Space | The collision of neutron stars can produce the densest matter in the universe – Finnish scientists figuring out how to find it

If black holes are incomprehensible to the layman, neutron stars are probably a good second in the race of strange phenomena in space.

They probably contain matter that cannot be found anywhere else in the universe. This so-called Finnish researchers are also investigating the essence of quark matterlike a professor Aleksi Vuorinen at the University of Helsinki.

Finns can be part of an international group now a new way prove the existence of a mystical substance.

For that, a collision of neutron stars is needed, the traces of which can be measured. Signs of quark matter can be found in the wake of the collision. It would be a sensation.

Neutron stars are extremely dense stars collapsed under the influence of gravity.

As their name suggests, they consist mainly of neutrons, which are uncharged particles in the nucleus of an atom. They are thrown out, for example, in the chain reactions of nuclear power plants and nuclear bombs.

Neutron stars are just over twenty kilometers in diameter, but insanely dense. If humanity were the stuff of a neutron star, we’d all fit in a lump of sugar.

Neutron stars are so tightly compressed that they just barely survive. If you throw a shovelful of sand at the heaviest possible neutron star, it will collapse into a black hole due to a small increase in mass.

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Neutron stars are the only “laboratories” where quark matter exists today.

If two neutron stars happen to collide, so-called quark matter is apparently created. It is quite similar to the matter that the very young universe was filled with.

It was a so-called quark gluon plasma. It is only produced in extreme heat.

First of all, it has quarks, the smallest parts of matter. Today, quarks form the core particles of atoms, i.e. protons and neutrons. In the heat of the beginning of the universe, these did not have time to be born, but the quarks ran free.

There were still other particles in it, gluons, which nowadays glue the quarks together.

“The quark gluon plasma dominated the universe for about a billionth of a second. However, as far as I know, its quark density was lower than in collisions between neutron stars,” the university lecturer Niko Jokela from the University of Helsinki says.

Massive neutron stars may even have large cores composed of quark matter. In any case, according to Jokela, neutron stars are the only “laboratories” where quark matter could exist today.

Quark matter could perhaps be observed from collisions of neutron stars. According to Jokela and another international group, one could look for signs in the gravitational waves sent out by the collision.

These gravitational waves are created when massive objects such as black holes or neutron stars collide. The collision causes space to ripple like a big rubber mat to which a bowling ball is thrown.

Gravitational waves have been observed since 2015, when the Ligo observatories in the United States were the first to detect them. The researchers produced a certain kind of curve from the observation. It said that two black holes had twisted together.

The collision of two neutron stars was reported in 2017.

In the future, there may be certain signs in the corresponding gravitational wave curves that reveal the creation of quark matter in neutron star collisions. US Space Administration modeling of such a collision can be found on Youtube.

Of quark matter the existence could be recognized from the curve. The reason is that quark matter behaves differently than neutrons. In the end, it’s all about the difference in the so-called volume viscosity.

“We could think of the difference between quark matter and neutron matter like kneading dough. Soft dough is easier to knead, it molds and stretches more easily. It means that less energy is needed to modify it,” Jokela describes.

Correspondingly, quark matter is more easily compressed than neutron matter, especially at the high temperatures of neutron star collisions.

The group was able to determine the bulk viscosity of this quark matter.

“In order to find quark matter in gravitational waves, the effect of viscosity should be added to current collision modeling”, academy researcher Risto Paatelainen says.

Gravitational waves are found by first modeling numerous collisions. With the help of modeling, weak signals can be found among the disturbances of extremely sensitive devices.

In international In addition to Jokela, Paatelainen and Vuorinen, the group had a group leader Matti Järvinen From the Asia Pacific Center for Theoretical Physics research institute in South Korea, professor Aleksi Kurkela from the University of Stavanger and Ph.D Saga Säppi from the Technical University of Munich.