X-ray Binaries in External Galaxies

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Handbook of X-ray and Gamma-ray Astrophysics

Abstract

X-ray appearance of normal galaxies is mainly determined by X-ray binaries powered by accretion onto a neutron star or a stellar mass black hole. Their populations scale with the star-formation rate and stellar mass of the host galaxy, and their X-ray luminosity distributions show a significant split between star-forming and passive galaxies, both facts being consequences of the dichotomy between high- and low-mass X-ray binaries. Metallicity, IMF and stellar age dependencies, and dynamical formation channels add complexity to this picture. The numbers of high-mass X-ray binaries observed in star-forming galaxies indicate quite high probability for a massive star to become an accretion-powered X-ray source once upon its lifetime. This explains the unexpectedly high contribution of X-ray binaries to the cosmic X-ray background, of the order of ∼10%, mostly via X-ray emission of faint star-forming galaxies located at moderate redshifts which may account for the unresolved part of the CXB. Cosmological evolution of the LX −SFR relation can make high-mass X-ray binaries a potentially significant factor in (pre)heating of intergalactic medium in the early Universe.

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Correspondence to Marat Gilfanov .

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© 2024 Springer Nature Singapore Pte Ltd.

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Gilfanov, M., Fabbiano, G., Lehmer, B., Zezas, A. (2024). X-ray Binaries in External Galaxies. In: Bambi, C., Santangelo, A. (eds) Handbook of X-ray and Gamma-ray Astrophysics. Springer, Singapore. https://doi.org/10.1007/978-981-19-6960-7_108

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