The ability to measure gravitational waves of two merging neutron stars has made it possible to answer some of the key questions about the structure of matter. At extremely high temperatures and densities in the merger, scientists suggest a phase transition in which neutrons dissolve in their constituents: quarks and gluons. In the current issue of Physical Review Letters, two international research groups reported their calculations on how the signature of such a phase transition would appear in a gravitational wave.
Quarks, the smallest blocks of matter, never appear on their own. in nature. They are always tightly connected within protons and neutrons. However, neutron stars, weighing as much as the Sun, but which are only the size of the city of Frankfurt, have a core so dense that a transition from neutron to quark matter can occur. Physicists call this process a phase transition, similar to the liquid-steam transition in the water. In particular, such a phase transition is generally possible when the fusion of neutron stars forms a very massive metastable object with densities exceeding atomic nucleus density and at temperatures that are 10,000 times higher than at the core of the Sun.
emitted by the fusion of neutron stars can serve as the ambassador of the possible phase transitions in space. The phase transition must leave a characteristic signature in the gravitational wave signal. The research groups from Frankfurt, Darmstadt and Ohio (Goethe University / FIAS / GSI / Kent University), as well as from Darmstadt and Wroclaw (GSI / Wroclaw University) use modern supercomputers to calculate how this signature might look. For this purpose, they used different theoretical phase transition models
. In the event that the phase transition occurs more after the actual merger, small quarks will appear gradually in the merged entity. "With the help of Einstein's equations, for the first time, we have succeeded in showing that this subtle change in structure will lead to a deviation in the gravitational wave signal, while the newly formed massive neutron star shrinks below explains Luciano Rezola, professor of theoretical astrophysics at Goethe University.
In the computer models of Dr. Andreas Baushen from GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt The phase transition already occurs immediately after the merger – a core of quark matter is formed inside the central object. "We have succeeded in showing that there will be a pronounced change in the frequency of the gravitational wave signal in this case," said Bassey. "In this way, we identified a measurable criterion for phase transition in neutron star stargate gravity waves in the future."
Not all details of the gravitational wave signal are still measurable with current detectors. They will, however, become visible both in the next generation of detectors and in a relatively close to us merger event. An additional quark-response approach is offered by two experiments: By colliding heavy ions into the existing HADES setting in the GSI and the future CBM detector in the FAIR currently under construction . GSI will produce compressed nuclear matter. In collisions, it may be possible to create temperatures and densities that are similar to those of a neutron star merger. Both methods give a new idea of the emergence of phase transitions in nuclear matter and thus its basic properties.