Researchers rather rely on indirect properties that they can measure– such as the mass and radius of a neutron star– to calculate the EoS. Accidents in between neutron stars, which are governed by the laws of Einsteins Theory of Relativity, lead to strong bursts of gravitational wave emission. “At least in principle, the peak spectral frequency can be determined from the gravitational wave signal released by the wobbling residue of 2 merged neutron stars,” says Most.
According to Raithel, this information could reveal the essential constituents of neutron star matter. “Some theoretical predictions suggest that within neutron star cores, phase shifts could be liquifying the neutrons into sub-atomic particles called quarks,” stated Raithel.
Since of these exotic conditions, scientists still do not comprehend what precisely neutron stars themselves are made from, their so-called “equation of state” (EoS). Identifying this is a significant objective of modern astrophysics research. A new piece of the puzzle, constraining the series of possibilities, has actually been found by a set of scholars at the Institute for Advanced Study (IAS): Carolyn Raithel, John N. Bahcall Fellow in the School of Natural Sciences; and Elias Most, Member in the School and John A. Wheeler Fellow at Princeton University. Their paper was published recently in The Astrophysical Journal Letters.
Neutron stars are so thick, that a single teaspoon of one would have a mass of about a trillion kgs.
Neutron star merger and the gravity waves it produces. Credit: NASA/Goddard Space Flight Center
Preferably, astrophysicists wish to look inside these exotic things, but they are far-off and too little to be imaged with basic telescopes. Researchers instead count on indirect properties that they can determine– such as the mass and radius of a neutron star– to calculate the EoS. This is much like how one may utilize the length of two sides of a right-angled triangle to exercise its hypotenuse. However, one problem here is that the radius of a neutron star is extremely difficult to measure precisely. An appealing option for future observations is to instead use a quantity called the “peak spectral frequency” (or f2) in its place.
Accidents between neutron stars, which are governed by the laws of Einsteins Theory of Relativity, lead to strong bursts of gravitational wave emission. “At least in concept, the peak spectral frequency can be calculated from the gravitational wave signal released by the wobbling remnant of two combined neutron stars,” says Most.
Doomed neutron stars whirl toward their death in this animation. Gravitational waves (pale arcs) bleed away orbital energy, causing the stars to move better together and merge. As the stars collide, a few of the particles blasts away in particle jets moving at almost the speed of light, producing a quick burst of gamma rays (magenta). In addition to the ultra-fast jets powering the gamma rays, the merger also creates slower-moving debris. An outflow driven by accretion onto the merger residue gives off rapidly fading ultraviolet light (violet). A dense cloud of hot debris removed from the neutron stars prior to the collision produces infrared and visible light (blue-white through red). The UV, optical, and near-infrared radiance is jointly referred to as a kilonova. Later, once the residues of the jet directed towards us had actually broadened into our view, X-rays (blue) were found. This animation represents phenomena observed as much as nine days after GW170817. Credit: NASAs Goddard Space Flight Center/CI Lab
Rather, it is more comparable to calculating the longest side of an irregular triangle, where one likewise requires a third piece of info: the angle in between the 2 much shorter sides. For Raithel and Most, this third piece of details is the “slope of the mass-radius relation,” which encodes info about the EoS at greater densities (and hence more extreme conditions) than the radius alone.
This new finding will allow researchers dealing with the next generation of gravitational wave observatories (the successors of the currently operating LIGO) to better use the information obtained following neutron star mergers. According to Raithel, this information could reveal the fundamental constituents of neutron star matter. “Some theoretical predictions recommend that within neutron star cores, phase shifts might be dissolving the neutrons into sub-atomic particles called quarks,” specified Raithel. “This would indicate that the stars contain a sea of totally free quark matter in their interiors. Our work may help tomorrows scientists identify whether such stage transitions actually happen.”
Reference: “Characterizing the Breakdown of Quasi-universality in Postmerger Gravitational Waves from Binary Neutron Star Mergers” by Carolyn A. Raithel and Elias R. Most, 13 July 2022, The Astrophysical Journal Letters.DOI: 10.3847/ 2041-8213/ ac7c75.
Credit: NASAs Goddard Space Flight Center/CI Lab
The result would be a neutron star– one of the densest things discovered anywhere in the Universe. Neutron stars are amazing astrophysical objects in their own right, their severe densities might also permit them to operate as laboratories for studying fundamental questions of nuclear physics, under conditions that might never ever be recreated on Earth.