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New star forming from interstellar cloud.

In 1,000,000 years or so, a new star will over the Earth in the general direction of the constellation sagittarius, predicts an international team of astrophysicists. "We've believed for a long time that stars form clouds in interstellar space when gravity causes the clouds to collapse," explains Neal Evans of The University of Texas at Austin Astronomy Department. "However, we've had a hard time seeing the signature of a collapse."

Evans and his associates, Shudong Zhou of the University of Illinois and Carsten Kompe and C.M. Walmsley of the Max Planck Institute for Radioastronomy, Bonn, Germany, have found the signature of collapse by measuring the velocity of gases in the could, which is one-and-a half light years in diameter. They have discovered that the gases on the near side of the cloud, while those on the far side are hunting toward it at a comparable velocity. This demonstrates that the entire cloud is collapsing toward its center.

The cloud, known as B335, was discovered early in the century by the American astronomer Edward Emerson Barnard. It is invisible to the eye, appearing only as a black, starless area through a telescope. This is because the molecules do not possess enough energy to radiate at wavelengths visible to the eye, yet the dust in the cloud blots out the light of stars behind it.

The cloud is "visible" at infrared and radio wavelengths, and it is at both of those wavelengths that the astronomers have accumulated their data. The radio waves generated by the molecules colliding in the cloud are particularly important because such waves freely pass through the dust and can be analyzed with ground-based radio telescopes. The infrared radiation given off by the cloud is not important in determining whether the gases are in motion, Evans explains, but nonetheless is crucial to determine that the cloud is giving off more energy than it is absorbing from other stars.

Determining that the gases are moving is a feat accomplished though knowledge of the behavior of light, Evans points out. Light and other types of electromagnetic radiation such as radio waves and infrared always travel at the same velocity, regardless of the motion of the source and the observer, as Einstein's Theory of Special Relativity demonstrates. However, the wavelength of the radiation varies by precise amounts if either the source of the radiation or the observer is moving along the direction the waves are travelling.

In fact, individual particles of electromagnetic radiation - or photons - behave in much the same way as an ambulance siren that seems to lower in pitch after passing by. To an observer on Earth, photons appear to be "higher," or of shorter wavelengths and higher frequency if they are coming from a source that is travelling toward Earth, and "lower" if they emanate from a source that is moving away. This phenomenon, known as the Doppler effect, allows astrophysicists to measure the velocity of an object by the minute shifts in the wavelength of the incoming radiation.

Since wavelengths can be determined to extremely small tolerances, it would seem that astronomers should have detected a star in the process of formation long ago. Such is not the case. "What makes the search for signatures of star formation so difficult is that clouds of this sort show evidence of outflow," he says.

At present, the best guess for the cause of the particle outflows is related to the conservation laws, Evans notes - in this case, the conservation of angular momentum. Because the matter falling in wards tends to spin faster, astrophysicists think that a newly forming star propably will sling off some of its mass. For the same reason, pirouetting ice skaters are able to slow down their rate of spin by thrusting their arms outward. "So in the past, even when we thought that a cloud was collapsing, we would still see evidence of molecules flowing outward, and this made it impossible to demonstrate that the matter was collapsing due to the effect of gravity."
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Publication:USA Today (Magazine)
Date:Jun 1, 1993
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