A neutron star

Neutron stars are some of the densest objects in the Universe. The material inside gets squeezed so hard that scientists don't yet know what form it takes. The core of a neutron star might be made of a thick soup of quarks, or contain exotic particles that couldn't survive anywhere else in the Universe.

Since we can't directly look inside a neutron star, and we can't recreate one on Earth, scientists have been comparing many different possible models – called 'equations of state' – to measurements of neutron stars taken from afar. While the behaviour of individual neutron stars may depend on properties like their mass or how fast they spin, all neutron stars must obey the same equation of state.

The discovery of three remarkably young and cold neutron stars shows that they are capable of cooling down rapidly. They did this by sending out trillions of tiny particles called neutrinos via the so-called 'direct Urca process'. As much as three quarters of known neutron state models don't incorporate this cooling mechanism, so this finding brings us a big step closer to uncovering the one equation of state to rule them all!

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[Image description: An artist impression of a neutron star, shown as a bright blue and red sphere with spark-like features flying off it. Several blue magnetic field lines loop connect the sphere's two poles. The sphere is surrounded by a see-through blue cloud, and with a red cloud on the sides of the image. Stars are visible in the background.]