For the first time, astrophysicists have measured the temperature of elementary particles in the radioactive aftermath of a neutron star collision that led to the formation of a black hole.

This discovery allows scientists to investigate the microscopic physical properties of these powerful cosmic events. The results also show how individual observations capture an object’s existence over time, like a snapshot spanning a cosmic moment. Researchers from the Niels Bohr Institute at the University of Copenhagen made the discovery, which was recently published in the journal Astronomy and Astrophysics.

New observations reveal formation of heavy elements

The collision of two neutron stars created the smallest black hole ever observed. This intense cosmic event created a fireball that expanded at nearly the speed of light, shining with the brightness of hundreds of millions of suns in the days following the impact. This extremely bright object, called a kilonova, emits large amounts of radiation due to the decay of heavy radioactive elements formed during the explosion.

By combining kilowatt light measurements from telescopes around the world, an international research team led by the Cosmic DAWN Center at the Niels Bohr Institute has reached a conclusion about the mysterious nature of the burst and is moving closer to an answer. Old astrophysics question: Where do elements heavier than iron come from?

The role of global observatories in tracking astrophysical events

“This astrophysical explosion evolves dramatically every hour, so no single telescope can track the entire history. Individual telescopes’ view of the event is obscured by the Earth’s rotation.”

However, by combining measurements from Australia, South Africa and the Hubble Space Telescope, we can follow its development in great detail. “We show that the whole is more than the sum of individual data sets,” says Albert Snappen, a postdoctoral researcher at the Niels Bohr Institute and leader of the new study.

Extreme temperatures resulting from collisions of neutron stars

Immediately after the collision, the fragmented stellar material reaches temperatures of billions of degrees. It is a thousand times hotter than the center of the Sun and is comparable to the temperature of the universe just one second after the Big Bang.

This extreme temperature causes electrons to not bond to the atomic nucleus but instead float in what is known as ionized plasma. Electrons “dance” around. However, in the following moments, minutes, hours and days, the star matter cools, as does the entire universe after the Big Bang.

Evidence of heavy elements in after-collision glow

370,000 years after the Big Bang, the universe cooled enough for electrons to join atomic nuclei to form the first atoms. Because light was no longer blocked by free electrons, it could travel freely through the universe.

This means that the oldest light we can see in the history of the universe is a patch of light that forms the distant background of the night sky, called “cosmic background radiation.” A similar process in which electrons combine with atomic nuclei can now be observed in the stellar material of the explosion.

One particular result is the observation of heavy elements such as strontium and yttrium. They are easy to detect, but it is likely that many other heavy elements were formed in the explosion, the origin of which we are not sure of.

A look at the formation of elements and the initial conditions of the universe

“We can now see the moment when the atomic nucleus and electrons merge in the afterglow. For the first time we see the creation of atoms, we can measure the temperature of matter, and we can see the microphysics of this distant explosion. It is like admiring three cosmic background radiations that surround us on all sides, but here we see everything from the side “We see before, during and after the birth of atoms,” says Rasmus Damgaard, a PhD student at the Cosmic DAWN Center and co-author of the study.

Co-author and assistant professor Casper Heinz of the Niels Bohr Institute continues: “Matter expands so quickly and increases in size so quickly that it takes hours for light to overcome the explosion. Therefore, by looking only at the far end of the fireball, we can better see the history of the explosion.” .

Electrons closer to us are clinging to the atomic nucleus, but on the other side, on the other side of the newborn black hole, the “present” is still only the future.