Like a funhouse mirror, this gravitational distortion makes the neutron star appear bigger than it really is. Neutron stars’ gravity is so extreme, it bends the path of light leaving the surface.

Obtaining the mass of a neutron star is easy, at least if the neutron star has a stellar companion whirling around it. From there they can use well-understood physics to calculate how pressure changes with density, a relation known as the equation of state, and then compare that equation to the nuclear physicists’ offerings. To tell which idea is right, astronomers must do something deceptively simple: measure these objects’ mass and radius. “But the problem is you can't really calculate this once you go past a couple of particles.” So nuclear physicists use approximations and assumptions to predict the behavior of lots of particles - and they come up with a variety of answers. “We have a theory for how quarks and gluons behave this is quantum chromodynamics,” Miller says. But in fact nuclear physicists offer many answers to the riddle of neutron star interiors. Here, the matter may transform again, releasing even the quarks that make up neutrons. NASA’s Goddard Space Flight Center / Conceptual Image Labĭeeper still, in the core, the density reaches something like twice that of an atomic nucleus. The state of matter in their inner cores remains unknown. Neutron stars are not all neutrons - they likely have layers of different material. Most protons merge with electrons only a smattering remain for stability. As gravitational pressure increases with depth, the neutrons squeeze out of the nuclei, which eventually dissolve completely. Their crystalline crusts contain relatively ordinary electrons and ions (the latter of which are made of neutrons and protons). However, there’s more to neutron stars than what’s in their name - they’re at most 95% neutrons and possibly even less. Lifting a teaspoon of this matter would be a feat similar to drinking empty a horn attached to the ocean - even Thor could not lift 4 billion tons. The stars are poised on the edge, just this side of collapsing into a black hole, and the immense gravitational pressure squeezes their electrons and protons into neutrons. Neutron stars are the cinders left when massive stars implode, shedding their outer layers in supernova explosions. These studies, now undergoing scientific review, suggest that nuclear physicists might need to rethink what happens in the stars’ ultra-dense cores. Members of the NICER team presented two independent size measurements of the most massive neutron star known at the recent virtual meeting of the American Physical Society. Their age, their temperature, even their size is not always what it first appears to be.īut with the Neutron star Interior Composition Explorer (NICER) aboard the International Space Station, astronomers are finally beginning to make some headway measuring these stars’ actual size - and with that, some insight into their strange interiors. Neutron stars are the tricksters of the celestial sphere.

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