Self-similar fragmentation regulated by magnetic fields in a region forming massive stars

Li, Hua-bai; Yuen, Ka Ho; Otto, Frank; Leung, Po Kin; Sridharan, T. K.; Zhang, Qizhou; Liu, Hauyu Baobab; Tang, Ya-Wen; Qiu, Keping

doi:10.1038/nature14291

Cited by 115 publications

(151 citation statements)

References 43 publications

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“…More intriguingly, it is the one aligned with the B-field that holds the higher SFR. Together with another observed piece of evidence that Galactic B-field direction anchors deeply into cloud cores 12 and thus plays a role in cloud fragmentation 13 , we were prompted to survey whether the cloud-field alignment has a connection with SFR.…”

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confidence: 99%

The link between magnetic field orientations and star formation rates

Li¹,

Jiang²,

Fan³

et al. 2017

Nat Astron

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Understanding star formation rates (SFR) is a central goal of modern star-formation models, which mainly involve gravity, turbulence and, in some cases, magnetic fields (Bfields) 1,2 . However, a connection between B-fields and SFR has never been observed. Here, a comparison between the surveys of SFR 3,4 and a study of cloud-field alignment 5 -which revealed a bimodal (parallel or perpendicular) alignment-shows consistently lower SFR per solar mass for clouds almost perpendicular to the B-fields. This is evidence of B-fields being a primary regulator of SFR. The perpendicular alignment possesses a significantly higher magnetic flux than the parallel alignment and thus a stronger support of the gas against selfgravity. This results in overall lower masses of the fragmented components, which are in agreement with the lower SFR.It is not difficult to imagine that the SFR of a molecular cloud should be related to the mass of gas it contains, due to self-gravity. On the whole, this trend has indeed been observed 3,4 . On the other hand, star formation efficiencies of molecular clouds are usually just a few percent 6 while cloud ages are at least comparable to their free-fall time (~Myr) 7 . This requires other forces to slow down gravitational contraction 8 . In addition, clouds with a similar mass and age can have different SFR; for example, it is well known that the Ophiuchus cloud has a significantly higher SFR than its neighbour, the Pipe Nebula 3,4 . In Figure 1, we can see a significant difference between the two dark clouds: Ophiuchus is accompanied by the colourful nebulae, which is a signature of active stellar feedback, while Pipe looks very quiescent in comparison. No one knows the reason for these differences in SFR. Another good example is the pair of Rosette and G216-2.5 molecular clouds 9 , where turbulence had been suspected as the cause of their very different SFRs. But later their turbulent velocity spectra were found almost identical 9 . Recently, a good agreement has been discovered between the empirical column density threshold for cloud contraction and the magnetic critical column density of the Galactic field (~10 µG) 5,10 . For densities lower than this threshold, the field strength is independent of densities 11 ; i.e., gas must accumulate along field lines. Also, a bimodal cloud-field alignment, which is another signature of field-regulated (sub-Alfvenic turbulence) cloud formation, was recently observed in the Gould Belt 5 , where, interestingly, Pipe and Ophiuchus (Figure 1) are aligned differently from their local fields. More intriguingly, it is the one aligned with the B-field that holds the higher SFR. Together with another observed piece of evidence that Galactic B-field direction anchors deeply into cloud cores 12 and thus plays a role in cloud fragmentation 13 , we were prompted to survey whether the cloud-field alignment has a connection with SFR.Luckily, both the cloud-field alignment 5 and SFR 3,4 of the Gould Belt clouds have been very well studied (Table 1). Both Heiderman e...

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confidence: 99%

The link between magnetic field orientations and star formation rates

Li¹,

Jiang²,

Fan³

et al. 2017

Nat Astron

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“…;Schneider et al 2012;Liu et al 2012;Peretto et al 2013). Massive dense cores are magnetized with magnetic field strengths of 0.1-1 mG (Falgarone et al 2008;Girart et al 2013;Qiu et al 2013;Frau et al 2014;Li et al 2015;Houde et al 2016). Since the star-formation rate in dense gas is only few percents of the rate of a free-fall collapse, magnetic fields are suggested to be an important ingredient supporting massive dense cores against self-gravity (Krumholz & Tan 2007).…”

Section: Introductionmentioning

confidence: 99%

“…For massive dense cores with typical sizes of 0.1 pc and distances of few kiloparsecs, several interferometric observations have been performed to spatially resolve the magnetic field structures (Rao et al 1998;Lai et al 2001Lai et al , 2002Lai et al , 2003Cortes et al 2008Cortes et al , 2016Girart et al 2009Girart et al , 2013Tang et al 2009aTang et al ,b, 2010Tang et al , 2013Liu et al 2013;Qiu et al 2013Qiu et al , 2014Hull et al 2014;Frau et al 2014;Sridharan et al 2014;Li et al 2015, also see Zhang et al 2014 for a review of SMA polarization legacy project). The observations reveal diverse magnetic field structures from ordered hour-glass shapes (e.g.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Fields in the Massive Dense Cores of the DR21 Filament: Weakly Magnetized Cores in a Strongly Magnetized Filament

Ching

Lai

Zhang

et al. 2017

ApJ

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We present Submillimeter Array 880 µm dust polarization observations of six massive dense cores in the DR21 filament. The dust polarization shows complex magnetic field structures in the massive dense cores with sizes of 0.1 pc, in contrast to the ordered magnetic fields of the parsec-scale filament. The major axes of the massive dense cores appear to be aligned either parallel or perpendicular to the magnetic fields of the filament, indicating that the parsec-scale magnetic fields play an important role in the formation of the massive dense cores. However, the correlation between the major axes of the cores and the magnetic fields of the cores is less significant, suggesting that during the core formation, the magnetic fields below 0.1 pc scales become less important than the magnetic fields above 0.1 pc scales in supporting a core against gravity. Our analysis of the angular dispersion functions of the observed polarization segments yields the plane-of-sky magnetic field strengths of 0.4-1.7 mG of the massive dense cores. We estimate the kinematic, magnetic, and gravitational virial parameters of the filament and the cores. The virial parameters show that in the filament, the gravitational energy is dominant over magnetic and kinematic energies, while in the cores, the kinematic energy is dominant. Our work suggests that although magnetic fields may play an important role in a collapsing filament, the kinematics arising from gravitational collapse must become more important than magnetic fields during the evolution from filaments to massive dense cores.

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“…We note, however, that these values of ambipolar diffusion times rely on the idealized power-law relationships between r m , B 0 , and n H , whose accuracy may be disputed (Draine 2011). For example, recent work of Tritsis et al (2015) suggests that for lowerdensity, nonspherical clouds, B 0 might be better written as proportional to n n 0.5 , and Li et al (2015) suggest n n 0.4 in NGC 6334.…”

Section: A Simple Model For the Timescale For Ambipolar Diffusion In mentioning

confidence: 99%

“…There have been extensive observations of molecular clouds, which relate their size, contained mass, and magnetic fields through power-law relationships with number density (Crutcher et al 2010;Draine 2011;Crutcher 2012;Roy et al 2014;Li et al 2015;Tritsis et al 2015). Relationships given in Draine (2011) andCrutcher et al (2010) yield the general result that for low-mass, cold, quiescent prestellar cores, the ratio of mass to magnetic flux is less than the critical value, that is, cores are in general magnetically subcritical.…”

Section: Introductionmentioning

confidence: 99%

Enabling Star Formation via Spontaneous Molecular Dipole Orientation in Icy Solids

Rosu-Finsen

Lasne

Cassidy

et al. 2016

ApJ

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It is shown here how new experimental data, for the electrical properties of solid CO, can be used to fill important gaps in our understanding of the evolution of prestellar cores. Dust grains with a mantle of CO lead to a reduction in the degree of ionization in these cores by a factor of between 5 and 6. The lifetimes for expulsion of magnetic fields from cores, a process generally necessary for gravitational collapse, are reduced from current estimates of several megayears, by a similar factor. This removes a major inconsistency, since lifetimes now tally with typical ages of prestellar cores of a few hundred thousand to 10 6 yr, derived from observations. With the reduced timescales, cores also escape disruption by Galactic supernova remnants. Our results provide a natural mechanism for the generation of so-called magnetically supercritical cores, in which the magnetic field alone cannot prevent gravitational collapse. In addition, we find a minimum value for the density of prestellar cores of (1.1±0.1) ×10 4 H 2 cm −3 , in agreement with observations.

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Self-similar fragmentation regulated by magnetic fields in a region forming massive stars

Cited by 115 publications

References 43 publications

The link between magnetic field orientations and star formation rates

The link between magnetic field orientations and star formation rates

Magnetic Fields in the Massive Dense Cores of the DR21 Filament: Weakly Magnetized Cores in a Strongly Magnetized Filament

Enabling Star Formation via Spontaneous Molecular Dipole Orientation in Icy Solids

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