Primordial beryllium could reveal insights into the Big Bang

Some chemical elements appear much more abundantly in nature than others, which is partly due to how the elements originally formed. Scientists know that the light elements (hydrogen, deuterium, helium, and traces of lithium) were produced by fusion in the early Universe. Today, lithium, beryllium, and boron are constantly being produced in cosmic rays, while the heavier elements (up to iron) are formed by fusion in stars. Elements heavier than iron are formed by supernovae.

Physicists Maxim Pospelov of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, and the University of Victoria in Victoria, British Columbia, along with Josef Pradler, also of the Perimeter Institute, explain in a new study that investigating how chemical elements are produced can lead to a better understanding of what happened during the early Universe. The physicists have specifically investigated how beryllium could be used as a “Big Bang calorimeter” to probe the energy levels in the early Universe, and also to serve as a constraint on new physics models. Their study is published in a recent issue of Physical Review Letters.

In their analysis, Pospelov and Pradler have investigated what may have happened during Big Bang nucleosynthesis (BBN), a period that started about 3 minutes after the Big Bang and lasted for about 20 minutes. It was during this time that the first elements were produced, with the lightest elements in the greatest abundance. For instance, at that time only one lithium nucleus existed for every 10 billion hydrogen atoms. After BBN ended, the Universe became too cool to allow any further nuclear fusion reactions to take place.

Until now, researchers have thought that beryllium could not have been produced during rather generic circumstances in BBN. But here, Pospelov and Pradler have shown that, when an unknown particle X decays under the conditions during BBN, it can release a large amount of energy that can lead to the production of 9Be, which is the only stable isotope of beryllium. The formation of 9Be occurs at the end of a chain of transformations, going through a few light element isotopes including 6He, eventually leading to the beryllium isotope. When the physicists calculated the efficiency of this chain of transformations, they found that the process could produce a beryllium/hydrogen abundance ratio of 10-14 (or 1 gram of beryllium per 10 million tonnes of hydrogen).

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