Bondi accretion

In astrophysics, the Bondi accretion, named after Hermann Bondi, is spherical accretion onto a compact object traveling through the interstellar medium. It is generally used in the context of neutron star and black hole accretion. To achieve an approximate form of the Bondi accretion rate, accretion is assumed to occur at a rate

$\dot{M} \simeq \pi R^2 \rho v,$

where $\rho$ is the ambient density, $v$ is either the velocity of the object or the sound speed $c_{s}$ in the surrounding medium if the object's velocity is lower than the sound speed, and the Bondi radius $R$ provides an effective area. The effective radius is acquired by equating the object's escape velocity and the relevant speed, i.e.

$\sqrt{\frac{2 G M}{R}} \simeq c_s,$

$R\simeq\frac{2 G M}{c_s^2}$ .

The accretion rate therefore becomes

$\dot{M} \simeq \frac{4 \pi \rho G^2 M^2 }{c_s^3}$ .

These are only scaling relations rather than rigorous definitions. A more complete solution can be found in Bondi's original work and two other papers.

Bibliography

Bondi (1952) MNRAS 112, 195, link
Mestel (1954) MNRAS 114, 437, link
Hoyle and Lyttleton (1941) MNRAS 101, 227

References

Neutron star

Types	Radio-quiet Pulsar

Single pulsars	Magnetar Soft gamma repeater Anomalous X-ray Rotating radio transient

Binary pulsars	Binary X-ray X-ray binary X-ray burster List Millisecond Be/X-ray Spin-up

Properties	Blitzar Fast radio burst Bondi accretion Gamma-ray burst Glitch Neutronium Neutron-star oscillation Optical Pulsar kick Quasi-periodic oscillation Relativistic Rp-process Starquake Timing noise Tolman–Oppenheimer–Volkoff limit Urca process

Related	Compact star Quark star Exotic star Supernova Supernova remnant Related links Hypernova Quark-nova White dwarf Related links Stellar black hole Related links Radio star Pulsar planet Pulsar wind nebula Thorne–Żytkow object

Discovery	LGM-1 Centaurus X-3 Timeline of white dwarfs, neutron stars, and supernovae

Satellite investigation	Rossi X-ray Timing Explorer Fermi Gamma-ray Space Telescope Compton Gamma Ray Observatory Chandra X-ray Observatory

Other	X-ray pulsar-based navigation Tempo software program Astropulse The Magnificent Seven

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