How a Neutron Star Cooled Off in Just Four Days ⚡ экспресс
The rapid cooling of the neutron star in the MAXI J1752–457 system within 4 days after an X-ray superburst, recorded by the MAXI and NinjaSat satellites, is explained by enhanced neutrino emission from cycles of electron capture and β− decay of odd nuclei (Urca pairs) in the stellar ocean. This is the first observational evidence for the 'Urca nuclear process.' The observations point to a hot ignition layer with a maximum temperature of ~4 GK, located near the Urca shell of the ocean; the Urca nuclear process dominated up to ~2 days after the superburst. This behavior differs from ordinary type I X-ray bursts, triggered by hydrogen or helium burning in much shallower layers. The data open up the possibility of studying superburst ashes via Urca pairs through long-term monitoring of crust cooling on timescales of days.
In April 2023, Japanese satellites detected a super-intense X-ray burst on the neutron star MAXI J1752–457. The star cooled down in 4 days — five times faster than usual. Like someone cracked open a cosmic window.
That window was flung wide by the nuclear 'Urca process.' In an ocean of atomic nuclei hundreds of meters thick, protons and neutrons trade electrons, giving birth to neutrinos. These ghost particles zoom away instantly, carrying off heat like a draft sweeps out warm air.
Surprisingly, the mechanism kicks in only at a billion degrees; a slightly lower temperature and cooling would drag on for years. Ordinary bursts, burning hydrogen and helium at the surface, don't open such a window. Now, by the cooling speed, we can study the interiors of these ultra-dense objects.
🎯 The name 'Urca' was coined in a casino: physicists George Gamow and Mario Schönberg joked that neutrinos carry away energy as relentlessly as a croupier takes chips.