A neutron star is the dead core of a star that once exploded, compressed to the size of a city. If a normal star is nearby, the neutron star siphons matter from it like a vacuum cleaner. This matter falls onto the surface and forms a crust — a solid layer of neutron-rich atomic nuclei. In this crust, nuclear transformations take place: some elements decay into others, emitting particles — neutrinos. Neutrinos barely interact with matter and carry heat away from the star like an invisible fan.
Scientists at the University of Michigan measured how often such decays occur in the nuclei of scandium-57, titanium-57, and titanium-59. They used two detectors: one caught gamma rays, the other caught neutrons emitted after the decay. It turned out that titanium decays occur 2–3 times less frequently than theory predicted. And scandium-57 does not transition to the ground state of another nucleus at all: it seems to take a step backward rather than forward.
This means that neutrino cooling in neutron star crusts is weaker than previously thought. For astronomers, this matters: X-ray bursts, called superbursts, may last longer or be less bright. Now, models of neutron star cooling will need to be revised to more accurately read signals from the depths of space.
A neutron star the size of a city weighs more than the Sun. A teaspoon of its material on Earth would weigh billions of tons.
In Robert Forward's novel "Dragon's Egg," creatures live on the surface of a neutron star, with chemistry based on nuclear reactions, like the crust studied in this article.