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凑合着了解一下吧。
Astronomic observations with the latest and greatest telescopes are leading astronomers to embrace the idea
that stars usually form in clusters, even if they end up, like our Sun, isolated from other stars. Cosmochemists
using optical microscopes, electron microscopes, and mass spectrometers are finding evidence supporting the
idea, along with important details about the star-forming regions and about the earliest history of the Solar
System. The latest breakthrough is reported by Martin Bizzarro and his colleagues at the Geological Institute
and Geological Museum in Denmark, at the University of Texas, and at Clemson University in South Carolina.
They made high-precision measurements of iron and nickel isotopes. The results show that the oldest
planetesimals to form in the solar system did not contain any iron-60 ( 60Fe), which decays to nickel-60 ( 60Ni)
with a half-life of only 1.5 million years, yet somewhat younger materials did contain it. In contrast,
aluminum-26 ( 26Al), with a half-life of 740,000 years, was relatively uniformly distributed.
The 60Fe cannot have come from a source too far from the infant Sun. If too far away it would decay before
arriving or be so diluted that we could not measure it. The exploding star had to be in the Sun's general vicinity.
It was a cluster mate of the Sun.
One type of massive star is called a Wolf-Rayet star (named after the discoverers). In these large objects,
elements formed inside by nuclear fusion, such as oxygen and aluminum, migrate toward the surface. This
concentration of material begins to adsorb light from inside, eventually resulting in strong winds blowing off the
surface and into interstellar space. The winds are shown in the image, below, taken in the infrared. Astronomers
believe that most massive stars (those >20 times the mass of the Sun) go through a Wolf-Rayet phase, which
ends when they explode as supernova. |
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发表于 2011-10-2 23:14:47
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