Origin of the heavier elements

Since Big Bang Theoryplugin-autotooltip__plain plugin-autotooltip_bigBig Bang theory

There is now a large body of evidence (from different sources) to support the Big Bang Theory for the origin of the universe, but the problem remains as to the origin of the material or energy which initialised it.

As the UK’s Astronomer Royal Martin Rees has put it : doesn't provide an explanation for the origin of the heavier elements which make up most of the Earth and the life on it, many cosmological theorists contend that they may have instead formed in supernovae explosions.

Exact mechanism(s) however, to explain the production of many of the elements heavier than iron (so called trans-ferric elements) have still not been agreed.

"It’s one of the classic unsolved problems of physics." ( quote from New Scientist 4 Feb 2006 ) ^{unable to find reference or link}

A fundamental challenge in Nuclear Astrophysics is the understanding of the formation of trans-ferric elements. The site for the production of many of the elements heavier than iron, including gold, platinum and uranium is still unknown."

Source Prof. Sydney Gales at GANIL accelerator facility, France

The 'r-process'- the proposed mechanism by which rapid neutron capture occurs in collapsing supernovae to create about half of the heavy elements above iron - is 'still experiencing major problems' (as at 2011)

See: What are the astrophysical sites for the rr-process and the production of heavy elements? Progress in Particle and Nuclear Physics, Volume 66, Issue 2, April 2011, Pages 346-353.

And a 2016 paper presented at The 13th International Symposium on Origin of Matter and Evolution of Galaxies underlined the uncertainties :

Astrophysical site(s) of rapid neutron-capture process (r-process) is (are) not identified yet. Although core-collapse supernovae have been regarded as one of the possible candidates of the astrophysical site of r-process, nucleosynthesis studies suggest serious difficulties in core-collapse supernovae to produce heavy elements with mass number of ≳110." [i.e Zircon]

Update 2017

If the following results are confirmed, the mystery of heavy element formation may have been solved.

New observations which link gamma-ray emissions to gravitational-wave events logged by LIGO (which has detected a merger of two Neutron stars) are said to show an electromagnetic 'signature' that is compatible with calculations about heavy element formation.

The implication is that the elements did not form in supernovae explosions, but instead in mergers of neutron stars

“People have long suspected that heavy elements were made in neutron star mergers, but this is really the first time we’ve nailed that down,” says Andrew Levan at the University of Warwick, UK. This merger made something like the mass of the Earth in gold, he says, along with other heavy elements such as platinum, lead and uranium."

See: New Scientist, Oct 2017

More coverage of the story here in the journal Nature

These results offer a new possibility for clarifying six decades of uncertainty over the site of origin of r-process nuclei.

Source : Wikipedia

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