Nuclear astrophysics

It is an interdisciplinary part of both nuclear physics and astrophysics, involving close collaboration among researchers in various subfields of each of these fields.

This includes, notably, nuclear reactions and their rates as they occur in cosmic environments, and modeling of astrophysical objects where these nuclear reactions may occur, but also considerations of cosmic evolution of isotopic and elemental composition (often called chemical evolution).

Theories and simulations are essential parts herein, as cosmic nuclear reaction environments cannot be realized, but at best partially approximated by experiments.

In the 1940s, geologist Hans Suess speculated that the regularity that was observed in the abundances of elements may be related to structural properties of the atomic nucleus.

[3] Twenty years later, Bethe and von Weizsäcker independently derived the CN cycle,[4][5] the first known nuclear reaction that accomplishes this transmutation.

The interval between Eddington's proposal and derivation of the CN cycle can mainly be attributed to an incomplete understanding of nuclear structure.

Its lifetime as calculated from this assumption using the virial theorem, around 19 million years, was found inconsistent with the interpretation of geological records and the (then new) theory of biological evolution.

Alternatively, if the Sun consisted entirely of a fossil fuel like coal, considering the rate of its thermal energy emission, its lifetime would be merely four or five thousand years, clearly inconsistent with records of human civilization.

As matter is processed as such within stars and stellar explosions, some of the products are ejected from the nuclear-reaction site and end up in interstellar gas.

26Al has a lifetime of a million years, which is very short on a galactic timescale, proving that nucleosynthesis is an ongoing process within our Milky Way Galaxy in the current epoch.

Current descriptions of the cosmic evolution of elemental abundances are broadly consistent with those observed in the Solar System and galaxy.

Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common. The next three elements (Li, Be, B) are rare, intermediate-mass elements such as C, O, ..Si, Ca more abundant. Beyond Fe, there is a remarkable drop beyond Fe, heavier elements being 3-5 orders of magnitude less abundant. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance of elements according to whether they have even or odd atomic numbers, and (2) a general decrease in abundance, as elements become heavier. [ 11 ] Within this trend is a peak at abundances of iron and nickel and smaller peaks at elements whose beta-stable isotopes are located near neutron magic numbers .