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Impacts of processes of star formation


A study on the Cat’s Paw Nebula provides new clues on the physical mechanisms that influence the processes of star formation. The observations, made with the Smithsonian’s Submillimeter Array, allowed astronomers not only to measure, for the first time, the magnetic fields in spatial regions of different sizes but to find the root cause which slows the birth of stars. The results were published in Nature.
A study of NGC 6334, better known as the Cat’s Paw Nebula and that is about 5,500 light-years away in the constellation Scorpio, has allowed us to analyze how magnetic fields affect the star formation of spatial regions of various sizes, ranging typically by several hundred light years up to a fraction of a light year. It is estimated that the amount of matter in the nebula is approximately 200 thousand solar masses and that it is gathering to form new stars, up to 30-40 times larger than the Sun’s.

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Credit: S. Willis (CfA); NASA/JPL-Caltech/SSC

The stars begin to form when the force of gravity acts on the material pulling inside huge clouds of gas and dust. However, gravity is the only force that comes into play during this process. In fact, a series of turbulent phenomena combined with the intense magnetic fields are opposed to the gravitational field perturbing the dynamics of the gas.
The researchers were able to measure the orientation of the magnetic fields within the nebula. “We found that the direction of the magnetic field is preserved on average over all regions that have different spatial dimensions, implying that the phenomena related to the turbulence in the cloud cannot be so significantly altering the direction of the magnetic field,” explains Hua-bai Li of The Chinese University of Hong Kong and lead author of the study, published in Nature, who led the observations at high resolution. “Although they are much weaker than the Earth, these cosmic magnetic fields have an important effect in regulating the processes of star formation,” adds TK Sridharan of the Center for Astrophysics (CfA) and co-author of the study.
Astronomers then analyzed polarized light due to dust within the nebula using various instruments including, in particular, the Smithsonian’s Submillimeter Array (SMA). “The unique ability of SMA, through which it was possible to measure the polarization with high angular resolution, allowed us to analyze the magnetic fields on smaller spatial scales,” says Ray Blundell, the CfA and director of SMA, which has not participated in the study. “SMA has really brought a big contribution in this field of research that continues with this work,” says the CfA Qizhou Zhang and co-author of the study.
Since the dust grains are aligned along the magnetic field, the researchers have exploited the issue of dust to determine the geometry of the magnetic field. The analysis of the data indicates that the magnetic fields tend to align in the same direction, even if the relative size of the spatial regions examined differs by a few orders of magnitude. The magnetic fields instead become misaligned only on smaller scales, namely in those cases in which they occur throughout a series of more chaotic dynamic processes following the star formation.
The most significant result that emerges from this work concerns the measure, for the first time, the magnetic fields in the spatial regions of various sizes present in an astrophysical object. When a molecular cloud collapses under the effect of gravity to form stars, the magnetic fields that impede the process becomes longer in temporal terms. As a consequence of this, only a fraction of the material contained in the cloud will be destined for the star formation while the rest will be dispersed in the space where it will remain available to give rise to new generations of stars.
Finally, according to the authors, the results of this work will have important implications for deriving other clues to the evolutionary history of our galaxy.

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