Evolutionary scenarios Three driving forces

Many neutron stars are thought to be born as isolated stars from isolated presupernovae (in neutron star community "isolated" is used for "solitary"). However, many other neutron stars are born in binary systems (also see § 1.4.6). Their evolution can be drastically different from the evolution of isolated stars (see, e.g., Lipunov 1992 and references therein). Let us assume that initially a binary contains two ordinary stars. Depending on their masses and orbital parameters, both companions undergo their nuclear evolution which can be strongly affected by mass exchange (accretion from one companion to the other, especially in compact binaries). Eventually, one of the companions may explode as a supernova producing a neutron star (or a black hole). The explosion may or may not destroy the binary. If survived, the binary continues its evolution and the second component may explode as a supernova (although there are other possibilities). If a compact double neutron star binary forms and survives, its evolution is accompanied by intense gravitational radiation (§ 9.1.2); the companions fall onto each other and finally merge producing apowerful outburst of gravitational, neutrino, and electromagnetic radiation.

In addition to accretion, the evolution of neutron stars can be strongly affected by their rotation and magnetic fields. Thus, the evolution and observational manifestations of neutron stars are regulated by the three main factors:

Rotation, Accretion, and Magnetic Field.

We will illustrate the effects of these factors in the next sections (also see Table 1.1). The effects are often superimposed. For instance, the magnetic field and rotation affect the regime of accretion on a neutron star and, hence, its X-ray emission (§ 1.4.6). On the other hand, an intense accretion can spin up the neutron star and affect its magnetic field. All in all, there are vastly different scenarios of neutron star evolution. Statistical studies of the evolution can be performed with population synthesis codes (see, e.g., Lipunov et al. 1996).

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