BondiHoyleLyttleton

BondiHoyleLyttleton, often abbreviated as BHL, refers to a significant theoretical model in astrophysics concerning the accretion of matter onto a central body. The theory, developed by Hermann Bondi, Fred Hoyle, and Raymond Lyttleton, describes how a massive object, such as a star or a black hole, can capture gas and dust from its surroundings. The core concept is that as the central object moves through an interstellar medium, it creates a gravitational wake, and matter within a certain radius, known as the Bondi accretion radius, can be drawn in.

The BHL model assumes a steady, spherically symmetric accretion flow onto a non-rotating, uncharged point mass. It calculates the rate at which matter falls onto the central object based on the object's mass, its velocity relative to the ambient medium, and the density of that medium. This theoretical framework has been crucial for understanding phenomena like the fueling of active galactic nuclei, the formation of protostellar disks, and the accretion onto neutron stars and white dwarfs in binary systems.

While the original BHL model provides a foundational understanding, it has been extended and refined over time to account for more complex scenarios, such as the effects of magnetic fields, rotation of the central object, and deviations from spherical symmetry. Despite these advancements, the fundamental BHL accretion rate remains a vital benchmark in astrophysical accretion theory.