is removed by magnetic effects such as magnetic braking, outflow, and jets. The formed protostars have rotation periods of 0.1-2 days at their formation epoch, which is slightly shorter than observations. This indicates that a further removal mechanism for the angular momentum, such as interactions between the protostar and the disk, wind, or jets, is important in the further evolution of protostars.
| Original language | English |
|---|---|
| Pages (from-to) | 1198-1213 |
| Number of pages | 16 |
| Journal | Astrophysical Journal |
| Volume | 670 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - Dec 1 2007 |
| Externally published | Yes |
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All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
Cite this
Magnetic fields and rotations of protostars. / Machida, Masahiro N.; Inutsuka, Shu Ichiro; Matsumoto, Tomoaki.
In: Astrophysical Journal, Vol. 670, No. 2, 01.12.2007, p. 1198-1213.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Magnetic fields and rotations of protostars
AU - Machida, Masahiro N.
AU - Inutsuka, Shu Ichiro
AU - Matsumoto, Tomoaki
PY - 2007/12/1
Y1 - 2007/12/1
N2 - The early evolution of the magnetic field and angular momentum of newly formed protostars are studied, using three-dimensional resistive MHD nested grid simulations. Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we calculate the cloud evolution from the molecular cloud core (nc ≃ 104 cm-3 and r = 4.6 × 105AU, where nc and r are the central density and radius, respectively) to the stellar core (nc ≃ 1022 cm-3;r ∼ 1 R⊙). The magnetic field strengths at the centers of clouds with the same initial angular momentum but different magnetic field strengths converge to a certain value as the clouds collapse for nc ≲ 1012 cm-3. For 1012 cm-3 ≲ nc ≲ 1016 cm-3, ohmic dissipation largely removes the magnetic field from a collapsing cloud core, and the magnetic field lines, which are strongly twisted for nc ≲ 1012 cm-3, are decollimated. The magnetic field lines are twisted and amplified again for nc ≳ 1016 cm-3, because the magnetic field is recoupled with warm gas. Finally, protostars at their formation epoch (nc ≃ 1021 cm-3) have magnetic fields of ∼0.1 -1 kG, which is comparable to observations. The magnetic field strength of a protostar depends slightly on the angular momentum of the host cloud. A protostar formed from a slowly rotating cloud core has a stronger magnetic field. The evolution of the angular momentum is closely related to the evolution of the magnetic field. The angular momentum in a collapsing cloud is removed by magnetic effects such as magnetic braking, outflow, and jets. The formed protostars have rotation periods of 0.1-2 days at their formation epoch, which is slightly shorter than observations. This indicates that a further removal mechanism for the angular momentum, such as interactions between the protostar and the disk, wind, or jets, is important in the further evolution of protostars.
AB - The early evolution of the magnetic field and angular momentum of newly formed protostars are studied, using three-dimensional resistive MHD nested grid simulations. Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we calculate the cloud evolution from the molecular cloud core (nc ≃ 104 cm-3 and r = 4.6 × 105AU, where nc and r are the central density and radius, respectively) to the stellar core (nc ≃ 1022 cm-3;r ∼ 1 R⊙). The magnetic field strengths at the centers of clouds with the same initial angular momentum but different magnetic field strengths converge to a certain value as the clouds collapse for nc ≲ 1012 cm-3. For 1012 cm-3 ≲ nc ≲ 1016 cm-3, ohmic dissipation largely removes the magnetic field from a collapsing cloud core, and the magnetic field lines, which are strongly twisted for nc ≲ 1012 cm-3, are decollimated. The magnetic field lines are twisted and amplified again for nc ≳ 1016 cm-3, because the magnetic field is recoupled with warm gas. Finally, protostars at their formation epoch (nc ≃ 1021 cm-3) have magnetic fields of ∼0.1 -1 kG, which is comparable to observations. The magnetic field strength of a protostar depends slightly on the angular momentum of the host cloud. A protostar formed from a slowly rotating cloud core has a stronger magnetic field. The evolution of the angular momentum is closely related to the evolution of the magnetic field. The angular momentum in a collapsing cloud is removed by magnetic effects such as magnetic braking, outflow, and jets. The formed protostars have rotation periods of 0.1-2 days at their formation epoch, which is slightly shorter than observations. This indicates that a further removal mechanism for the angular momentum, such as interactions between the protostar and the disk, wind, or jets, is important in the further evolution of protostars.
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U2 - 10.1086/521779
DO - 10.1086/521779
M3 - Article
AN - SCOPUS:40249094422
VL - 670
SP - 1198
EP - 1213
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
ER -