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in Binary Systems Up: Ejectors
in Massive Binary Previous: The
Number of Ejectors
In the very first years after the discovery of radiopulsars, it became clear that for some reason they avoid forming binary systems. Three hypotheses were put forward to explain such a strange incompatibility.
Suppose that a normal star loses matter in a spherically symmetric way. In this case, the optical thickness associated with the free-free absorption in the stellar wind is
where
K is the temperature of the stellar wind,
cm is the wavelength of the radiofrequency radiation, and a
is the semi-major axis of the orbit expressed in units of solar radii.
In massive binary systems with
, we have
. Hence the stellar wind is opaque even for very wide systems (
).
Which of the above three mechanisms is responsible for the deficit of radiopulsars in binary systems with normal stars? To answer this question correctly, a more detailed analysis of the evolution of normal and neutron stars in binary system is needed. Recent studies (see Lipunov et al., 1995d and Section 7 for more detail) suggest that the ill-defined conditions of stellar wind transparency turn out to be of a rather small significance since after the first supernova explosion the distribution of binaries by optical thickness of the wind is fairly flat on a logarithmic scale (which reflects the initial flat binary distribution on semimajor axes; Abt, 1983).