Stellar Echoes: What Neutron Stars Conceal ✎ express
We know about neutron stars thanks to the work of Fritz Zwicky, Subrahmanyan Chandrasekhar, and Jocelyn Bell Burnell. They are former cores, squeezed to city size: a teaspoon of their matter weighs as much as Mount Everest. Now scientists have figured out how to peer inside these objects without prying them open.
When ripples in spacetime from a catastrophe strike a neutron star, it responds with a complex ringing. First comes a direct strike-reflection, then a series of fading echoes, like the dying ring of a bell. The wave bounces around inside, where spacetime is warped by incredible gravity, each time emerging a little later and fainter. Scientists have learned to split this rumble into discrete steps. Each echo is a snapshot of a certain depth.
Now, by analyzing the sequence of echoes, we can build a map of the star, just as light analysis reveals the makeup of distant luminaries. Future detectors will be able to listen to the echoes of these cosmic thuds, like an interstellar stethoscope.
A neutron star is the core of a former star, squeezed to city size. A teaspoon of its matter weighs as much as Mount Everest.
In science fiction, picking up echoes from invisible objects is a common trope. In Carl Sagan's novel 'Contact,' the alien signal was also multilayered, like an echo.