Posted by: paulgarner | July 27, 2012

Where did all the lithium go?

This story is a few days old now, but I thought it was worth drawing attention to it all the same.

One of the great successes of the standard big bang model is its ability to predict the abundances of light elements observed in the universe. According to the standard model, the light elements (hydrogen, helium and lithium) were produced by nuclear fusion in the first few minutes of the big bang 13.7 billion years ago. And in the case of hydrogen and helium the predictions of the standard model appear to be confirmed to a high degree of accuracy.

But there has always been a problem with lithium: there simply doesn’t seem to be enough. In fact, observed lithium levels are three or four times lower than the standard model predicts. So the unresolved question is: where did all the primordial lithium go?

Now a study in the 13 July edition of Physical Review Letters complicates the matter further. Fabio Iocco of Stockholm University and Miguel Pato of the Technical University of Munich have found that microquasars – small black holes left behind by supernovae – may be a potential source of lithium. As matter spirals into the black hole, it approaches the speed of light and is heated up to 100 billion degrees Kelvin. Under such conditions, lithium can be produced by the collision of pairs of helium nuclei, and ejected out into space.

Iocco and Pato calculate that if such microquasars make up just one percent of the stellar-mass black holes in our galaxy, then this mechanism could have produced as much lithium as the big bang. Iocco adds a proviso: “We do not claim to know that microquasars necessarily have that kind of yield. But our provocative message is that physics could allow it.”

If confirmed, this finding would exacerbate the problem of the missing primordial lithium and may suggest that the standard model is in need of some modification.

Reference

Iocco F., Pato M. 2012. Lithium synthesis in microquasar accretion. Physical Review Letters 109:021102.

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