Take a star twice the mass of the sun and crush it to the size of Manhattan. One of the densest objects found anywhere in the universe would be a neutron star. Neutron stars are extraordinary astrophysical objects in their own right, but their extreme densities might also allow them to function as laboratories for studying fundamental questions of nuclear physics.
The "equation of state" (EoS) is a mystery to scientists because of the exotic conditions. The goal of modern astrophysics research is to determine this. A new piece of the puzzle, constraining the range of possibilities, has been found by a pair of scholars. Their work was published in a peer-reviewed journal.
The exotic objects are too small to be imaged with a standard telescope. The same way that one might use the length of two sides of a right-angled triangle to work out its hypotenuse is used by scientists to calculate the EoS. The radius of a star is hard to measure. One promising alternative for future observations is to use a quantity called the "peakspectral Frequency" in its place.
How is f2 measured? The laws of Einstein's Theory of Relativity allow for strong bursts of waves to be created. Scientists were the first to measure such emissions. The signal from the wobbling remnant of two merged stars can be used to calculate the peak wavelength.
Researchers believed that a direct, or "quasi-universal," correspondence existed between them. Raithel and Most have shown that this is not the case. A simple hypotenuse problem is not the same as determining the EoS. The angle between the two shorter sides is a third piece of information that one needs to calculate the longest side. The slope of the mass-radius relation is the third piece of information for Raithel and Most.
This new finding will allow researchers working with the next generation of LIGO to better utilize the data obtained from the merger of two stars. According to Raithel, the data could show the fundamental elements of the matter. According to Raithel, phase transitions could be dissolving the neutrons into sub-atomic particles. The stars have a sea of free quark matter in their interior. Tomorrow's researchers may be able to determine if phase transitions actually happen.
More information: Carolyn A. Raithel et al, Characterizing the Breakdown of Quasi-universality in Postmerger Gravitational Waves from Binary Neutron Star Mergers, The Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac7c75 Journal information: Astrophysical Journal Letters
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