Collisions between neutrons and stars could reveal the mysterious matter of a quark



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A simulation of colliding neutron stars
Graphic: C. Breu, L. Rezzolla

Scientists are imagining ways to probe the nature of the smallest bits of the Universe – the quarks – by observing the ultra-dense neutron stars that collide.

Particle colliders in Switzerland and Long Island, New York State, have each highlighted a whole new form of matter in which quarks, rather than atoms, constitute the basic unit. . But scientists believe that neutron star collisions should also produce this type of material, and think they can detect them with the help of gravitational wave detectors.

"We want an independent way to see the quark issue," Gizmodo Veronica Dexheimer, an assistant professor of physics at Kent State University, told Gizmodo.

The material is usually composed of atoms, themselves composed of electrons, protons and neutrons; these protons and neutrons are themselves made of quarks. But at sufficiently high energies and pressures, matter passes through a phase transition in quarks or quark-gluon plasma, in which the constituent parts of protons and neutrons – the quarks – are no longer confined to atoms. and become the smallest component of matter.

In general, scientists create quark matter in colliders by snapping high-energy atoms. But you do not think that the enormous energy of colliding neutron stars – stellar corpses as large as the Sun but only a few kilometers wide – would also create this type of problem.

The scientists announced the first recorded occurrence of two neutron stars slamming together in August 2017, an event observed by the space-time ripples, called gravitational waves, that they produced. Two new articles published this week in Physical Review Letters use computer simulations to predict two potential ways to observe the quark-produced material during neutron star collisions, depending on their impact on the signal from the Gravitational wave.

An article by German researchers, as well as Dexheimer, proposes that colliding neutron stars present a gravitational waveform of different shape with a different phase after the fusion of neutron stars than the theory provides otherwise. This would result from the gradual formation of quark materials throughout the collision before the entire system collapses into a black hole.

Another article from an international team of researchers suggests that the collision immediately forms a core of quark matter in the center. This would cause oscillation of gravitational waves with higher frequencies than expected after fusion.

I asked one author of each article what he thought of the research of the other, and both of them essentially felt that they represented two different and compatible ways of looking for a similar phenomenon.

Both research teams have the same requirements to be able to formulate their observations: they need upgrades in gravitational wave observatories such as LIGO, based in the United States, and Virgo, based in Europe. "Basically, we need a higher sensitivity of detectors at high frequencies and a particularly close event," said Andreas Bauswein, a physicist at the GSI Helmholtz Heavy Ion Research Center in Darmstadt, Germany. These events should be as close if not closer than those of August 2017, which occurred at 40 megaparsec (130 million light years) from Earth.

Now that scientists have observed the gravitational waves of black holes and colliding neutron stars, the excitement lies in what these waves could tell us about the nature of our strange universe.

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