How a Neutron Star Cooled Off in Just Four Days ⚡ экспресс
After a powerful X-ray superburst, the neutron star in the MAXI J1752–457 system cooled down in just 4 days — spotted by the MAXI and NinjaSat space observatories. Researchers believe the cause was the Urca nuclear cycle: in the star's ocean (a dense layer beneath the crust), pairs of odd-numbered isotopes alternately capture electrons and emit neutrinos, efficiently carrying heat away. This is the first observational hint of such a process in neutron stars. The ignition temperature reached ~4 billion degrees, and the Urca cycle dominated for about 2 days. Unlike ordinary X-ray bursts that happen closer to the surface, this superburst dug into deep layers, opening a way to study their composition via the cooling rate.
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.