Gravitational Waves Might Allow Us To Study The Interior Of Neutron Stars Before They Collide

The results from a numerical relativity simulation of two merging neutron stars similar to GW170817. University of Birmingham

New research suggests that by using gravitational waves we might be able to learn a lot more about the interior of neutron stars. These peculiar objects are one of the end-products of supernova and are so dense that one teaspoon of neutron star would weigh about 10 million tons.

The properties of this material are not exactly clear and many theoretical studies and observation campaigns have tried to work it out. As reported in Nature Communication, help might come in the form of gravitational waves.

Researchers have created a simulation of what happens as a pair of neutron stars are about to collide. The two objects began oscillating and the model shows that as the neutron stars become deformed under the influence of tidal forces, these oscillations (in the form of characteristic frequencies) are imprinted on the gravitational wave signals.

“As the two stars spiral around each other, their shapes become distorted by the gravitational force exerted by their companion. This becomes more and more pronounced and leaves a unique imprint in the gravitational wave signal,” lead author Dr Geraint Pratten of the University of Birmingham's Gravitational Wave Institute said in a statement.

“The tidal forces acting on the neutron stars excite oscillations inside the star giving us insight into their internal structure. By measuring these oscillations from the gravitational-wave signal, we can extract information about the fundamental nature and composition of these mysterious objects that would otherwise be inaccessible.”

This, the researchers hope, makes asteroseismology – the study of stellar oscillations – with gravitational waves a vital new tool for understanding the elusive nature of incredibly dense nuclear matter.

The first detection of a collision between neutron stars was in 2017 and it has given us amazing new insights on the final moments of these peculiar stars. A crucial factor was the presence of strong theoretical models to which the signal could be matched. By improving those, there is certainly a chance of understanding neutron stars better.

“The more information we can gather by developing ever more sophisticated theoretical models, the closer we will get to revealing the true nature of neutron stars,” co-lead author Dr Patricia Schmidt added.

New gravitational observatories, such as the Laser Interferometer Space Antenna, will also be key to this as they will produce more detailed observations of the events.

The material inside neutron stars is believed to be the strongest in the universe. It is nothing like any substance we can experience on Earth and it is organized in peculiar structures that astronomers referred to as nuclear pasta, for no other reason than they look a bit like the Italian specialty in simulations.

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