- Art Gallery -

In astroparticle physics, an Urca process is a reaction which emits a neutrino and which is assumed to take part in cooling processes in neutron stars and white dwarfs. The process was first discussed by George Gamow and Mário Schenberg while they were visiting a casino named Cassino da Urca in Rio de Janeiro. As Gamow recounts in his autobiography, the name was chosen in part to commemorate the gambling establishment where the two physicists had first met, and "partially because the Urca Process results in a rapid disappearance of thermal energy from the interior of a star, similar to the rapid disappearance of money from the pockets of the gamblers on the Casino de Urca."[1] In Gamow's South Russian dialect, urca (Russian: урка) can also mean a robber or gangster.[2][3]

The direct Urca processes are the simplest neutrino-emitting processes and are thought to be central in the cooling of neutron stars. They have the general form

\( B_1 \) → \( B_2 \) + ℓ + \( \bar{ \nu _{l}} \) ,
\( B_2 \) + ℓ → \( B_1 \) + \( \nu _{l} \),

where \( B_1 \) and \( B_2 \) are baryons, ℓis a lepton, and \( \nu _{l} \), (and \( \bar{ \nu _{l}} \)) are (anti-)neutrinos. The baryons can be nucleons (free or bound), hyperons like Λ, Σ and Ξ, or members of the Δ isobar. The lepton is either an electron or a muon.

The Urca process is especially important in the cooling of white dwarfs, where a lepton (usually an electron) is absorbed by the nucleus of an ion and then convectively carried away from the core of a star. Then, a beta decay occurs. Convection then carries the element back into the interior of the star, and the cycle repeats many times. Because the neutrinos emitted during this process are unlikely to be reabsorbed, this is effectively a cooling mechanism for white dwarfs.[4]

The process can also be essential in the cooling of neutron stars. If a neutron star contains a central core in which the direct Urca-process is operative, the cooling timescale shortens by many orders of magnitude.[5]

Gamow, George. My World Line: An Informal Autobiography. New York: The Viking Press. p. 137.
D. Darling. "Urca process". The Internet Encyclopedia of Science. Retrieved 2 March 2010.
D. K. Nadyozhin (1995). "Gamow and the physics and evolution of stars". Space Science Reviews. 74 (3–4): 455–461. Bibcode:1995SSRv...74..455N. doi:10.1007/BF00751432.
M. Brueggen; A. Kercek (10 January 2000). "The convective URCA process in white dwarfs". Max Planck Institute. Archived from the original on 12 January 2010. Retrieved 5 February 2010.

P. Haensel (1995). "Urca processes in dense matter and neutron star cooling". Space Science Reviews. 74 (3–4): 427–436. Bibcode:1995SSRv...74..427H. doi:10.1007/BF00751429.


Neutron star

Radio-quiet Pulsar

Single pulsars

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


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


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


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


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


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


White dwarf

Chandrasekhar limit PG 1159 star Stellar evolution Hertzsprung–Russell diagram Mira variable


Black dwarf Type Ia supernova
Candidates Neutron star
Pulsar Magnetar Related links Stellar black hole
Related links Compact star
Quark star Exotic star Extreme helium star Subdwarf B star Helium planet

In binary

Remnant List Dwarf nova Symbiotic nova Cataclysmic variable star
AM CVn star Polar Intermediate polar X-ray binary
Super soft X-ray source Binary pulsar
X-ray pulsar List Helium flash Carbon detonation


Pulsating Urca process Electron-degenerate matter Quasi-periodic oscillations


Planetary nebula
List RAMBOs White dwarf luminosity function Timeline of white dwarfs, neutron stars, and supernovae

Physics Encyclopedia



Hellenica World - Scientific Library

Retrieved from "http://en.wikipedia.org/"
All text is available under the terms of the GNU Free Documentation License