By Ron Cowen
The X-ray outburst of a young, sunlike star may provide new insights about planet formation. The X-ray study dates to last January, when amateur astronomer Jay McNeill of Paducah, Ky., used a small telescope to discover a cloud of dust and gas in the Milky Way’s Orion star-forming region. Other astronomers then found that a young sunlike star in the throes of a radiation-spewing tantrum had lit up the otherwise invisible cloud, dubbed McNeill’s nebula.
That’s when David A. Weintraub of Vanderbilt University in Nashville and his colleagues entered the picture. Using NASA’s Chandra X-ray Observatory, the astronomers found that the star, V1647 Orionis, was a bright X-ray source in early March 2004 but had faded by the end of the month. In the July 22 Nature, Weintraub and his collaborators propose an intriguing mechanism to explain both the X rays and the visible-light outburst. Many rotating stars, including the sun, spew X rays when magnetic fields rooted at their surface twist and snap. But this mechanism is insufficient to produce the searing temperatures of the gas Chandra observed at V1647 Orionis, the astronomers argue.
Instead, they propose that both the visible-light and the X-ray emissions were triggered by an avalanche of material falling from a protoplanetary disk—a thin doughnut of dust and gas surrounding the star. Planets may form from such a disk. A clash between the disk’s magnetic field and that of the star could have produced the X rays during the avalanche.
If the hypothesis is correct, astronomers might use X-ray observations to identify young stars that possess protoplanetary disks, Weintraub says.
