Urca process

The Urca process is a cooling process in astrophysics through the emission of neutrinos in compact stellar objects. Compact stellar objects such as white dwarfs and neutron stars have a very small surface area and accordingly the cooling processes caused by electromagnetic radiation are very ineffective. With these stars, the energy loss via the emission of neutrinos is several orders of magnitude more effective, since neutrinos hardly interact with the matter due to the small cross-section .

In the Urca process, electron capture

( Z , A )

+

${\displaystyle e^{-}}$

→

(Z-1, A)

+

${\displaystyle {\nu }_{e}}$

and then through beta decay

(Z-1, A)

→

(Z, A)

+

${\displaystyle e^{-}}$

+ ${\displaystyle {\bar {\nu }}_{e}}$

Neutrinos are generated, these then leave the star unhindered. The Urca process shifts the mass boundary between a core collapse supernova and an electron capture supernova .

The term Urca process comes from George Gamow and Mario Schönberg . The first meeting of these two physicists took place in the Casino da Urca in Rio de Janeiro . They noted that this mechanism causes the thermal energy of neutron stars to disappear just as quickly as the money in the casino.

Individual evidence

1. ↑ DD Ofengeim, M. Fortin, P. Haensel, DG Yakovlev, JL Zdunik: Analytic approximations of neutrino luminosities and heat capacities of neutron stars with nucleon cores . In: Astrophysics. Solar and Stellar Astrophysics . 2016, arxiv : 1612.46723v1 .
2. ^ Wei-Hua Wang, Xi Huang, Xiao-Ping Zheng: Net reaction rate and neutrino emissivity for the Urca process in departure from chemical equilibrium . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1706.04498v1 .
3. ↑ Josiah Schwab, Lars Bildsten, Eliot Quataert: The Importance of Urca-process cooling in Accreting ONe White Dwarfs . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1708.07514v1 .
4. ^ Toshio Suzuki et al .: Electron capture and β-decay rates for sd-shell nuclei in stellar environments relevant to high density O-Ne-Mg cores . In: Astrophysics. Solar and Stellar Astrophysics . 2015, arxiv : 1512.00132v1 .
5. ↑ P. Haensel: Urca processes in dense matter and neutron star cooling . In: Space Science Reviews . 74, No. 3-4, 1995, pp. 427-436. bibcode : 1995SSRv ... 74..427H . doi : 10.1007 / BF00751429 .