Credit: K. Koyama (Kyoto U), Y. Tsuboi (Penn State)/NASA/CXC

The YSO Christmas Tree

Young stellar objects (YSOs) are newborn stars which are just forming out of massive clouds of gas and dust which are distributed throughout the Galaxy. A single cloud can form dozens or hundreds of stars, so that most young stars are found in groups. Like young children, these young stars are extremely active. This activity shows up clearly in X-rays. The X-ray emission from YSOs tends to be very erratic, probably due to the occurence of stellar type flares, like the more familiar flares which occur on the Sun, but many times more powerful. Now the Chandra X-ray observatory's ACIS camera has provided astronomers with the best view of this extraordinary activity. The image above shows a Chandra ACIS image of an enormous stellar nursery, a giant cloud of gas and dust in the constellation of Ophiuchus. The bright points in the image are X-ray emitting stars (the red stars suffer less absorption from the cloud and presumably are on the near side of the cloud, while the blue stars are more absorbed and presumably buried deeper in the cloud). Because ACIS measures the time of arrival of each X-ray photon it detects, astronomers can use the ACIS data to measure the brightness of the X-ray source with time. The graphs attached to each X-ray star shows the variation of the stellar X-ray brightness. The rise in each graph indicates a time when the star was undergoing an increase in X-ray brightness due to a stellar flare. Thus, in a time-lapsed X-ray movie of this molecular cloud, the stars blink on and off like lights on a Christmas tree.

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Page Author: Dr. Michael F. Corcoran
Last modified December 11, 2000