Measure temperatures similar to those of star collisions in the laboratory

Collisions between neutron stars are fascinating cosmic events that lead to the formation of many chemical elements. Temperatures in these collisions are exponentially high, typically reaching hundreds of billions degrees Celsius.

The HADES collaboration, a large team of researchers working in different universities around the world, recently gathered the first-ever measurement of thermal electromagnetic radiation produced during star collisions, called black body radiation, in the laboratory. Their study, described in an article published in Physical Nature, led to the observation of temperatures of about 800 billion degrees Celsius, comparable to those that occur in collisions between stars.

"In our study, we smashed nuclei (gold nuclei for example)," said Joachim Stroth, spokesperson for the HADES collaboration, at Phys.org. "This produces material forms under conditions that do not normally exist, only neutron stars reach such densities (or even higher) and when neutron stars fuse, their temperature can reach the level of our This is why we can form a type of material in the laboratory. "

In their study, Stroth and his colleagues used the HADES detector system at the GSI / FAIR accelerator center in Darmstadt to collect new information on the collisions of two heavy-duty relativistic nuclei. This allowed them to gather extensive laboratory observations on the microscopic properties of extreme states of matter, cosmic type.

The researchers specifically created quantum chromodynamics (QCD) material as a transient state by collision of heavy ions at relativistic energies. This type of material can exist at different phases depending on a variety of factors including temperature, pressure and baryochemical potential.

By observing the states of the QCD material, the researchers hoped to better understand the matter of star neurons and collisions. A key question they looked at was whether the constituents of nuclei, which are essentially building blocks of matter, can change their properties under extreme conditions.

"We measured the electromagnetic radiation thus emitted by the fireballs formed during the collision," explained Stroth. This radiation can tell us a lot about the properties of the constituents. However, it is difficult to achieve this measure because fireballs live very little time (10²² s) and radiation is rarely emitted. "

Hadrons are composite particles composed of three quarks (baryon) of an antiquark and a quark (meson) held together by the powerful force. When these particles disintegrate, they sometimes produce virtual photons, which can not be detected directly because their existence violates the conservation of energy and momentum.

These virtual photons, which carry all the information on disintegrated subatomic particles, immediately disintegrate into pairs of electrons (that is, an electron and a positron). In their study, Stroth and his colleagues detected these particles with the help of a spectrometer.

"We observed that the temperature in the collision zone could reach 800 billion degrees and that the density could reach three times the nuclear saturation density," said Stroth. "We find that in such conditions, the building blocks of the material are drastically altered, which also means that the properties of the material are very different, as if the building blocks retained their properties."

The HADES collaboration is the first research team to successfully measure temperatures similar to those encountered during star collisions in the laboratory. The findings of this team could significantly improve the current scientific understanding of neutron star fusion events, while illuminating the production of matter from quarks and elemental gluons.

"We are building a new experience for HADES that will be operating in the new FAIR facility from 2025," said Stroth. "With this detector, we will be able to extend measurements to higher temperatures and density."

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