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Starlight casts doubt on Big Bang details.

Examining the faint light from an elderly Milky way star, astronomers have detected a far greater abundance of beryllium atoms than the standard Big Bang model predicts. Three somewhat younger stars show a similar anomaly, according to unpublished data from the same team. While the findings do not contradict the premise that the expansion of the universe began with giant explosion, they do raise questions about certain assumptions of the standard model, such as the notion that the cosmos began as a perfectly smooth mixture.

These landmark beryllium assays -- previously considered all but impossible in such ancient stars -- demonstrate that "such measurements are indded possible, and [open] the way to a new investigation of the evolution of the early universe," the researchers write in the SEPT. 1 ASTROPHYSICAL JOURNAL.

Because the primordial universe did not contain heavy metals, the surfaces of old stars tend to have very low levels of iron. In ancient stars whose surface composition remains relatively unchanged from primordial times, any beryllium content should reflect levels characteristic of the universe soon after the Big Bang. For this reason, Gerard Gilmore of Cambridge University in England and his colleagues focused on a metal-poor star called HD 140283. This star has only one five-hundredth the iron abundance of the sun, indicating it formed some 15 billion years ago.

Using the Anglo-Australian Telescope in Coonabarabran, Australia, they measured the spectral intensity of two ultraviolet wavelengths characteristic of beryllium -- the fourth-lightest element -- emanating from the star's surface. Although the standard model holds that the primordial ratio of beryllium to hydrogen should be about [10.sup.-16] to 1, the researchers measured a value 1,000 times greater.

The team has not ruled out an alternative explanation for the unexpected abundance of beryllium: that cosmic rays striking the star sometime after the Big Bang might have generated extra beryllium. But if cosmic rays did boost beryllium levels, Gilmore says, they should have created 10 times more boron than beryllium. David Lambert of the University of Texas at Austin says mesaurements by the Hubble Space Telescope hint that HD 140283 does not contain enough boron to validate the cosmic ray scenario, but he says he cannot reject the hypothesis without further data.

If future findings favor a primordial explanation for the beryllium, scientists may have to modify some of their ideas about the Big Bang and its aftermath, says cosmologist David N. Schramm of the University of Chicago. The standard model assumes that the universe initially possessed a uniform density. But a large amount of primordial beryllium, he says, suggests the early universe was much lumpier than generally believed, with regins of high and low density. Schramm notes that neutrons migrating from high-density areas to low-density regions could have sparked a cascade of nuclear reactions that generated the extra beryllium.

Schramm emphasizes that a lumpy universe would still allow for expansion by a Big Bang-type explosion. The lumpiness might, however, offer insight into exactly how the four forces of nature became unified, while contrasting theories on how clusters of quarks formed protons and other particles collectively known as hadrons. Gilmore adds that a lumpy universe would contain significantly more ordinary, visible mass than a smooth universe.

Gilmore told SCIENCE NEWS he was heading back to Australia this week to obtain the beryllium spectra of a star with the lowest known metal abundance in the Milky Way. Studies of this star, he says, may further demonstrate beryllium's value in tracing the conditions of the early universe.
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Title Annotation:abundance of beryllium atoms
Author:Cowen, Ron
Publication:Science News
Date:Sep 7, 1991
Words:582
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