08-13-2021-2253 - Bondi Accretion

 In astrophysics, the Bondi accretion (also called Bondi-Hoyle-Lyttleton 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 

.

Where: 

•  is the ambient density
•  is the object's velocity  or the sound speed  in the surrounding medium if 
•  is the Bondi radius, defined as .

The Bondi radius comes from setting escape velocity equal to the sound speed and solving for radius. It represents the boundary between subsonic and supersonic infall.^[1] Substituting the Bondi radius in the above equation yields:

.

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.

Application to accreting protoplanets[edit]

When a planet is forming in a protoplanetary disk, it needs the gas in the disk to fall into its Bondi sphere in order for the planet to be able to accrete an atmosphere. For a massive enough planet, the initial accreted gas can quickly fill up the Bondi sphere. At this point, the atmosphere must cool and contract (through the Kelvin–Helmholtz mechanism) for the planet to be able to accrete more of an atmosphere.

Bibliography[edit]

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

References[edit]

1. ^ Edgar, Richard (21 Jun 2004). "A Review of Bondi-Hoyle-Lyttleton Accretion". A Knowledgebase for Extragalactic Astronomy and Cosmology. New Astronomy Reviews. doi:10.1016/j.newar.2004.06.001. Retrieved 19 February 2018.

hide v t e Neutron star
Types	Radio-quiet Pulsar
Single pulsars	Magnetar  Soft gamma repeater Anomalous X-ray Rotating radio transient
Binary pulsars	Binary X-ray pulsar  X-ray binary X-ray burster List Millisecond Be/X-ray Spin-up
Properties	Blitzar  Fast radio burst Bondi accretion Chandrasekhar limit 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	Gamma-ray burst progenitors Asteroseismology Compact star  Quark star Exotic star Supernova  Supernova remnant Related links Hypernova Kilonova Neutron star merger 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
Category  Commons

This physics-related article is a stub. You can help Wikipedia by expanding it. https://en.wikipedia.org/wiki/Bondi_accretion