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News Release 157 of 250

July 12, 2001 09:00 AM (EDT)

News Release Number: STScI-2001-19

Magnetic Fields Weave Rings Around Stars

July 12, 2001: There are stars with planets. Stars with companion stars. Stars with pancake-shaped disks of rocky debris. But how about young, hot, hefty stars embedded in large inner tube-shaped clouds of shimmering gas? Astronomers had suspected that the thick rings are the signatures of stars with strong magnetic fields. Sometimes, the surfaces of those "magnetic stars" possess peculiar chemical compositions, namely low amounts of "heavy elements" like iron. Now a team of astronomers analyzing archival information on four stars provides convincing evidence of the link between rings and magnetic fields. The team also suggests that rings around massive stars are more common than scientists thought. The study shows that magnetic stars with normal chemical abundances can have rings, too.

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Q & A: Understanding the Discovery

  1. 1. How does a magnetic field form a ring?

  2. According to a popular theory, the magnetic field directs the flow of particles streaming off the star in the form of "stellar winds" — streams of charged particles that travel about 2 million miles per hour (4 million kilometers per hour). All hot stars have stellar winds, but those without strong magnetic fields release streams of particles in all directions. A star with a magnetic field positioned along the poles — like the ones in this study — channels the wind only from the two poles. The wind particles, especially material like iron, are driven by the star's intense radiation and travel on the cloverleaf track over the star. A few hours later, they slam into streams of matter traveling from the opposite direction, somewhere along the star's tilted magnetic equator.

    The collisions resemble a series of head-on car accidents along a congested highway. As the particles slam into each other, they stop and congregate along the equator, eventually forming a thick ring. The particle collisions also cause the material to glow and radiate at high energies, detected in ultraviolet and perhaps X-ray wavelengths.

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Animation Still: Greg Bacon (STScI/AVL)

Science Credit: NASA, Myron Smith (STScI), and Detlef Groote (University of Hamburg)