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. The process was first discussed by George Gamow and Mario Schenberg while they were visiting a casino named Urca in Rio de Janeiro. Gamow is reported to have said to Schenberg that "the energy disappears in the nucleus of the supernova as quickly as the money disappeared at that roulette table." In Gamow's South Russian dialect, urca can also mean a robber or gangster.[1][2]

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

where B1 and B2 are baryons and l is a lepton. The baryons can be nucleons (free or bound), hyperons like Λ, Σ and Ξ, or members of the ∆ isobar. The lepton is either an electron or a muon.


1. ^ Urca process, entry in The Encyclopedia of Astrobiology, Astronomy, and Spaceflight, David Darling, accessed on line July 6, 2007.

2. ^ § 3, Gamow and the physics and evolution of stars, D. K. Nadyozhin, Space Science Reviews, 74, #3–4 (November 1995), pp. 455–461. DOI 10.1007/BF00751432.

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