Stars in the dust

From San Diego, at a meeting of the American Astronomical Society

New observations of one of the sun’s brightest neighboring stars show that the debris disk surrounding it contains much fine dust, probably from recent collisions between massive objects near the star.

Using the orbiting Spitzer Infrared Observatory, Kate Y.L. Su of the University of Arizona in Tucson and her colleagues found evidence for huge amounts of microscopic dust around the star, named Vega. Because radiation from any star such as Vega quickly clears away such particles, Su’s team concludes that the dust must have been produced by recent collisions. In particular, the researchers propose that two or more Pluto-size objects collided sometime in the past million years and that many subsequent collisions between the resulting fragments led to the disk around Vega.

Two other teams using ground-based telescopes—one group led by Benjamin M. Zuckerman of the University of California, Los Angeles and the other by Charles M. Telesco of the University of Florida in Gainesville—have found signs of similar collisions around other Milky Way stars.

Zuckerman’s team reports that a 400-kilometer-wide object appears to have been converted into dust around the star HIP8920 sometime in the past several thousand years. Telesco and his colleagues gathered data from the star Beta Pictoris indicating that 100-km-wide objects collided there within the past 100 years.

Astronomers have long assumed that much of the dust in debris disks around stars comes from ongoing collisions between objects the size of small asteroids, but the new findings are the first to show evidence of recent collisions involving far more-massive objects.

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