* Astronomy

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RE: Massive Stars

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Magnetic fields play important role in birth of massive stars

In a new research, astronomers have used the MERLIN radio telescope network centred on the Jodrell Bank Observatory to show that magnetic fields play an important role during the birth of massive stars.
Magnetic fields are already known to strongly influence the formation of lower-mass stars like our Sun.
This new study reveals that the way in which high-mass and low-mass stars form may be more similar than previously suspected.
Massive stars, more than 8 times the mass of the Sun, are crucial to the formation of other stars, planets and even life.
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Are the Largest Stars Born Like our Sun?

Explaining how the most massive stars are born, deep within their stellar nurseries, is one of the most persistent mysteries in modern astronomy. Now, observations at the Gemini Observatory provide convincing new evidence that these stellar heavyweights may be born in much the same manner as lightweights like our Sun.

"The problem is that when the most massive stars form it happens very quickly compared to stars like our Sun, and by the time they break free of their natal clouds they are already the finished article. If you want to see a massive star in the process of forming, you need to be able to see through the obscuring clouds to where the action is" - Ben Davies of the University of Leeds (UK) and the Rochester Institute of Technology.

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Image (481kb, 1528 x 1761)

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A massive star is born

A team of astronomers led by Lynn D. Matthews at the MIT Haystack Observatory has discovered a disk of gas swirling close to a young massive star, which they say offers the first evidence that massive stars form similarly to smaller stars. Because massive stars are believed to be responsible for creating most of the chemical elements in the universe that are critical for the formation of Earth-like planets and life, understanding how they form may help unravel mysteries about the origins of life.
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Image created from real data collected by Matthews' team showing the motions of gas clumps around Source I over the course of 22 months. The gas emission is color-coded according to the velocity of the material.
Credit Matthews et al.

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Making Massive Stars
Our understanding of star formation leans heavily on observations of stars like the sun, namely, those that are modest in mass and that are born and evolve at a relatively leisurely pace. By way of contrast, more massive stars mature so quickly that both observations and theory are hard pressed to follow their progress in detail. In the current theoretical description of star formation, a central protostar accretes material from a circumstellar disk that in turn is surrounded by a much larger, more nearly spherical envelope of infalling dust and gas. One result, a consequence of the star's spin, is that the young star produces polar jets of ionised gas and molecular outflows during its early stages of evolution. These outflows are widely seen, and are important markers of stellar youth. The issue for astronomers is whether this basic paradigm also applies to the formation of all stars, including massive stars, or whether there might be other processes at work.

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Massive Star Systems

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Massive stars

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Title: Accurate distances to nearby massive stars with the new reduction of the Hipparcos raw data
Authors: J. Maíz Apellániz, E. J. Alfaro, A. Sota

We use the new reduction of the Hipparcos data (van Leeuwen 2007) and a self-consistent distance determination technique for Lutz-Kelker limited samples to obtain distances to the massive stars in the solar vicinity. The distance uncertainties for the nearest massive stars have been substantially reduced with respect to those derived from the old Hipparcos reduction. In two cases (gamma2 Vel and theta2 Ori A) we have been able to verify that the new values are in good agreement with recent determinations with alternative methods. We also derive new values for the vertical displacement of the Sun with respect to the Galactic Plane and for the scale height of the thin disk from the spatial distribution of massive stars around us.

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Title: Massive Star Formation
Authors: Melvin G. Hoare, Jose Franco

This chapter reviews progress in the field of massive star formation. It focuses on evidence for accretion and current models that invoke high accretion rates. In particular it is noted that high accretion rates will cause the massive young stellar object to have a radius much larger than its eventual main sequence radius throughout much of the accretion phase. This results in low effective temperatures which may provide the explanation as to why luminous young stellar objects do not ionised their surroundings to form ultra-compact H II regions. The transition to the ultra-compact H II region phase would then be associated with the termination of the high accretion rate phase. Objects thought to be in a transition phase are discussed and diagnostic diagrams to distinguish between massive young stellar objects and ultra-compact H II regions in terms of line widths and radio luminosity are presented.

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