Welcome to this audio long read from nature.

In this episode, the golden age of neutron star physics has arrived.

Written by Adam Mann and read by Kerry Smith.

When a massive star dies in a supernova, the explosion is only the beginning of the end.

Most of the stellar matter is thrown far and wide, but the star's iron-filled heart remains behind.

This core packs as much mass as two suns and quickly shrinks to a sphere that would span the length of Manhattan. Crushing internal

pressure, enough to squeeze Mount Everest to the size of a sugar cube, fuses subatomic protons

and electrons into neutrons. Astronomers know that much about how neutron stars are born. Yet exactly

what happens afterwards, inside these ultra-dense cores, remains a mystery.

Some researchers theorise that neutrons might dominate all the way down to the centre.

Others hypothesise that the incredible pressure compacts the material into more exotic particles

or states that squish and deform in unusual ways. Now, after decades of speculation,

researchers are getting closer to solving the enigma, in part thanks to an instrument on the

International Space Station called the Neutron Star Interior Composition Explorer, or NISA, for

short. Last December, this NASA Space observatory provided astronomers with some of the most

precise measurements ever made of a neutron star's mass and radius, as well as unexpected

findings about its magnetic field.

The NISA team plans to release results about more stars in the next few months.

Other data are coming in from gravitational wave observatories, which can watch neutron stars contort as they

crash together. With these combined observations, researchers are poised to zero in on what fills

the innards of a neutron star. For many in the field, these results mark a turning point in the study of some of the universe's

most bewildering objects. This is beginning to be a golden age of neutron star physics,

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