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VLA Transforms Field of Stellar Radio Astronomy

VLA Image of Betelgeuse

Though its designers did not expect it to detect stars, the VLA has produced major breakthroughs in our understanding of stellar physics. The VLA's sensitivity, its ability to observe at many frequencies in a short period of time, its high resolution, and its ability to make an image quickly make it the world's preferred instrument for radio studies of stars. Steven White, of the University of Maryland, wrote that "the VLA has completely transformed the field of stellar radio astronomy, and observations with the VLA are the foundation of virtually all advances in this field."

When the VLA began operating, some types of stars had been detected by radio telescopes. These included stars known to flare from time to time. However, no "ordinary" stars had been seen by a radio telescope. In a discovery that provided a major advance in scientists' understanding of stellar atmospheres, Dale Gary and Jeff Linsky, using the VLA, found that many ordinary stars have a feature lacked by the Sun -- an outer atmosphere, or corona, emitting brightly at radio wavelengths. The Sun's corona, on the other hand, emits only weakly at radio wavelengths. The radio emission in other stellar coronae is thought to be caused by the interaction of electrons with the star's magnetic field, rather than by any thermal process.

As the VLA proved itself capable of detecting more stars, astronomers sought to use it to study additional types, until today nearly every type of star has been studied with the VLA.

Stellar studies at the VLA have included nearly all types of stars in their "normal" lifetimes, from massive, hot stars to cool stars with only a fraction of the mass of the Sun. The VLA has revealed important details of double-star systems and their interactions, including regions in which material pouring out as part of one star's "stellar wind" is ionized by the high-energy radiation from its companion.

The addition, in the 1990s, of equipment allowing VLA observations at frequencies from 40-50 GHz opened up new opportunities for research on very young stars. Young stars are typically surrounded by dusty disks, and the new VLA observing frequencies allowed imaging of these disks. One important result showed a pair of young stars in a binary system, each of which was surrounded by a dusty disk. Since such dust disks are believed to be the material from which solar systems form, this observation indicated that binary-star systems, much more common in the Universe than single stars like the Sun, may indeed be capable of hosting pairs of planetary systems.

In 1998, high-frequency observations of Betelgeuse revealed convection cells in the atmosphere of this red supergiant star. This picture changed scientists' understanding of how the atmospheres of such stars work.

The VLA also has been used extensively to study the Sun. One early research result from the VLA, in 1980, indicated that the magnetic fields above a solar active region explosively reconnected just before a solar flare. The VLA is used routinely to study solar phenomena on very short time scales, often simultaneously with observations at other wavelengths by ground- and space-based instruments.

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