X-Ray Study on the Evolution and Structure of Protostars

Abstract

Protostars, the first stage of stellar evolution, are born in a dense core of a molecular cloud with temperature of about 10 K. X-rays can be emitted from a high temperature plasma of 10⁶-10⁸K, hence may not be expected from protostars. Nature, however, is much more imaginative than we are. The Japanese X-ray satellite ASCA found X-rays from a few protostars. The US satellite Chandra successively found that X-rays are common in most of the young stars. Many protostars show flare-like events similar to our sun, hence the X-rays are attributable to solar type magnetic activities. The X-ray work should finally lead to our deep understanding of the evolution and structure of young stars and planets. This paper overviews the pioneering results in the unique waveband, the X-ray.