The temperature of elementary particles has been detected in the radioactive glow that follows the collision of two neutron stars and the formation of a black hole. This groundbreaking observation allows scientists to measure the tiny physical characteristics within these cosmic phenomena for the first time. Additionally, it demonstrates how momentary snapshots can portray objects that are unfolding over time.
The temperature of elementary particles has been detected in the radioactive glow produced by the collision of two neutron stars, which also lead to the formation of a black hole. This significant advance enables researchers to measure the microscopic, physical characteristics in these cosmic occurrences for the first time. It also highlights how instantaneous observations can reflect an object that is evolving over time. This discovery was made by astrophysicists from the Niels Bohr Institute, University of Copenhagen, and is detailed in the international scientific journal Astronomy & Astrophysics.
New observation technique reveals heavy elements’ creation
The collision of two neutron stars has resulted in the smallest black hole observed to date. This dramatic cosmic event not only led to the formation of a black hole but also created a fireball expanding at nearly the speed of light. In the following days, it radiated with a brightness similar to that of hundreds of millions of Suns.
This bright phenomenon, known as a kilonova, shines intensely due to the large amounts of radiation from the decay of heavy, radioactive elements formed during the explosion.
An international team of researchers, led by The Cosmic DAWN Center at the Niels Bohr Institute, has combined measurements taken from telescopes worldwide, working towards unraveling the mystery of this explosion and addressing a long-standing astrophysical question: What is the origin of elements heavier than iron?
Collaboration from observatories worldwide
“This astrophysical event evolves rapidly, so no single telescope can capture its entire progression since each telescope’s view of the event is hindered by Earth’s rotation.
However, by integrating existing measurements from locations in Australia, South Africa, and The Hubble Space Telescope, we can monitor its evolution in great detail.
Our findings illustrate that the complete picture reveals more than just the individual datasets,” says Albert Sneppen, a PhD student at the Niels Bohr Institute and lead author of the study.
The explosion mirrors the Universe shortly after the Big Bang
Immediately following the collision, the fractured star material reaches temperatures of several billion degrees—about a thousand times hotter than the core of the Sun and similar to the Universe’s temperature just one second post-Big Bang.
Such extreme heat causes electrons to drift freely, forming what is known as an ionized plasma, rather than being bound to atomic nuclei.
The electrons exhibit movement. However, as seconds, minutes, hours, and days pass, the star material cools down, akin to the cooling of the entire Universe after the Big Bang.
The signature of Strontium reveals the synthesis of heavy elements
About 370,000 years after the Big Bang, the Universe cooled to a point where electrons could attach to atomic nuclei, forming the very first atoms. At this stage, light was able to travel freely through the Universe, no longer hindered by free electrons.
This phenomenon produced the earliest light we can observe in the Universe’s history, referred to as “cosmic background radiation,” which forms a patchwork of light visible across the night sky. A similar unification of electrons and atomic nuclei can now be recognized in the star material resulting from the explosion.
One of the significant outcomes includes the detection of heavy elements like Strontium and Yttrium. While these elements are relatively easy to identify, it is probable that many other heavy elements of uncertain origin were also formed during the explosion.
“We can now observe the precise moment when atomic nuclei bond with electrons in the afterglow. For the first time, we witness the creation of atoms, allowing us to measure the matter’s temperature and examine the micro-physics of this distant explosion. It’s as if we are admiring three cosmic background radiations surrounding us, but here we observe everything externally, witnessing the phases before, during, and after atomic birth,” explains Rasmus Damgaard, a PhD student at the Cosmic DAWN Center and co-author of the study.
Kasper Heintz, co-author and assistant professor at the Niels Bohr Institute, adds: “The matter expands so rapidly that it takes several hours for light to traverse the explosion. Therefore, by simply viewing the farthest reaches of the fireball, we can look further back into the explosion’s history.
While the electrons nearby have combined with atomic nuclei, the “present” on the far side of the newly formed black hole remains merely future.
