Magnetism fights starbirth

via Astronomy Now.

We are used to hearing about stars being the fight of fusion generated heat inspired expansion against gravitationally induced collapse. Either the star shines too brightly (over the Eddington limit) and blows itself apart or, more often, the fuel runs out and the star collapses, with the outer layers bouncing off the core and producing a nebula. Well it seems a similar battle is fought within the heart of ‘molecular clouds’, giant clouds of gas and dust in which stars are born.

Within these clouds, knots of high density material act as cores to which other gas and dust can gravitate and slowly collapse in, forming a protostar over time. However, such gravitational collapse is fought by two processes, turbulence, which swirls the material, forming an outward force, and magnetism, which pulls ionic material away along its field lines. There has been some controversy over which was the most significant factor in slowing down collapse.

Now a team led by Harvard-Smithsonian Center for Astrophysics astronomer Hua-bai Li has begun studying the question. Magnetism in twenty-five cores within 6,500 light years of Earth was studied by looking on its effect on the polarisation of light. This showed that magnetic fields connecting different cores retained their original directions. They hadn’t been messed up by turbulent flows, suggesting magnetism was the dominant dissenting voice in these areas of gravitational collapse.

Still, no wonder stars go in such spectacular fashion. Gravity comes along, finds a pocket of gas, tries to collapse it, byt magnetism sucks away some material. When it gets somewhere, the actual energy of accelerating this gas into one packet makes it heat up and expand again. The heat and density then lead to fusion, which also expands the star and fights gravity. Hydrogen burning gives way to helium, CNO and all kinds of other burning until eventually the star gives way and gravity gets its white dwarf, neutron star or maybe even black hole…


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